GRIP Nutrient Management Ontology
type: Ontology
creator: GRIP, Kansas State University
license: Creative Commons Attribution 4.0 International
comment: The master ontology for the GRIP Nutrient Management suite developed at Kansas State University. This umbrella ontology imports five domain modules — environment, nutrient, fertilization, nitrogen cycle, and soil available nitrogen — and defines the shared root concept (Nutrient Management) that connects them into a coherent knowledge framework for describing, querying, and reasoning over nitrogen management experiments in crop production systems.

governed by
type: ObjectProperty
domain: Nutrient Management
range: Nitrogen Balance
comment: Links Nutrient Management to the Nitrogen Balance that governs the outcome. The balance between nitrogen supply and demand, mediated by transformations and losses, determines how much applied nitrogen reaches the crop versus being lost to the environment. Bridges to the nitrogen module.

has crop response
type: ObjectProperty
domain: Nutrient Management
range: Crop Response
comment: Links Nutrient Management to the Crop Response variables measured to evaluate the effectiveness of a management treatment. Responses include yield, growth, and quality measurements. Bridges to the nutrient module.

has environmental impact
type: ObjectProperty
domain: Nutrient Management
range: Environmental Impact
comment: Links Nutrient Management to the Environmental Impacts that may result from nitrogen losses. These are the externalities of nitrogen management — water pollution, soil acidification, atmospheric emissions — that the discipline seeks to minimise. Bridges to the soil available nitrogen module.

implemented through
type: ObjectProperty
domain: Nutrient Management
range: Nitrogen Fertilization
comment: Links Nutrient Management to the Nitrogen Fertilization decision and execution process that implements the management strategy. Encompasses source, rate, timing, and method choices. Bridges to the fertilization module.

involves cultivar
type: ObjectProperty
domain: Nutrient Management
range: Cultivar
comment: Links Nutrient Management to the Cultivar being grown. Cultivar genotype determines yield potential, nitrogen demand, and grain protein response. Bridges to the nutrient module.

involves nutrient
type: ObjectProperty
domain: Nutrient Management
range: Nutrient
comment: Links Nutrient Management to the Nutrient(s) it addresses. Every nutrient management programme targets at least one nutrient; nitrogen is the primary focus of this ontology suite but the structure supports extension to phosphorus, potassium, and micronutrients. Bridges to the nutrient module.

involves species
type: ObjectProperty
domain: Nutrient Management
range: Crop Species
comment: Links Nutrient Management to the Crop Species. Species determines fundamental nutrient requirements, growth habit, and the applicable set of response variables. Bridges to the nutrient module.

occurs in environment
type: ObjectProperty
domain: Nutrient Management
range: Environment
comment: Links Nutrient Management to the Environment in which it takes place. The environment (weather, soil, location, experimental design) constrains achievable yield, nitrogen dynamics, and loss risk. This property bridges the master ontology to the environment module.

has component
type: ObjectProperty
domain: Environment
range: Environment Component
comment: Relates an Environment to one of its constituent components (weather, soil, location, or experimental design). An Environment instance is expected to have multiple has_component assertions — at least one per component pillar.

has drainage class
type: ObjectProperty
domain: Soil Layer
range: Soil Drainage Class
comment: Associates a Soil Layer (or, by extension, the whole profile) with a USDA natural drainage class. Drainage class is typically assigned at the profile level, but attaching it at the layer level allows representing soils with contrasting drainage in different horizons (e.g., fragipan soils).

has nutrient status
type: ObjectProperty
domain: Soil Layer
range: Nutrient
comment: Associates a Soil Layer with a Nutrient (defined in the nutrient module) to record the availability or concentration of that nutrient at the given depth. Enables cross-module integration between environment and nutrient data.

has sampling depth
type: ObjectProperty
domain: Soil Layer
range: Sampling Depth
comment: Links a Soil Layer to the vertical interval (Sampling Depth) at which it was observed. Every Soil Layer must reference exactly one Sampling Depth to indicate where in the profile the associated traits and nutrient measurements were obtained.

has soil texture
type: ObjectProperty
domain: Soil Layer
range: Soil Texture
comment: Associates a Soil Layer with one of the 12 USDA soil textural classes. Texture is usually constant within a sampling interval but may change between layers (e.g., sandy loam surface over clay sub-soil).

has soil trait
type: ObjectProperty
domain: Soil Layer
range: Soil Trait
comment: Associates a Soil Layer with a measurable soil property (e.g., bulk density, pH, organic matter). A Soil Layer may have multiple trait assertions to capture the full suite of measurements taken at that depth.

is in state
type: ObjectProperty
domain: Geographic Entity
range: State
comment: Links a Geographic Entity (a County, a Weather Station, or any other state-anchored place) to its parent State. For Counties the link can be derived from the FIPS-5 code: its first two digits match the parent state's FIPS-2 code. For Weather Stations the link is recorded directly from the station metadata.

derived from factor
type: ObjectProperty
domain: Optimal Nitrogen Rate
range: Fertilization Decision Factor
comment: Indicates that an Optimal Nitrogen Rate was analytically derived using one or more Fertilization Decision Factors (yield goal, yield potential, protein response). The directionality is: the optimal rate is computed FROM these factors, not the reverse.

has adjustment
type: ObjectProperty
domain: Management Practice
range: Nitrogen Adjustment
comment: Links a Management Practice to the Nitrogen Adjustment (credit or debit in kg N/ha) it generates. The adjustment modifies the base nitrogen recommendation derived from decision factors.

has application
type: ObjectProperty
domain: Nitrogen Fertilization
range: Nitrogen Application
comment: Relates a Nitrogen Fertilization event to one or more discrete Nitrogen Application events that together implement the fertilization plan for a crop-season.

has crop category
type: ObjectProperty
domain: Previous Crop
range: Crop Category
comment: Links a Previous Crop to the broad agronomic category (cereals, legumes, oilseeds, fallow) that determines the direction and magnitude of the previous-crop nitrogen adjustment.

has depth
type: ObjectProperty
domain: Nitrogen Application
range: Application Depth
comment: Links a Nitrogen Application event to the Application Depth at which the fertilizer was placed. Applicable only for sub-surface methods (injection, deep banding); surface methods have no depth.

has method
type: ObjectProperty
domain: Nitrogen Application
range: Application Method
comment: Links a Nitrogen Application event to the Application Method (broadcast, injection, banding, etc.) used to place the fertilizer.

has rate
type: ObjectProperty
domain: Nitrogen Application
range: Nitrogen Rate
comment: Links a Nitrogen Application event to the Nitrogen Rate (quantity of elemental N per unit area) applied.

has source
type: ObjectProperty
domain: Nitrogen Application
range: Fertilizer Source
comment: Links a Nitrogen Application event to the Fertilizer Source (product) that was applied. A single application uses exactly one source; blended applications should be modeled as separate application events.

has timing
type: ObjectProperty
domain: Nitrogen Application
range: Application Timing
comment: Links a Nitrogen Application event to the Application Timing window (pre-plant, topdress, flag-leaf, etc.) at which it was executed.

influenced by cultivar
type: ObjectProperty
domain: Nitrogen Fertilization
range: Cultivar
comment: Relates a Nitrogen Fertilization decision to the Cultivar being grown. Cultivar determines genetic yield potential, nitrogen uptake efficiency, and grain protein response characteristics. Imported from the nutrient module.

influenced by environment
type: ObjectProperty
domain: Nitrogen Fertilization
range: Environment
comment: Relates a Nitrogen Fertilization decision to the Environment (weather, soil, location) that constrains achievable yield and nitrogen dynamics. Imported from the environment module.

influenced by factor
type: ObjectProperty
domain: Nitrogen Fertilization
range: Fertilization Decision Factor
comment: Relates a Nitrogen Fertilization decision to a Fertilization Decision Factor (yield goal, yield potential, protein response) that was used to determine the target nitrogen rate.

influenced by practice
type: ObjectProperty
domain: Nitrogen Fertilization
range: Management Practice
comment: Relates a Nitrogen Fertilization decision to a Management Practice (tillage, irrigation, grazing, manure, previous crop) that modifies the effective nitrogen requirement via adjustments.

associated with
type: ObjectProperty
domain: Fixing Organism Group
range: Nitrogen Fixation
comment: Links a nitrogen-fixing organism group to the fixation type (symbiotic or non-symbiotic) it participates in.

depleted by
type: ObjectProperty
domain: Soil Available Nitrogen
range: Nitrogen Loss
comment: Links Soil Available Nitrogen to the processes that remove nitrogen from the plant-available pool: crop uptake and the various loss pathways.

draws from
type: ObjectProperty
domain: Nitrogen Translocation
range: Nitrogen Pool
comment: Links Nitrogen Translocation to the nitrogen pools (mobilizable N in leaf, mobilizable N in stem) from which it remobilizes nitrogen for grain fill.

driven by
type: ObjectProperty
domain: Nitrogen Transformation
range: Soil Temperature
comment: Links a nitrogen process (mineralization, nitrification, denitrification) to the environmental variable that regulates its rate. This replaces the former subClassOf relationship between drivers and processes.

fulfilled by
type: ObjectProperty
domain: Grain Nitrogen Demand
range: Nitrogen Translocation
comment: Links Grain Nitrogen Demand to the Nitrogen Translocation process that supplies the majority of grain nitrogen by remobilizing pre-anthesis vegetative nitrogen.

has computation
type: ObjectProperty
domain: Organ Nitrogen Demand
range: Nitrogen Demand Computation
comment: Links an organ-level nitrogen demand to the mathematical computation procedure that calculates its magnitude from physiological input parameters.

has demand
type: ObjectProperty
domain: Nitrogen Balance
range: Nitrogen Demand
comment: Links Nitrogen Balance to its demand side — the aggregate of all nitrogen required by the crop.

has determinant
type: ObjectProperty
domain: Nitrogen Demand
range: Crop Growth Stage
comment: Links Nitrogen Demand to a variable that is a necessary computational input for calculating the demand quantity. Determinants directly enter the demand equation: growth stage, critical N requirement, and uptake capacity.

has loss
type: ObjectProperty
domain: Nitrogen Balance
range: Nitrogen Loss
comment: Links Nitrogen Balance to the loss pathways that permanently remove nitrogen from the soil-plant system.

has parameter
type: ObjectProperty
domain: Nitrogen Demand Computation
range: Computation Parameter
comment: Links a Nitrogen Demand Computation to one of its input variables (a Computation Parameter). Parameters are measurable physiological values that enter the computation equation; they are not types of the computation itself.

has substrate
type: ObjectProperty
domain: Mineralization
range: Mineralization Substrate
comment: Links Mineralization to the organic material from which nitrogen is being released through microbial decomposition.

has supply
type: ObjectProperty
domain: Nitrogen Balance
range: Nitrogen Supply
comment: Links Nitrogen Balance to its supply side — the aggregate of all nitrogen inputs entering the system.

has transformation
type: ObjectProperty
domain: Nitrogen Balance
range: Nitrogen Transformation
comment: Links Nitrogen Balance to transformations that change nitrogen form without altering the total pool size.

is parameter of
type: ObjectProperty
domain: Computation Parameter
range: Nitrogen Demand Computation
comment: Inverse of has_parameter. Links a Computation Parameter to the Nitrogen Demand Computation in which it is used as an input variable.

modulated by
type: ObjectProperty
domain: Nitrogen Demand
range: Growing Season
comment: Links Nitrogen Demand to an external factor that modifies the rate or magnitude of demand without being a direct computational input. Modulators alter the context in which demand operates: growing season length, pest pressure, other nutrient limitations.

supplied through
type: ObjectProperty
domain: Soil Available Nitrogen
range: Nitrogen Supply Source
comment: Links Soil Available Nitrogen to the supply sources that contribute nitrogen to the plant-available pool.

has crop response
type: ObjectProperty
domain: Nutrient Management
range: Crop Response
comment: Links Nutrient Management to the set of crop response variables measured to evaluate treatment effects.

has measure
type: ObjectProperty
domain: Crop Response
range: Crop Response
comment: Links a Crop Response category (Yield_Response, Growth_Response, Quality_Response) to the specific measurement variables it contains. Retained for backward compatibility where needed but the preferred pattern is direct individual → class typing.

has species
type: ObjectProperty
domain: Cultivar
range: Crop Species
comment: Links a Cultivar to the Crop Species it belongs to. Every cultivar belongs to exactly one species; the species determines the set of applicable response variables (e.g., wheat-specific milling quality measures).

involves nutrient
type: ObjectProperty
domain: Nutrient Management
range: Nutrient
comment: Links Nutrient Management to the nutrients it addresses. Every nutrient management programme targets at least one nutrient.

is form of
type: ObjectProperty
domain: Nutrient Form
range: Nutrient
comment: Links a Nutrient Form (e.g., Ammonium_Nitrogen, Nitrate_Nitrogen) to the parent Nutrient element it represents. A given element may have multiple forms with different soil mobility and availability characteristics.

observed in response to
type: ObjectProperty
domain: Crop Response
range: Nutrient
comment: Links a Crop Response observation to the Nutrient(s) whose management treatment it evaluates. This replaces the previous vague 'Nutrient influence Observational_Traits' assertion with a precise, queryable relationship. Example: a Grain_Protein measurement observed_in_response_to Nitrogen.

has location
type: ObjectProperty
domain: Site-Year Environment
range: Location
comment: Links a Site-Year Environment to its Location.

has maturity group
type: ObjectProperty
domain: Cultivar
range: Maturity Group
comment: Links a Cultivar to its Maturity Group classification.

has treatment 1
type: ObjectProperty
domain: Plot Observation
range: Treatment Factor
comment: Links a Plot Observation to its primary treatment factor (Treatment 1). This is either a 'Fertility' treatment (varying nitrogen rates or management packages like FP, FP+N+MESZ) or a 'Management' treatment (overall management intensity like High, High_N).

has treatment 2
type: ObjectProperty
domain: Plot Observation
range: Treatment Factor
comment: Links a Plot Observation to its secondary treatment factor (Treatment 2). This is always 'Variety' — the cultivar being tested. The specific cultivar identity is also available via the observed_cultivar property for direct access without going through the Treatment_Factor indirection.

has treatment 3
type: ObjectProperty
domain: Plot Observation
range: Treatment Factor
comment: Links a Plot Observation to its tertiary treatment factor (Treatment 3), if present. This is either an 'N timing' treatment (fall/spring/anthesis split) or a 'Plant Growth Regulator' treatment (Control vs Palisade). Not all trials have a third factor.

has year
type: ObjectProperty
domain: Site-Year Environment
range: Year
comment: Links a Site-Year Environment to its crop-season Year.

observed at site-year
type: ObjectProperty
domain: Plot Observation
range: Site-Year Environment
comment: Links a Plot Observation to the Site-Year Environment in which it was recorded.

observed cultivar
type: ObjectProperty
domain: Plot Observation
range: Cultivar
comment: Links a Plot Observation to the Cultivar grown in the plot.

observed in trial
type: ObjectProperty
domain: Plot Observation
range: Trial
comment: Links a Plot Observation to the Trial it belongs to.

observed N timing
type: ObjectProperty
domain: Plot Observation
range: Nitrogen Timing Split
comment: Links a Plot Observation to the Nitrogen Timing Split used for the nitrogen application in that plot.

observed previous crop
type: ObjectProperty
domain: Plot Observation
range: Previous Crop
comment: Links a Plot Observation to the actual Previous Crop grown in the field in the preceding season (e.g., Soybeans, Wheat, Canola, Fallow). The previous crop individual is in turn linked to its broad Crop Category (Legumes, Cereals, etc.) via has_crop_category.

causes impact
type: ObjectProperty
domain: Nitrogen Loss
range: Environmental Impact
comment: Links a nitrogen loss pathway or transformation process to the environmental impact it produces. Each loss pathway may cause one or more distinct impacts: leaching causes water pollution, denitrification causes atmospheric pollution, nitrification causes soil acidification. Directionality is causal: the process produces the impact as an externality.

contributes to
type: ObjectProperty
domain: Nitrogen Uptake
range: Crop Response
comment: Links nitrogen uptake to the crop response variable it positively influences. Uptake contributes to yield (more N absorbed → more biomass and grain) and quality (more N absorbed → higher grain protein). The relationship is directional and causal but not exclusive — other factors (genetics, weather, disease) also determine yield and quality.

has determinant
type: ObjectProperty
domain: Nitrogen Uptake
range: Root Growth
comment: Links nitrogen uptake to a factor that is a necessary determinant of uptake capacity. Root growth is the primary determinant because it defines the volume of soil accessible to the plant for nitrogen absorption.

mediated by
type: ObjectProperty
domain: Denitrification
range: Denitrifying Organism
comment: Links a biogeochemical process (denitrification) to the microbial organism group that catalyses it. Indicates that the process cannot occur abiotically and requires biological mediation.

quantified by
type: ObjectProperty
domain: Soil Available Nitrogen
range: Soil Mineral Nitrogen Content
comment: Links the conceptual Soil Available Nitrogen pool (defined in the nitrogen module) to the measurable Soil Mineral Nitrogen Content that quantifies it through laboratory analysis. The pool is the abstract compartment; the measurement is its empirical expression.

has FIPS code
type: DatatypeProperty
domain: Geographic Region
range: string
comment: The Federal Information Processing Standards (FIPS) code that uniquely identifies a Geographic Region. State FIPS codes are two digits with a leading zero where applicable (e.g., '05' for Arkansas, '20' for Kansas). County FIPS codes are five digits where the first two digits match the parent state (e.g., '20015' for Allen County, Kansas). Stored as xsd:string to preserve leading zeros.

has lower depth (cm)
type: DatatypeProperty
domain: Sampling Depth
range: float
comment: The lower (deeper) boundary of a sampling depth interval, measured in centimeters from the soil surface. The thickness of the interval is (has_lower_depth_cm − has_upper_depth_cm).

has station ID
type: DatatypeProperty
domain: Weather Station
range: string
comment: The station identifier as assigned by the operating network (NWS Cooperative Observer Program, ASOS, AWOS, or a state mesonet). Examples: 'RSL 3' for Russell Municipal Airport, Kansas. Stored as xsd:string because IDs may contain spaces, letters, and digits with no fixed length.

has upper depth (cm)
type: DatatypeProperty
domain: Sampling Depth
range: float
comment: The upper (shallower) boundary of a sampling depth interval, measured in centimeters from the soil surface. A value of 0.0 indicates the surface.

has K₂O percent
type: DatatypeProperty
domain: Fertilizer Source
range: float
comment: The guaranteed potassium content of a fertilizer source, expressed as weight-percent K₂O (industry convention). Zero for most nitrogen and phosphorus sources.

has N percent
type: DatatypeProperty
domain: Fertilizer Source
range: float
comment: The guaranteed nitrogen content of a fertilizer source, expressed as weight-percent elemental N. For example, urea = 46.0, DAP = 18.0. Enables nitrogen-budget queries: SELECT all sources WHERE has_N_percent > 0.

has P₂O₅ percent
type: DatatypeProperty
domain: Fertilizer Source
range: float
comment: The guaranteed phosphorus content of a fertilizer source, expressed as weight-percent P₂O₅ (industry convention). For example, DAP = 46.0, MAP = 52.0. Zero for nitrogen-only sources.

has S percent
type: DatatypeProperty
domain: Fertilizer Source
range: float
comment: The guaranteed sulfur content of a fertilizer source, expressed as weight-percent elemental S. For example, ammonium sulfate = 24.0. Zero for sources without sulfur.

has depth (cm)
type: DatatypeProperty
domain: Application Depth
range: float
comment: The numeric depth of fertilizer placement below the soil surface, in centimeters. Applicable only for sub-surface application methods (injection, deep banding).

has rate value
type: DatatypeProperty
domain: Nitrogen Rate
range: float
comment: The numeric value of the nitrogen rate in kg N/ha (or lb N/acre when specified by unit context). Associates a Nitrogen Rate instance with its scalar magnitude.

has anthesis percent
type: DatatypeProperty
domain: Nitrogen Timing Split
range: integer
comment: The percentage of total nitrogen applied at anthesis (0-100).

has biomass (g/m2)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: Total aboveground biomass at maturity, in grams per square meter.

has DAP N contribution (lbs/acre)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The nitrogen contributed by DAP application, in lbs N per acre. Calculated from DAP rate and its 18% N content.

has DAP rate (lbs/acre)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The di-ammonium phosphate application rate in lbs product per acre at sowing.

has estimated anthesis date
type: DatatypeProperty
domain: Plot Observation
range: date
comment: The estimated date of anthesis (flowering) for the plot.

has factor level
type: DatatypeProperty
domain: Treatment Factor
range: string
comment: The specific level or treatment description within the factor (e.g., 'N rate', 'FP', 'FP+N+MESZ', 'MESZ', 'High', 'High_N', '40/60/0', 'Palisade').

has factor name
type: DatatypeProperty
domain: Treatment Factor
range: string
comment: The name of the treatment factor (e.g., 'Fertility', 'Management', 'Variety', 'N timing').

has fall percent
type: DatatypeProperty
domain: Nitrogen Timing Split
range: integer
comment: The percentage of total nitrogen applied in fall (0-100).

has fungicide date
type: DatatypeProperty
domain: Plot Observation
range: date
comment: The date on which foliar fungicide was applied.

has harvest index
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The ratio of grain yield to total aboveground biomass (dimensionless, 0-1).

has heads per m2
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The count of fertile spikes (heads) per square meter.

has kernels per head
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The average number of grains per spike.

has kernels per m2
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The total number of grains per square meter.

has N rate (lbs/acre)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The nitrogen fertilizer rate applied, in lbs N per acre.

has plot number
type: DatatypeProperty
domain: Plot Observation
range: integer
comment: The numeric plot identifier within the trial.

has protein (% dry basis)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: Whole-grain protein concentration on a dry-weight basis.

has rep number
type: DatatypeProperty
domain: Plot Observation
range: integer
comment: The replication (block) number.

has seed rate (lbs/acre)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The seeding rate in pounds per acre.

has soil NO3-N (lbs/acre, 0-60cm)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: Pre-plant soil nitrate-nitrogen in the 0-60 cm profile, in lbs N per acre. Measured by KCl extraction.

has sowing date
type: DatatypeProperty
domain: Plot Observation
range: date
comment: The date on which the plot was planted/sown.

has spring percent
type: DatatypeProperty
domain: Nitrogen Timing Split
range: integer
comment: The percentage of total nitrogen applied in spring (0-100).

has test weight (lbs/bu)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: Grain test weight in pounds per bushel.

has thousand kernel weight (g)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The mass of 1000 individual grains, in grams.

has total N (lbs/acre)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: The total nitrogen available to the crop: the sum of applied fertilizer N, DAP N contribution, and pre-plant soil NO3-N.

has yield (lbs/acre, 13% moisture)
type: DatatypeProperty
domain: Plot Observation
range: float
comment: Grain yield adjusted to 13% moisture, in lbs per acre.

Nutrient Management
type: Class
subclass of: Restriction
  on property: governed by
  some values from: Nitrogen Balance
subclass of: Restriction
  on property: has crop response
  some values from: Crop Response
subclass of: Restriction
  on property: has environmental impact
  some values from: Environmental Impact
subclass of: Restriction
  on property: implemented through
  some values from: Nitrogen Fertilization
subclass of: Restriction
  on property: involves cultivar
  some values from: Cultivar
subclass of: Restriction
  on property: involves nutrient
  some values from: Nutrient
subclass of: Restriction
  on property: involves species
  some values from: Crop Species
subclass of: Restriction
  on property: occurs in environment
  some values from: Environment
subclass of: Restriction
  on property: has crop response
  some values from: Crop Response
subclass of: Restriction
  on property: involves nutrient
  some values from: Nutrient
comment: The overarching discipline of optimising the supply of plant nutrients to achieve agronomic, economic, and environmental objectives. This root concept connects all five modules of the ontology suite: it operates within an Environment, targets one or more Nutrients, is implemented through Nitrogen Fertilization decisions, is governed by the Nitrogen Balance between supply and demand, produces measurable Crop Responses, and may generate Environmental Impacts as externalities. Nutrient Management is the entry point from which any cross-module query can begin.

Aspect
type: Class
subclass of: Location Component
comment: The compass direction (azimuth) that a hillslope faces, expressed in degrees from north (0–360°). Aspect influences the amount and timing of incoming solar radiation, affecting soil temperature, evaporation rate, snowmelt timing, and microclimate — all of which modify nutrient cycling dynamics.

Bulk Density
type: Class
subclass of: Soil Trait
comment: The mass of oven-dry soil per unit bulk volume (g/cm³ or Mg/m³), including pore space. Indicates compaction status; affects root penetration, water infiltration, and aeration — all of which influence nutrient accessibility and microbial activity.

Cation Exchange Capacity
type: Class
subclass of: Soil Trait
comment: The total quantity of exchangeable cations that the soil can adsorb, expressed in centimoles of charge per kilogram (cmolc/kg) or milliequivalents per 100 g (meq/100 g). Governs the soil's ability to retain positively charged nutrients (K⁺, Ca²⁺, Mg²⁺, NH₄⁺) against leaching.

County
type: Class
subclass of: Geographic Region
subclass of: Restriction
  on property: is in state
  some values from: State
comment: A second-level administrative subdivision of the United States, identified by a five-digit FIPS code where the first two digits match the parent state (e.g., 20015 for Allen County, Kansas). Counties are the finest standard geographic unit at which the US Drought Monitor and most agricultural statistics are reported. Every County instance is linked to its parent State via the is_in_state property.

Dew Point Temperature
type: Class
subclass of: Temperature
comment: The temperature to which air must be cooled at constant pressure for water vapor to begin condensing. Indicates absolute moisture content and is used to calculate vapor pressure deficit.

Electrical Conductivity
type: Class
subclass of: Soil Trait
comment: A measure of the soil solution's ability to conduct an electrical current (dS/m or mS/cm). Serves as a proxy for soluble salt concentration; elevated values indicate salinity stress that can impair nutrient uptake and crop growth.

Elevation
type: Class
subclass of: Location Component
comment: The height of the experimental site above mean sea level, typically reported in meters (m). Elevation influences temperature lapse rate, atmospheric pressure, precipitation patterns, and the length of the frost-free growing season.

Environment
type: Class
subclass of: Restriction
  on property: has component
  some values from: Environment Component
comment: The complete environmental context surrounding a nutrient-management experiment. An Environment is composed of one or more Environment Components that together describe the weather, soil, geographic location, and experimental design under which field observations were collected.

Environment Component
type: Class
comment: Abstract superclass for any first-order component that characterises the experimental environment. Concrete subclasses include Weather Component, Soil Component, Location Component, and Experimental Component.

Evapotranspiration
type: Class
subclass of: Weather Component
comment: Combined water loss from soil evaporation and plant transpiration, reported in mm/day or mm/period. May be reference ET₀ (grass or alfalfa reference) or crop-specific ETc. The dominant pathway of water removal from the root zone and a critical factor in nutrient leaching risk assessment and irrigation scheduling.

Experimental Component
type: Class
subclass of: Environment Component
comment: Descriptors of the experimental design and structure: the site or location identity, individual plots, replications, trials, and the year(s) of observation.

Geographic Entity
type: Class
subclass of: Location Component
comment: An umbrella class for named places that observations or other data can attach to. Distinct from the point-level Location Component descriptors (latitude, longitude, elevation), which describe spatial properties OF a place. Geographic Entity covers both areas (Geographic Region: State, County) and points (Weather Station). Anything that can answer 'which state is this in?' is a Geographic Entity.

Geographic Region
type: Class
subclass of: Geographic Entity
comment: An area-level Geographic Entity bounded by an administrative or natural boundary, such as a state, county, watershed, or climate division. Concrete subclasses include State and County. Geographic Regions carry FIPS codes and are the unit at which USDA, NOAA, and US Drought Monitor data are aggregated.

Growing Degree Days
type: Class
subclass of: Weather Component
comment: Accumulated thermal units calculated as the daily sum of (T_mean − T_base) for days where T_mean exceeds T_base. Units are °C·day or °F·day. Used extensively to predict crop phenological stage and to time split nitrogen applications relative to growth stage rather than calendar date.

Hydraulic Conductivity
type: Class
subclass of: Soil Trait
comment: The rate at which water moves through the soil matrix under a unit hydraulic gradient (cm/hr or mm/day). Determines how quickly water and dissolved nutrients (especially nitrate) percolate through the profile, directly affecting leaching risk.

Latitude
type: Class
subclass of: Location Component
comment: The angular distance of the experimental site north or south of the equator, expressed in decimal degrees (WGS 84). Together with longitude, provides the fundamental geospatial reference for linking field data to climate grids, soil surveys, and remote-sensing products.

Location
type: Class
subclass of: Experimental Component
comment: The named site or field station at which an experiment is conducted. Distinct from the geospatial Location Component; this is the experimental identity label (e.g., 'Ashland Bottoms', 'Tribune') used to group trials.

Location Component
type: Class
subclass of: Environment Component
comment: Geospatial descriptors that fix the experimental site on the Earth's surface. Includes geographic coordinates, elevation, slope gradient, and slope aspect — all of which influence microclimate, runoff patterns, and nutrient transport.

Longitude
type: Class
subclass of: Location Component
comment: The angular distance of the experimental site east or west of the Prime Meridian, expressed in decimal degrees (WGS 84). Required alongside latitude for unambiguous georeferencing.

Maximum Temperature
type: Class
subclass of: Temperature
comment: The highest air temperature recorded during a defined observation period (usually 24 hours). Drives daytime evapotranspiration and heat-stress thresholds for crops.

Maximum Vapor Pressure Deficit
type: Class
subclass of: Vapor Pressure Deficit
comment: The highest VPD value recorded during the observation period. Typically coincides with peak afternoon temperature and lowest relative humidity; indicates the maximum atmospheric water demand experienced by the crop canopy.

Mean Temperature
type: Class
subclass of: Temperature
comment: The arithmetic average of air temperature over a defined observation period. Used as the basis for growing degree day (GDD) calculations and general thermal characterisation of the growing season.

Minimum Temperature
type: Class
subclass of: Temperature
comment: The lowest air temperature recorded during a defined observation period (usually 24 hours). Governs frost risk and overnight respiration rates in crops.

Minimum Vapor Pressure Deficit
type: Class
subclass of: Vapor Pressure Deficit
comment: The lowest VPD value recorded during the observation period. Typically occurs near dawn when temperature is lowest and humidity is highest; relevant to dew formation and foliar disease pressure.

Particle Density
type: Class
subclass of: Soil Trait
comment: The mass per unit volume of solid soil particles only, excluding pore space (typically ≈2.65 g/cm³ for mineral soils). Used together with bulk density to calculate total porosity, which governs water and air storage capacity.

Plot
type: Class
subclass of: Experimental Component
comment: The smallest spatial unit within an experimental design to which a single treatment is applied. Plot identity is essential for linking measured soil traits, yield observations, and treatment details to the correct spatial replicate.

Precipitation
type: Class
subclass of: Weather Component
comment: Water input reaching the soil surface from atmospheric sources, measured in millimeters (mm). Includes rainfall, snowmelt, and sleet. A primary control on soil moisture recharge, nutrient leaching, and surface runoff of dissolved and particulate nutrients.

Relative Humidity
type: Class
subclass of: Weather Component
comment: The ratio of the actual water vapor pressure to the saturation water vapor pressure at the same temperature, expressed as a percentage (%). Influences evapotranspiration rate, foliar nutrient uptake efficiency, and disease incidence.

Replication
type: Class
subclass of: Experimental Component
comment: A complete set of treatments within a block of the experimental design. Replication identity tracks which repetition of a treatment an observation belongs to, enabling proper statistical analysis (e.g., RCBD, split-plot ANOVA).

Sampling Depth
type: Class
subclass of: Soil Component
comment: A defined vertical interval in the soil profile, bounded by an upper and lower depth (in centimeters from the surface). Sampling depths are referenced by Soil Layer instances to indicate where in the profile a measurement was taken. Common intervals are pre-defined as named individuals; additional depths can be freely instantiated.

Slope
type: Class
subclass of: Location Component
comment: The inclination of the land surface at the experimental site, expressed in degrees or as a percentage (rise/run × 100). Slope gradient controls the velocity and volume of surface runoff, which in turn governs soil erosion rates and the off-site transport of dissolved and particulate nutrients.

Soil Component
type: Class
subclass of: Environment Component
comment: Any aspect of the soil system relevant to nutrient availability, transformation, and transport. Encompasses physical, chemical, and biological soil properties, textural classification, drainage, and the vertical stratification of the soil profile.

Soil Drainage Class
type: Class
subclass of: Soil Trait
comment: The USDA natural soil drainage classification, describing the frequency and duration of wet periods under conditions similar to those under which the soil formed. Drainage class directly influences water-table depth, oxygen availability in the root zone, denitrification losses, and the risk of nutrient leaching versus waterlogging.

Soil Layer
type: Class
subclass of: Soil Component
subclass of: Restriction
  on property: has nutrient status
  some values from: Nutrient
subclass of: Restriction
  on property: has sampling depth
  some values from: Sampling Depth
subclass of: Restriction
  on property: has soil trait
  some values from: Soil Trait
comment: A conceptual entity representing the soil at a particular sampling depth. This is the class to which soil traits, nutrient status, textural classification, and drainage class attach. Separating the layer from the depth interval avoids the semantic error of ascribing measurable properties to a dimensionless interval rather than to the material within it.

Soil Moisture
type: Class
subclass of: Soil Trait
comment: The volumetric or gravimetric water content of the soil at the time of measurement. Controls nutrient diffusion to root surfaces, microbial mineralization rates, and the redox status that governs denitrification.

Soil Organic Matter
type: Class
subclass of: Soil Trait
comment: The fraction of the soil composed of plant and animal residues at various stages of decomposition, usually expressed as a percentage by weight. The principal reservoir of organically bound nitrogen, phosphorus, and sulfur; a key determinant of CEC, water-holding capacity, and soil biological activity.

Soil Temperature
type: Class
subclass of: Soil Trait
comment: Temperature measured within the soil profile at a specified depth, reported in °C or °F. Regulates the rate of microbial mineralization and nitrification, seed germination, root elongation, and the volatilization of surface-applied urea. Although correlated with air temperature, it lags and is buffered by soil thermal properties.

Soil Texture
type: Class
subclass of: Soil Trait
comment: The USDA soil textural class, determined by the relative mass proportions of sand (0.05–2.0 mm), silt (0.002–0.05 mm), and clay (<0.002 mm) particles. Texture governs water-holding capacity, permeability, workability, and nutrient retention. The 12 standard USDA classes are modeled as named individuals because they form a closed enumeration — not types that can be further specialized.

Soil Trait
type: Class
subclass of: Soil Component
comment: A measurable physical, chemical, or biological property of the soil. Soil traits are observed within a specific Soil Layer (i.e. at a given sampling depth) and collectively determine the soil's capacity to supply, retain, and transport nutrients.

Soil pH
type: Class
subclass of: Soil Trait
comment: The negative logarithm of the hydrogen-ion activity in the soil solution (dimensionless, scale 0–14). Controls the solubility and plant availability of nearly every essential nutrient; strongly influences aluminum toxicity risk and microbial community composition.

Solar Radiation
type: Class
subclass of: Weather Component
comment: Total incoming shortwave radiation at the Earth's surface, typically reported as a daily integral in MJ/m²/day. Drives photosynthesis (via photosynthetically active radiation, PAR), is a key input to Penman-Monteith reference ET estimation, and influences soil temperature dynamics.

State
type: Class
subclass of: Geographic Region
comment: A first-level administrative subdivision of the United States, identified by a two-digit FIPS code (e.g., 20 for Kansas) and a standard name. States are the coarsest geographic unit at which USDA, NOAA, and US Drought Monitor data are reported. Used to anchor regional observations such as weekly drought severity, climate summaries, and county aggregations.

Temperature
type: Class
subclass of: Weather Component
comment: Air temperature measured at standard meteorological height (typically 2 m above ground level). Serves as the parent class for specific aggregation types (maximum, minimum, mean) and dew point.

Trial
type: Class
subclass of: Experimental Component
comment: A discrete experiment or study conducted at one location in one or more years. A trial defines the research question, treatment structure, and design that connect environment, management, and response data.

Vapor Pressure Deficit
type: Class
subclass of: Weather Component
comment: The difference between the saturation vapor pressure and the actual vapor pressure of the air, expressed in kilopascals (kPa). VPD is derived from BOTH temperature and relative humidity and is therefore not a temperature measure. It quantifies the atmospheric drying power and is a primary driver of transpiration and stomatal conductance in crops.

Weather Component
type: Class
subclass of: Environment Component
comment: Atmospheric and climatic variables measured at or near the experimental site. Includes temperature, precipitation, humidity, wind, radiation, evapotranspiration, and derived thermal indices.

Weather Station
type: Class
subclass of: Geographic Entity
subclass of: Restriction
  on property: is in state
  some values from: State
subclass of: Restriction
  on property: has station ID
  some values from: string
comment: A fixed, point-located observation station that reports weather measurements (typically daily): maximum and minimum air temperature, precipitation, snowfall, snow depth, and similar variables. Each station is identified by a station ID assigned by its operator (NWS COOP, ASOS, AWOS, or a state mesonet) and is geographically anchored to a parent State via is_in_state. Future revisions may add latitude, longitude, and elevation as Location Component descriptors on individual stations.

Wind Speed
type: Class
subclass of: Weather Component
comment: Horizontal wind velocity measured at standard anemometer height (typically 2 m or 10 m), expressed in m/s or km/h. Affects boundary-layer resistance to evapotranspiration, physical crop damage, and the drift distance of aerially applied fertilizers or pesticides.

Year
type: Class
subclass of: Experimental Component
comment: The calendar or crop-season year in which observations were recorded. Year serves as a temporal key for multi-year trials and captures inter-annual environmental variability.

Agronomic Optimal Nitrogen Rate
type: Class
subclass of: Optimal Nitrogen Rate
comment: The nitrogen rate at which grain yield (or total biomass) is maximised, estimated from the plateau or maximum of a fitted yield–nitrogen response function (quadratic, quadratic-plateau, or linear-plateau). Does not consider input costs or grain price.

Application Depth
type: Class
comment: The vertical depth below the soil surface at which fertilizer material is placed during sub-surface application methods such as injection or deep banding. Depth affects nitrogen retention, volatilisation risk, and root access. Expressed in centimeters.

Application Method
type: Class
comment: The physical technique used to deliver a fertilizer to or into the soil. The choice of method affects placement uniformity, volatilisation risk, root proximity, and labour/equipment requirements.

Application Timing
type: Class
comment: The temporal window within the cropping cycle at which a nitrogen application event occurs. Timing relative to crop growth stage is the single most important management lever for nitrogen use efficiency: matching supply to demand minimises loss pathways (leaching, denitrification, volatilisation).

Crop Category
type: Class
comment: A broad agronomic grouping of crops used to classify the previous crop for nitrogen credit determination. The primary distinction is between nitrogen-fixing legumes (which leave a nitrogen credit) and non-fixing cereals/grasses (which may immobilise nitrogen during residue decomposition).

Economic Optimal Nitrogen Rate
type: Class
subclass of: Optimal Nitrogen Rate
comment: The nitrogen rate at which marginal return (value of additional yield) equals marginal cost (price of additional nitrogen), i.e. the rate that maximises net profit. Always ≤ the agronomic optimum because the yield response function has diminishing returns near its maximum.

Enhanced Efficiency Fertilizer
type: Class
subclass of: Synthetic Fertilizer
comment: A fertilizer product engineered to improve nutrient availability timing and reduce losses. Includes products with nitrification inhibitors, urease inhibitors, or controlled-release coatings. Categorised as a subclass of Synthetic_Fertilizer because the base product is always a synthetic N source with an added modifier.

Fertilization Decision Factor
type: Class
comment: An agronomic or economic variable that informs the choice of how much nitrogen to apply. Decision factors are inputs to recommendation algorithms and are conceptually distinct from management practices (which modify the nitrogen requirement after the base target has been set).

Fertilizer Source
type: Class
comment: A commercial or on-farm material applied to supply one or more plant nutrients. Each source is described by its guaranteed analysis — the weight-percent of N, P₂O₅, K₂O, and S it contains. This generalisation avoids pigeon-holing multi-nutrient products (e.g., DAP 18-46-0) into a single nutrient category while still enabling nitrogen-budget queries by filtering on has_N_percent > 0.

Grain Protein Response
type: Class
subclass of: Fertilization Decision Factor
comment: The empirical relationship between nitrogen rate and grain protein concentration. In hard wheat production regions, protein premiums or discounts at the elevator make this relationship a key decision factor: additional nitrogen beyond the yield plateau may still be profitable if it raises protein into a premium bracket.

Grazing
type: Class
subclass of: Management Practice
subclass of: Restriction
  on property: has adjustment
  some values from: Grazing Adjustment
comment: The use of livestock to harvest forage from a dual-purpose or graze-out crop. Grazing removes biomass and the nitrogen it contains, but returns a portion via excreta (urine and dung). The net effect on nitrogen requirement depends on stocking rate, grazing duration, and the proportion of nitrogen recycled.

Grazing Adjustment
type: Class
subclass of: Nitrogen Adjustment
comment: The nitrogen adjustment for dual-purpose crops that have been grazed. Grazing removes nitrogen in animal product (body gain, milk) but recycles a large fraction via excreta. The net adjustment depends on stocking density and grazing duration; K-State guidelines provide specific debit values for grazed wheat.

Irrigation
type: Class
subclass of: Management Practice
comment: The artificial application of water to supplement precipitation. Irrigated systems generally support higher yield goals and thus higher nitrogen rates, but also increase leaching risk if nitrogen is applied in excess of crop uptake capacity.

Management Practice
type: Class
comment: An agronomic action or field condition (other than fertilization itself) that modifies the effective nitrogen requirement. Management practices generate nitrogen adjustments (credits or debits) that are applied to the base recommendation derived from decision factors.

Manure Application
type: Class
subclass of: Management Practice
comment: The field application of animal manure as a nutrient source. Manure supplies nitrogen (and other nutrients) with variable availability that depends on manure type, application method, timing, and environmental conditions. The first-year plant-available N must be credited against the mineral fertilizer recommendation.

Nitrogen Adjustment
type: Class
comment: A quantitative credit (reduction) or debit (increase) applied to the base nitrogen recommendation to account for a specific management practice. Adjustments are expressed in kg N/ha or lb N/acre. For example, a soybean previous-crop credit might reduce the recommendation by 40 kg N/ha.

Nitrogen Application
type: Class
subclass of: Restriction
  on property: has method
  some values from: Application Method
subclass of: Restriction
  on property: has rate
  some values from: Nitrogen Rate
subclass of: Restriction
  on property: has source
  some values from: Fertilizer Source
subclass of: Restriction
  on property: has timing
  some values from: Application Timing
comment: A discrete event in which a nitrogen-containing material is applied to a field. Each application event is characterised by its source (fertilizer product), rate (kg N/ha), timing (growth stage or calendar window), method (how the material is placed), and — for sub-surface methods — application depth.

Nitrogen Fertilization
type: Class
subclass of: Nitrogen Supply Source
subclass of: Restriction
  on property: has application
  some values from: Nitrogen Application
subclass of: Restriction
  on property: influenced by cultivar
  some values from: Cultivar
subclass of: Restriction
  on property: influenced by environment
  some values from: Environment
subclass of: Restriction
  on property: influenced by factor
  some values from: Fertilization Decision Factor
subclass of: Restriction
  on property: influenced by practice
  some values from: Management Practice
comment: The overarching concept representing the complete nitrogen fertilization decision and execution for a crop. Encompasses the choice of rate, source, timing, and method of application as well as the environmental and agronomic factors that inform the decision. Serves as the root node of the fertilization module hierarchy.

Nitrogen Rate
type: Class
comment: The quantity of elemental nitrogen applied per unit area in a single application event, expressed in kg N/ha or lb N/acre. The applied rate may equal, exceed, or fall short of the agronomically or economically optimal rate, depending on the recommendation system used and operational constraints.

Optimal Nitrogen Rate
type: Class
subclass of: Nitrogen Rate
subclass of: Restriction
  on property: derived from factor
  some values from: Fertilization Decision Factor
comment: An analytically derived nitrogen rate that maximises a defined objective function. Optimal rates are estimated from multi-rate response trials, crop models, or sensor-based algorithms; they are not the rate actually applied but the rate that retrospective or predictive analysis identifies as best.

Organic Nutrient Source
type: Class
subclass of: Fertilizer Source
comment: A nutrient source derived from biological materials: animal manures, composts, biosolids, or green manures. Organic sources release nitrogen through mineralisation and their N availability depends on the C:N ratio, application timing, and environmental conditions.

Previous Crop
type: Class
subclass of: Management Practice
subclass of: Restriction
  on property: has adjustment
  some values from: Previous Crop Adjustment
subclass of: Restriction
  on property: has crop category
  some values from: Crop Category
comment: The crop grown in the field in the season immediately preceding the current crop. The previous crop influences residual soil nitrogen through residue decomposition and, in the case of legumes, biological nitrogen fixation credits.

Previous Crop Adjustment
type: Class
subclass of: Nitrogen Adjustment
comment: The nitrogen credit or debit applied based on the identity of the preceding crop. Legume crops generate a positive credit (reduce N recommendation) due to residual biological N fixation. Heavy cereal residues may generate a debit (increase N recommendation) due to temporary immobilisation during decomposition.

Split Application
type: Class
subclass of: Application Timing
comment: A nitrogen management strategy in which the total seasonal nitrogen requirement is divided into two or more separate application events at different growth stages rather than applied as a single dose. Split application is the primary best management practice for improving nitrogen use efficiency: it reduces early-season leaching risk and allows in-season rate adjustment based on crop condition.

Synthetic Fertilizer
type: Class
subclass of: Fertilizer Source
comment: An industrially manufactured fertilizer produced via chemical synthesis (e.g., Haber-Bosch process). Includes solid granular, liquid solution, and gaseous forms.

Tillage
type: Class
subclass of: Management Practice
subclass of: Restriction
  on property: has adjustment
  some values from: Tillage Adjustment
comment: The mechanical manipulation of soil for seedbed preparation, weed control, or residue management. Tillage intensity affects nitrogen dynamics: conventional tillage accelerates residue mineralisation (releasing N), while no-till systems may immobilise surface-applied nitrogen and alter the vertical distribution of nutrients.

Tillage Adjustment
type: Class
subclass of: Nitrogen Adjustment
comment: The nitrogen adjustment applied based on tillage system. No-till and reduced-till systems often require a higher nitrogen rate (debit) because surface residue slows mineralisation and promotes immobilisation, while conventional tillage may earn a credit by accelerating residue breakdown.

Yield Goal
type: Class
subclass of: Fertilization Decision Factor
comment: The target grain or biomass yield used as the primary entry point in yield-goal-based nitrogen recommendation systems (e.g., the K-State recommendation for wheat: N rate = Yield Goal × coefficient − credits). Yield goal is typically set as a realistic attainable yield based on the field's historical performance.

Yield Potential
type: Class
subclass of: Fertilization Decision Factor
comment: The theoretical maximum yield achievable by a cultivar at a given location under non-limiting nutrient, water, and pest conditions. Yield potential sets the upper bound for response-curve-based recommendations; it is a genotype × environment parameter, not a management target.

Atmospheric Nitrogen Deposition
type: Class
subclass of: Nitrogen Supply Source
comment: The transfer of reactive nitrogen from the atmosphere to the soil surface via wet deposition (dissolved in rainfall as NO₃⁻ and NH₄⁺) and dry deposition (gaseous NH₃, NO₂, and particulate nitrogen settling on surfaces). Typically contributes 5–15 kg N/ha/year in agricultural regions; higher near concentrated livestock operations.

Computation Parameter
type: Class
comment: A measurable physiological variable that serves as an input to a nitrogen demand computation. Parameters are linked to their computation via has_parameter; they are NOT types of the computation itself.

Critical Nitrogen Requirement
type: Class
comment: The minimum tissue nitrogen concentration below which crop growth rate begins to decline, expressed as %N on a dry weight basis. The critical concentration decreases as the crop matures (nitrogen dilution curve). When actual tissue N falls below the critical level, nitrogen demand exceeds supply and the crop is nitrogen-limited.

Crop Growth Stage
type: Class
comment: The phenological development stage of the crop at the time of observation, typically described using standardised scales (Feekes, Zadoks, or BBCH for cereals; V/R stages for corn and soybean). Growth stage is the primary determinant of which organs are active nitrogen sinks and how demand is partitioned among them.

Denitrification
type: Class
subclass of: Nitrogen Loss
subclass of: Restriction
  on property: driven by
  some values from: Soil Moisture
subclass of: Restriction
  on property: driven by
  some values from: Soil Temperature
subclass of: Restriction
  on property: driven by
  some values from: Soil pH
subclass of: Restriction
  on property: causes impact
  some values from: Atmospheric Nitrogen Pollution
subclass of: Restriction
  on property: mediated by
  some values from: Denitrifying Organism
comment: The microbial reduction of nitrate (NO₃⁻) to gaseous nitrogen forms (N₂O, N₂) under anaerobic or sub-oxic soil conditions. Performed by facultative anaerobes (Pseudomonas, Bacillus) that use NO₃⁻ as a terminal electron acceptor. The primary gaseous loss pathway in poorly drained, waterlogged, or compacted soils. Also a major source of the greenhouse gas N₂O.

Fixing Organism Group
type: Class
comment: A taxonomic or functional group of microorganisms capable of biological nitrogen fixation. Groups are classified by their fixation mode (symbiotic vs. non-symbiotic) and basic taxonomy (bacteria, cyanobacteria/algae).

Grain Nitrogen Demand
type: Class
subclass of: Organ Nitrogen Demand
subclass of: Restriction
  on property: fulfilled by
  some values from: Nitrogen Translocation
subclass of: Restriction
  on property: has computation
  some values from: Grain Nitrogen Demand Computation
comment: The nitrogen required to fill the developing grain. Grain demand dominates during the reproductive phase (anthesis through physiological maturity). In wheat, 60–80% of grain nitrogen comes from remobilization of pre-anthesis vegetative nitrogen, with the remainder from post-anthesis uptake.

Grain Nitrogen Demand Computation
type: Class
subclass of: Nitrogen Demand Computation
type: NamedIndividual
comment: Computes grain nitrogen demand from seed growth rate and grain nitrogen concentration: Grain_N_Demand = SGR × Grain_N_conc.

Growing Season
type: Class
comment: The period from planting (or emergence) to physiological maturity during which the crop actively grows and accumulates nitrogen. Growing season length and its thermal environment determine the total time window for nitrogen uptake and the cumulative demand.

Leaf Nitrogen Demand
type: Class
subclass of: Organ Nitrogen Demand
subclass of: Restriction
  on property: has computation
  some values from: Leaf Nitrogen Demand Computation
comment: The nitrogen required to support the production and maintenance of photosynthetically active leaf area. Leaf demand is highest during the vegetative phase (tillering through flag leaf in wheat; V6–VT in corn) when the canopy is expanding. Computed from the daily increase in leaf area and the nitrogen content per unit leaf area.

Leaf Nitrogen Demand Computation
type: Class
subclass of: Nitrogen Demand Computation
type: NamedIndividual
comment: Computes leaf nitrogen demand from the daily increase in leaf area index and the nitrogen content per unit leaf area: Leaf_N_Demand = dLAI/dt × N_per_unit_LA.

Mineralization
type: Class
subclass of: Nitrogen Supply Source
subclass of: Restriction
  on property: driven by
  some values from: Soil Moisture
subclass of: Restriction
  on property: driven by
  some values from: Soil Temperature
subclass of: Restriction
  on property: driven by
  some values from: Soil pH
subclass of: Restriction
  on property: has substrate
  some values from: Mineralization Substrate
comment: The microbial conversion of organically bound nitrogen to plant-available mineral forms (NH₄⁺). The dominant pathway for converting soil organic nitrogen into a form crops can absorb. Rate depends on substrate quality (C:N ratio), soil temperature, soil moisture, and pH.

Mineralization Substrate
type: Class
comment: An organic material from which nitrogen is released through microbial mineralization. The C:N ratio of the substrate determines whether net mineralization (N release) or net immobilization (N uptake by microbes) occurs — C:N below approximately 20–25:1 favours net mineralization.

Mobilizable Nitrogen in Leaf
type: Class
subclass of: Nitrogen Pool
comment: The fraction of leaf nitrogen that can be remobilized and translocated to the developing grain during senescence. Comprises primarily Rubisco and other photosynthetic proteins that are degraded as the leaf senesces. Typically 60–80% of total leaf N is mobilizable. Quantified from LAI, green leaf N concentration, and senesced leaf N concentration.

Mobilizable Nitrogen in Stem
type: Class
subclass of: Nitrogen Pool
comment: The fraction of stem nitrogen that can be remobilized and translocated to the developing grain. Stem nitrogen pools are generally smaller than leaf pools but still contribute significantly to grain nitrogen, especially when post-anthesis uptake is limited by drought or nitrogen deficiency.

Nitrate Leaching
type: Class
subclass of: Nitrogen Loss
subclass of: Restriction
  on property: causes impact
  some values from: Nitrogen Accumulation in Water Bodies
subclass of: Restriction
  on property: causes impact
  some values from: Water Pollution
comment: The downward movement of nitrate (NO₃⁻) dissolved in percolating water beyond the crop root zone. The dominant nitrogen loss pathway in well-drained, coarse-textured soils under high rainfall or over-irrigation. Nitrate is the only major nitrogen form subject to leaching because it carries a negative charge and is not retained by cation exchange.

Nitrification
type: Class
subclass of: Nitrogen Transformation
subclass of: Restriction
  on property: driven by
  some values from: Soil Moisture
subclass of: Restriction
  on property: driven by
  some values from: Soil Temperature
subclass of: Restriction
  on property: driven by
  some values from: Soil pH
subclass of: Restriction
  on property: causes impact
  some values from: Soil Acidification
comment: The two-step microbial oxidation of ammonium to nitrate: NH₄⁺ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter). Nitrification converts a relatively immobile, cation-exchange-adsorbed form (NH₄⁺) into a highly mobile anion (NO₃⁻) that is susceptible to both leaching and denitrification. Rate increases with temperature, adequate moisture, and near-neutral pH. This is a transformation, not a supply source — total mineral N is unchanged; only the form changes.

Nitrogen Balance
type: Class
subclass of: Restriction
  on property: has demand
  some values from: Nitrogen Demand
subclass of: Restriction
  on property: has loss
  some values from: Nitrogen Loss
subclass of: Restriction
  on property: has supply
  some values from: Nitrogen Supply
subclass of: Restriction
  on property: has transformation
  some values from: Nitrogen Transformation
comment: The central accounting framework that connects nitrogen supply, demand, transformations, and losses. At any point in time: Soil Available N = (Supply inputs) − (Plant uptake) − (Losses) ± (Transformations that change form but not total pool). Nitrogen Balance serves as the interface between the field-level nitrogen cycle and plant-level nitrogen dynamics.

Nitrogen Demand
type: Class
subclass of: Nitrogen Balance
subclass of: Restriction
  on property: has determinant
  some values from: Critical Nitrogen Requirement
subclass of: Restriction
  on property: has determinant
  some values from: Crop Growth Stage
subclass of: Restriction
  on property: has determinant
  some values from: Nitrogen Uptake
subclass of: Restriction
  on property: modulated by
  some values from: Growing Season
subclass of: Restriction
  on property: modulated by
  some values from: Pest and Disease Pressure
subclass of: Restriction
  on property: modulated by
  some values from: Nutrient
comment: The total quantity of nitrogen required by the crop over a defined period to sustain growth of all organs. Nitrogen demand is the sum of organ-level demands (leaf, stem, root, grain) and is determined by growth rate, tissue nitrogen concentration, and crop growth stage. It represents the 'pull' side of the nitrogen balance.

Nitrogen Demand Computation
type: Class
comment: A mathematical procedure that calculates the nitrogen demand of a specific organ from physiological input parameters. Each computation takes input variables (growth rates, tissue concentrations) and produces a demand estimate in kg N per unit area per time step.

Nitrogen Fixation
type: Class
subclass of: Nitrogen Supply Source
comment: The biological reduction of atmospheric dinitrogen (N₂) to ammonium (NH₃/NH₄⁺) by prokaryotic organisms possessing the nitrogenase enzyme complex. The only biological process that converts inert atmospheric nitrogen into a biologically available form.

Nitrogen Immobilization
type: Class
subclass of: Nitrogen Transformation
comment: The microbial assimilation of mineral nitrogen (NH₄⁺ or NO₃⁻) into organic forms as microorganisms incorporate N into their biomass. Immobilization temporarily removes plant-available N from the soil solution. Dominant when decomposing substrates have high C:N ratios (>25:1). The reverse of mineralization; both processes occur simultaneously, and the balance determines net N release or sequestration.

Nitrogen Loss
type: Class
subclass of: Restriction
  on property: causes impact
  some values from: Soil Degradation
comment: A pathway through which nitrogen is permanently removed from the soil-plant system to the atmosphere or to water bodies. Losses reduce the nitrogen available for crop uptake and represent both an economic cost (wasted fertilizer) and an environmental cost (pollution, greenhouse gas emission).

Nitrogen Pool
type: Class
comment: A compartment within the plant that holds a quantifiable amount of nitrogen at a given time. Pools are distinguished by organ (leaf, stem, root, grain) and by mobility (mobilizable = can be remobilized for translocation to grain; structural = fixed in cell walls and not available for remobilization).

Nitrogen Supply
type: Class
subclass of: Nitrogen Balance
comment: The aggregate of all nitrogen inputs entering the soil-plant system during a defined period. Supply is one side of the nitrogen balance equation; it feeds the Soil Available Nitrogen pool from which plants draw.

Nitrogen Supply Source
type: Class
subclass of: Nitrogen Supply
comment: A specific pathway or mechanism through which nitrogen enters the soil-plant system. Each source represents a genuine input flux — it adds nitrogen that was not previously in the plant-available soil pool.

Nitrogen Transformation
type: Class
comment: A biogeochemical process that converts nitrogen from one chemical form to another within the soil system WITHOUT changing the total nitrogen pool size. Transformations alter the mobility, plant availability, and loss susceptibility of nitrogen but do not represent net gains or losses from the system.

Nitrogen Translocation
type: Class
subclass of: Restriction
  on property: draws from
  some values from: Mobilizable Nitrogen in Leaf
subclass of: Restriction
  on property: draws from
  some values from: Mobilizable Nitrogen in Stem
comment: The physiological process of moving nitrogen from vegetative source organs (leaves and stems) to the developing grain sink during the reproductive phase. Translocation is the primary mechanism by which pre-anthesis nitrogen is reallocated to support grain protein accumulation. In wheat, translocation accounts for 60–80% of final grain nitrogen content.

Nitrogen Uptake
type: Class
subclass of: Restriction
  on property: contributes to
  some values from: Quality Response
subclass of: Restriction
  on property: contributes to
  some values from: Yield Response
subclass of: Restriction
  on property: has determinant
  some values from: Root Growth
comment: The flux of mineral nitrogen (NH₄⁺ and NO₃⁻) from the soil solution into the plant root system. Uptake is the bridge between the soil nitrogen pool and plant nitrogen dynamics: it draws from Soil Available Nitrogen and feeds the Plant Nitrogen Pool. Uptake rate depends on root length density, soil nitrogen concentration, transpiration rate, and crop growth stage.

Non-Mobilizable Leaf Nitrogen
type: Class
subclass of: Nitrogen Pool
comment: The nitrogen remaining in senesced leaf tissue that cannot be remobilized — primarily structural cell-wall nitrogen and residual metabolic nitrogen. This fraction (typically 0.5–1.0% N on a dry weight basis) sets the lower limit of leaf nitrogen concentration at full senescence and determines how much of the total leaf N is recoverable for grain fill.

Non-Symbiotic Fixation
type: Class
subclass of: Nitrogen Fixation
type: NamedIndividual
comment: Nitrogen fixation performed by free-living soil organisms that do not require a host-plant association. Includes aerobic bacteria (Azotobacter), anaerobic bacteria (Clostridium), and photosynthetic cyanobacteria. Contributes relatively small amounts (typically 5–20 kg N/ha/year) compared to symbiotic fixation.

Organ Nitrogen Demand
type: Class
subclass of: Nitrogen Demand
comment: The nitrogen demand of a specific plant organ during its active growth phase. Each organ competes for the nitrogen absorbed by roots; partitioning among organs is regulated by source-sink relationships and crop growth stage.

Pest and Disease Pressure
type: Class
comment: The stress imposed on the crop by pathogens, insects, or weeds that reduces the crop's capacity to utilize nitrogen. Severe foliar disease can destroy photosynthetic tissue, reducing N demand; root diseases impair N uptake; weed competition diverts soil N away from the crop.

Root Nitrogen Demand
type: Class
subclass of: Organ Nitrogen Demand
subclass of: Restriction
  on property: has computation
  some values from: Root Nitrogen Demand Computation
comment: The nitrogen required for root growth and maintenance. Root demand is proportionally highest in early growth stages when the root system is being established. Root nitrogen concentration is typically lower than leaf or grain tissue.

Root Nitrogen Demand Computation
type: Class
subclass of: Nitrogen Demand Computation
comment: Computes root nitrogen demand from root growth rate and root tissue nitrogen concentration.

Soil Available Nitrogen
type: Class
subclass of: Restriction
  on property: depleted by
  some values from: Nitrogen Loss
subclass of: Restriction
  on property: depleted by
  some values from: Nitrogen Uptake
subclass of: Restriction
  on property: supplied through
  some values from: Nitrogen Supply Source
subclass of: Restriction
  on property: quantified by
  some values from: Soil Mineral Nitrogen Content
comment: The pool of plant-available mineral nitrogen (NH₄⁺-N + NO₃⁻-N) in the soil profile at a given time. This is the integrating pool that receives inputs from all supply sources and is depleted by plant uptake and loss pathways. Measured by soil testing (pre-plant or in-season profile nitrate test).

Stem Nitrogen Demand
type: Class
subclass of: Organ Nitrogen Demand
subclass of: Restriction
  on property: has computation
  some values from: Stem Nitrogen Demand Computation
comment: The nitrogen required for stem and structural tissue growth. Stem demand peaks during the stem elongation phase when internodes are extending rapidly. Computed from the daily increase in stem dry matter and the nitrogen concentration per unit stem weight.

Stem Nitrogen Demand Computation
type: Class
subclass of: Nitrogen Demand Computation
type: NamedIndividual
comment: Computes stem nitrogen demand from the daily increase in stem dry matter and the nitrogen concentration per unit stem weight: Stem_N_Demand = dStemDM/dt × N_per_unit_StemW.

Surface Runoff Loss
type: Class
subclass of: Nitrogen Loss
subclass of: Restriction
  on property: causes impact
  some values from: Nitrogen Accumulation in Water Bodies
subclass of: Restriction
  on property: causes impact
  some values from: Water Pollution
comment: The loss of dissolved or sediment-bound nitrogen in water flowing over the soil surface during rainfall or snowmelt. Most significant on sloping land with poor infiltration and where nitrogen fertilizer has been recently surface-applied.

Symbiotic Fixation
type: Class
subclass of: Nitrogen Fixation
type: NamedIndividual
comment: Nitrogen fixation performed by bacteria living in mutualistic association with plant roots, typically within specialized root nodules. The Rhizobium–legume symbiosis is the most important agricultural example, contributing 50–300 kg N/ha/year depending on legume species and growing conditions.

Volatilization
type: Class
subclass of: Nitrogen Loss
subclass of: Restriction
  on property: causes impact
  some values from: Atmospheric Nitrogen Pollution
comment: The loss of nitrogen as gaseous ammonia (NH₃) from the soil surface or plant canopy to the atmosphere. Occurs when ammonium or urea is present at the soil surface under alkaline conditions (pH >7.5), warm temperatures, and wind. Most significant for surface-applied urea and UAN without incorporation. Losses can reach 20–40% of applied N under worst-case conditions.

Crop Response
type: Class
subclass of: Restriction
  on property: observed in response to
  some values from: Nutrient
comment: A measurable agronomic variable observed on a crop to evaluate the effect of a nutrient management treatment. Crop responses are the dependent variables in nutrient-management experiments. Three broad categories are recognised: yield response, growth response, and quality response.

Crop Species
type: Class
comment: The botanical species of the crop being grown. Crop species determines fundamental nutrient requirements, uptake mechanisms, growth habit, and the set of measurable response variables. Cultivar is nested under species.

Cultivar
type: Class
subclass of: Restriction
  on property: has species
  some values from: Crop Species
comment: A named, commercially released variety of a crop species, selected for specific agronomic traits (yield potential, disease resistance, maturity, quality characteristics). Cultivar genotype determines the upper bound of yield response to nitrogen and the grain protein response curve. Each cultivar belongs to exactly one crop species.

Growth Response
type: Class
subclass of: Crop Response
comment: Crop response variables that quantify vegetative development — canopy size, plant stature, organ counts, and root extension. These variables describe the crop's assimilatory capacity and are typically measured non-destructively during the growing season.

Micronutrient
type: Class
subclass of: Nutrient
comment: Essential elements required in very small quantities (typically <100 mg/kg dry matter). Despite low requirements, micronutrient deficiencies can severely limit yield and quality — particularly on high-pH calcareous soils (Fe, Zn, Mn) or sandy leached soils (B, Cu).

Nutrient
type: Class
comment: A chemical element essential for plant growth and development. An element qualifies as a nutrient if its absence prevents the plant from completing its life cycle (Arnon & Stout criteria). This class covers the 14 mineral nutrients managed through soil and fertilizer inputs; structural elements obtained from air and water (C, H, O) are excluded from this management-focused ontology.

Nutrient Form
type: Class
comment: A specific ionic or molecular species of a nutrient as it exists in the soil solution or is taken up by plant roots. Different forms of the same element have distinct mobility, plant availability, and loss-pathway characteristics. For example, nitrate-nitrogen (NO₃⁻-N) is highly mobile and leachable, while ammonium-nitrogen (NH₄⁺-N) is adsorbed on cation exchange sites.

Nutrient Use Efficiency
type: Class
subclass of: Crop Response
comment: A metric that quantifies the relationship between nutrient input and crop output. NUE integrates the effectiveness of the entire nutrient management system — soil supply, fertilizer recovery, and internal plant utilisation. Multiple definitions exist; the three most widely used in agronomic research are modeled as individuals.

Primary Mineral Nutrient
type: Class
subclass of: Nutrient
comment: Macronutrients required by plants in the largest quantities (typically >0.1% of dry matter) and most frequently limiting in agricultural systems. The primary mineral nutrients are nitrogen (N), phosphorus (P), and potassium (K) — the three elements represented on every fertilizer grade label.

Quality Response
type: Class
subclass of: Crop Response
comment: Crop response variables that quantify the end-use or market quality of harvested grain. In wheat, quality is primarily determined by protein concentration and its functional properties for milling and baking. Quality often responds to nitrogen rate at rates above those needed for maximum yield.

Secondary Mineral Nutrient
type: Class
subclass of: Nutrient
comment: Macronutrients required in moderate quantities (typically 0.01–0.5% of dry matter). Less frequently limiting than N-P-K but increasingly important as yield levels rise and soil reserves are depleted. Includes calcium (Ca), magnesium (Mg), and sulfur (S).

Soil Toxicity Factor
type: Class
comment: A soil chemical constituent that becomes harmful to plant growth when present at elevated concentrations. Toxicity factors are not essential nutrients; they are managed by adjusting soil conditions (e.g., liming to raise pH and reduce aluminum solubility).

Wheat Quality Measure
type: Class
subclass of: Quality Response
comment: End-use quality variables specific to wheat milling and baking. These parameters determine the functional properties of flour and the suitability of grain for different market classes (hard red winter, hard red spring, soft wheat). Strongly influenced by nitrogen rate and timing, particularly late-season applications at or after flag leaf.

Wheat Yield Component
type: Class
subclass of: Yield Response
comment: Yield component variables specific to wheat (Triticum spp.) and related small-grain cereals. These decompose grain yield into its agronomic determinants: spikes per area, spikelets per spike, grains per spikelet, and individual grain weight.

Yield Response
type: Class
subclass of: Crop Response
comment: Crop response variables that quantify harvestable product or its components. Includes both the final grain yield and the yield components that explain how yield is assembled (e.g., spike number × grains per spike × grain weight).

Maturity Group
type: Class
comment: A classification of wheat cultivar maturity relative to the range of commercial varieties grown in the region. Maturity affects the timing of anthesis and grain fill, which in turn determines the optimal nitrogen application window and the duration of exposure to disease pressure.

Nitrogen Timing Split
type: Class
comment: A specific allocation of the total nitrogen rate across application windows (fall, spring, anthesis), expressed as percentages that sum to 100. For example, '40/60/0' means 40% of total N applied in fall, 60% in spring, 0% at anthesis. Split applications are the primary best management practice for matching nitrogen supply to crop demand.

Plot Observation
type: Class
subclass of: Restriction
  on property: observed at site-year
  some values from: Site-Year Environment
subclass of: Restriction
  on property: observed cultivar
  some values from: Cultivar
subclass of: Restriction
  on property: observed previous crop
  some values from: Previous Crop
comment: A single observation record from a field trial, corresponding to one plot in one site-year. This is the binding concept that connects the experimental context (where, when, which trial), the treatments applied (nitrogen rate, variety, timing split), and the measurements recorded (yield, protein, test weight, biomass, yield components). Each row in a field trial dataset corresponds to one Plot Observation individual.

Site-Year Environment
type: Class
comment: A composite identifier representing a unique combination of location and crop-season year (e.g., 'HUT18' = Hutchinson 2017-18). The site-year environment is the standard agronomic unit for multi-environment trial analysis. It captures the unreplicated environmental variation (weather, soil background) that all plots at that location-year share.

Treatment Factor
type: Class
comment: A named experimental factor in a factorial trial design. Each factor has a name (e.g., 'Fertility') and a level description (e.g., 'N rate'). Up to three factors may be combined in a single trial. Treatment 1 is the primary factor (Fertility or Management), Treatment 2 is always Variety, and Treatment 3 is an optional secondary factor (N timing split or Plant Growth Regulator).

Atmospheric Nitrogen Pollution
type: Class
subclass of: Environmental Impact
comment: The release of reactive nitrogen gases to the atmosphere from agricultural sources. Includes ammonia (NH₃) from volatilization (contributing to particulate matter formation and acid deposition downwind) and nitrous oxide (N₂O) from denitrification and nitrification (a potent greenhouse gas with a global warming potential approximately 265 times that of CO₂ over 100 years).

Denitrifying Organism
type: Class
comment: A microorganism capable of performing denitrification — the anaerobic reduction of nitrate (NO₃⁻) or nitrite (NO₂⁻) to gaseous nitrogen forms (N₂O, N₂). Denitrifiers are primarily facultative anaerobes that switch from aerobic respiration to nitrate respiration when oxygen is depleted. They are taxonomically diverse, spanning multiple bacterial genera. This class parallels Fixing_Organism_Group in the nitrogen module but represents a different functional role.

Environmental Impact
type: Class
comment: An adverse consequence for the natural environment resulting from nitrogen losses or transformations in the agricultural system. Environmental impacts are the externalities of nitrogen management — costs borne by ecosystems, water resources, or the atmosphere when nitrogen escapes the intended soil-plant pathway. Each impact is linked to the specific loss or transformation process that causes it.

Nitrogen Accumulation in Water Bodies
type: Class
subclass of: Water Pollution
comment: The progressive enrichment of surface waters (lakes, rivers, estuaries, coastal zones) with reactive nitrogen, leading to eutrophication — excessive algal growth, oxygen depletion (hypoxia), fish kills, and loss of aquatic biodiversity. The Gulf of Mexico hypoxic zone is a large-scale example driven primarily by agricultural nitrate from the Mississippi River basin.

Root Growth
type: Class
comment: The development and extension of the crop root system through the soil profile. Root growth determines the volume of soil explored for nitrogen and the density of root length available for nutrient absorption. Root architecture, depth, and branching are influenced by soil physical conditions (compaction, drainage), nutrient distribution, and crop species/genotype. Root growth is a primary determinant of nitrogen uptake capacity.

Soil Acidification
type: Class
subclass of: Environmental Impact
comment: The decrease in soil pH caused by the release of hydrogen ions (H⁺) during nitrification: each mole of NH₄⁺ oxidised to NO₃⁻ releases two moles of H⁺. Repeated application of ammonium-based fertilizers (urea, anhydrous ammonia, ammonium sulfate) without compensatory liming progressively acidifies the soil, reducing nutrient availability and increasing aluminum toxicity risk. Note: this impact is caused by NITRIFICATION (a transformation), not by denitrification.

Soil Degradation
type: Class
subclass of: Environmental Impact
comment: The deterioration of soil physical, chemical, or biological properties resulting from chronic nitrogen mismanagement. Includes long-term acidification, depletion of soil organic matter through accelerated mineralization, structural decline, and loss of microbial diversity. A cumulative, slow-onset impact that reduces the soil's long-term productive capacity.

Soil Mineral Nitrogen Content
type: Class
comment: The measured concentration or mass of plant-available mineral nitrogen (NH₄⁺-N + NO₃⁻-N) in the soil profile at a specific time, expressed in mg/kg (ppm) or kg N/ha to a defined depth. This is the quantifiable, laboratory-measured expression of the Soil Available Nitrogen pool defined in the nitrogen module. Measured by KCl extraction and colorimetric analysis; the basis for profile-based nitrogen recommendations (e.g., the pre-plant soil nitrate test used in the Great Plains).

Water Pollution
type: Class
subclass of: Environmental Impact
comment: The degradation of surface water or groundwater quality by elevated concentrations of reactive nitrogen (primarily nitrate). Groundwater contamination occurs when nitrate leaches below the root zone and reaches aquifers; the US EPA maximum contaminant level for drinking water is 10 mg NO₃-N/L. Surface water contamination occurs via runoff and subsurface drainage.

Alabama
type: NamedIndividual
type: State
has FIPS code: 01
comment: Alabama (AL). FIPS code 01.

Alaska
type: NamedIndividual
type: State
has FIPS code: 02
comment: Alaska (AK). FIPS code 02.

Arizona
type: NamedIndividual
type: State
has FIPS code: 04
comment: Arizona (AZ). FIPS code 04.

Arkansas
type: NamedIndividual
type: State
has FIPS code: 05
comment: Arkansas (AR). FIPS code 05. Part of the US Drought Monitor study area.

California
type: NamedIndividual
type: State
has FIPS code: 06
comment: California (CA). FIPS code 06.

Clay
type: NamedIndividual
type: Soil Texture
comment: ≥40 % clay with ≤45 % sand and ≤40 % silt. Highest CEC and nutrient retention of all textural classes; very slow permeability and high shrink-swell potential make tillage timing critical.

Clay Loam
type: NamedIndividual
type: Soil Texture
comment: 27–40 % clay with 20–45 % sand. High CEC and nutrient retention; moderate drainage that reduces nitrate leaching but may impede root growth when compacted.

Colorado
type: NamedIndividual
type: State
has FIPS code: 08
comment: Colorado (CO). FIPS code 08. Part of the US Drought Monitor study area.

Connecticut
type: NamedIndividual
type: State
has FIPS code: 09
comment: Connecticut (CT). FIPS code 09.

Delaware
type: NamedIndividual
type: State
has FIPS code: 10
comment: Delaware (DE). FIPS code 10.

0–15 cm (Surface)
type: NamedIndividual
type: Sampling Depth
has lower depth (cm): 15.0
has upper depth (cm): 0.0
comment: The standard surface sampling depth used in most routine soil fertility testing (≈0–6 inches). Captures the zone of greatest biological activity, organic matter concentration, and fertilizer incorporation.

0–30 cm (Plough Layer)
type: NamedIndividual
type: Sampling Depth
has lower depth (cm): 30.0
has upper depth (cm): 0.0
comment: The full plough-layer depth (≈0–12 inches). Represents the zone most affected by tillage and surface-applied amendments; standard for international soil carbon and nutrient inventories.

15–45 cm (Sub-Surface)
type: NamedIndividual
type: Sampling Depth
has lower depth (cm): 45.0
has upper depth (cm): 15.0
comment: A common sub-surface interval (≈6–18 inches) used to assess nutrient status below the plough layer, particularly residual nitrate-nitrogen for profile nitrogen budgeting.

15–60 cm (Sub-Surface)
type: NamedIndividual
type: Sampling Depth
has lower depth (cm): 60.0
has upper depth (cm): 15.0
comment: An extended sub-surface interval (≈6–24 inches) often used in deep-soil nitrogen sampling programs in semi-arid regions to account for nitrate that has moved below the root zone.

60–90 cm (Deep Sub-Soil)
type: NamedIndividual
type: Sampling Depth
has lower depth (cm): 90.0
has upper depth (cm): 60.0
comment: A deep sub-soil interval (≈24–36 inches) sampled to evaluate deep leaching of mobile nutrients (primarily nitrate) and to assess subsoil constraints such as compaction or salinity.

Excessively Drained
type: NamedIndividual
type: Soil Drainage Class
comment: Water is removed from the soil very rapidly. The water table is rarely or never observed. Common in coarse sands and gravels. Very high nitrate leaching risk; nutrients move below the root zone quickly after rain or irrigation.

Florida
type: NamedIndividual
type: State
has FIPS code: 12
comment: Florida (FL). FIPS code 12.

Georgia
type: NamedIndividual
type: State
has FIPS code: 13
comment: Georgia (GA). FIPS code 13.

Hawaii
type: NamedIndividual
type: State
has FIPS code: 15
comment: Hawaii (HI). FIPS code 15.

Idaho
type: NamedIndividual
type: State
has FIPS code: 16
comment: Idaho (ID). FIPS code 16.

Illinois
type: NamedIndividual
type: State
has FIPS code: 17
comment: Illinois (IL). FIPS code 17.

Indiana
type: NamedIndividual
type: State
has FIPS code: 18
comment: Indiana (IN). FIPS code 18.

Iowa
type: NamedIndividual
type: State
has FIPS code: 19
comment: Iowa (IA). FIPS code 19. Part of the US Drought Monitor study area.

Kansas
type: NamedIndividual
type: State
has FIPS code: 20
comment: Kansas (KS). FIPS code 20. Part of the US Drought Monitor study area and the primary site of GRIP field trials.

Kentucky
type: NamedIndividual
type: State
has FIPS code: 21
comment: Kentucky (KY). FIPS code 21.

Loam
type: NamedIndividual
type: Soil Texture
comment: A balanced mixture of sand (23–52 %), silt (28–50 %), and clay (7–27 %). Often regarded as the ideal agricultural soil: good drainage, aeration, water retention, and nutrient-holding capacity.

Loamy Sand
type: NamedIndividual
type: Soil Texture
comment: 70–90 % sand with silt + 1.5× clay between 15 and 30. Slightly better water retention than sand but still highly permeable; requires frequent, light nutrient applications.

Louisiana
type: NamedIndividual
type: State
has FIPS code: 22
comment: Louisiana (LA). FIPS code 22.

Maine
type: NamedIndividual
type: State
has FIPS code: 23
comment: Maine (ME). FIPS code 23.

Maryland
type: NamedIndividual
type: State
has FIPS code: 24
comment: Maryland (MD). FIPS code 24.

Massachusetts
type: NamedIndividual
type: State
has FIPS code: 25
comment: Massachusetts (MA). FIPS code 25.

Michigan
type: NamedIndividual
type: State
has FIPS code: 26
comment: Michigan (MI). FIPS code 26.

Minnesota
type: NamedIndividual
type: State
has FIPS code: 27
comment: Minnesota (MN). FIPS code 27.

Mississippi
type: NamedIndividual
type: State
has FIPS code: 28
comment: Mississippi (MS). FIPS code 28.

Missouri
type: NamedIndividual
type: State
has FIPS code: 29
comment: Missouri (MO). FIPS code 29. Part of the US Drought Monitor study area.

Moderately Well Drained
type: NamedIndividual
type: Soil Drainage Class
comment: Water is removed somewhat slowly; the soil is wet at shallow depth for short periods during the growing season. Faint mottles may be present. Moderate risk of temporary anaerobic conditions that can trigger denitrification after heavy rainfall.

Montana
type: NamedIndividual
type: State
has FIPS code: 30
comment: Montana (MT). FIPS code 30.

Nebraska
type: NamedIndividual
type: State
has FIPS code: 31
comment: Nebraska (NE). FIPS code 31. Part of the US Drought Monitor study area.

Nevada
type: NamedIndividual
type: State
has FIPS code: 32
comment: Nevada (NV). FIPS code 32.

New Hampshire
type: NamedIndividual
type: State
has FIPS code: 33
comment: New Hampshire (NH). FIPS code 33.

New Jersey
type: NamedIndividual
type: State
has FIPS code: 34
comment: New Jersey (NJ). FIPS code 34.

New Mexico
type: NamedIndividual
type: State
has FIPS code: 35
comment: New Mexico (NM). FIPS code 35.

New York
type: NamedIndividual
type: State
has FIPS code: 36
comment: New York (NY). FIPS code 36.

North Carolina
type: NamedIndividual
type: State
has FIPS code: 37
comment: North Carolina (NC). FIPS code 37.

North Dakota
type: NamedIndividual
type: State
has FIPS code: 38
comment: North Dakota (ND). FIPS code 38.

Ohio
type: NamedIndividual
type: State
has FIPS code: 39
comment: Ohio (OH). FIPS code 39.

Oklahoma
type: NamedIndividual
type: State
has FIPS code: 40
comment: Oklahoma (OK). FIPS code 40. Part of the US Drought Monitor study area.

Oregon
type: NamedIndividual
type: State
has FIPS code: 41
comment: Oregon (OR). FIPS code 41.

Pennsylvania
type: NamedIndividual
type: State
has FIPS code: 42
comment: Pennsylvania (PA). FIPS code 42.

Poorly Drained
type: NamedIndividual
type: Soil Drainage Class
comment: Water is removed so slowly that the soil is wet at shallow depth for long periods. A seasonally high water table limits root depth and creates strongly reducing conditions. Significant nitrogen losses via denitrification; phosphorus mobilization risk increases under sustained anaerobic conditions.

Rhode Island
type: NamedIndividual
type: State
has FIPS code: 44
comment: Rhode Island (RI). FIPS code 44.

Sand
type: NamedIndividual
type: Soil Texture
comment: ≥85 % sand with the percentage of silt plus 1.5× the percentage of clay ≤15. Very high permeability, very low water and nutrient retention; highest leaching risk for mobile nutrients like nitrate.

Sandy Clay
type: NamedIndividual
type: Soil Texture
comment: ≥35 % clay and ≥45 % sand. Unusual combination; high shrink-swell with relatively rapid macropore drainage. Nutrient retention is high but physical management is challenging.

Sandy Clay Loam
type: NamedIndividual
type: Soil Texture
comment: 20–35 % clay, <28 % silt, and ≥45 % sand. Moderate shrink-swell potential; balances drainage and retention but can be difficult to work when wet.

Sandy Loam
type: NamedIndividual
type: Soil Texture
comment: 43–85 % sand with moderate silt and clay. Good drainage with moderate water-holding capacity; widely considered productive agricultural soil with manageable leaching risk.

Silt
type: NamedIndividual
type: Soil Texture
comment: ≥80 % silt and ≤12 % clay. Very high water-holding capacity but prone to compaction and poor aeration; rare in agricultural classification.

Silt Loam
type: NamedIndividual
type: Soil Texture
comment: ≥50 % silt with 12–27 % clay, or 50–80 % silt with <12 % clay. High water-holding capacity and fertility; susceptible to surface crusting and erosion when exposed.

Silty Clay
type: NamedIndividual
type: Soil Texture
comment: ≥40 % clay and ≥40 % silt. Very high CEC and water retention; slow permeability creates anaerobic micro-sites that promote denitrification losses of applied nitrogen.

Silty Clay Loam
type: NamedIndividual
type: Soil Texture
comment: 27–40 % clay and ≥40 % silt. Excellent nutrient and water retention; common in fertile alluvial plains but slow to drain and prone to waterlogging.

Somewhat Excessively Drained
type: NamedIndividual
type: Soil Drainage Class
comment: Water is removed rapidly. Soils are sandy or have very high hydraulic conductivity. Nutrient leaching risk is high but slightly less than excessively drained soils due to marginally greater water retention.

Somewhat Poorly Drained
type: NamedIndividual
type: Soil Drainage Class
comment: Water is removed slowly enough that the soil is wet at shallow depth for significant periods during the growing season. Distinct mottling is common. Increased potential for denitrification losses and reduced root zone aeration.

South Carolina
type: NamedIndividual
type: State
has FIPS code: 45
comment: South Carolina (SC). FIPS code 45.

South Dakota
type: NamedIndividual
type: State
has FIPS code: 46
comment: South Dakota (SD). FIPS code 46.

Tennessee
type: NamedIndividual
type: State
has FIPS code: 47
comment: Tennessee (TN). FIPS code 47.

Texas
type: NamedIndividual
type: State
has FIPS code: 48
comment: Texas (TX). FIPS code 48.

Utah
type: NamedIndividual
type: State
has FIPS code: 49
comment: Utah (UT). FIPS code 49.

Vermont
type: NamedIndividual
type: State
has FIPS code: 50
comment: Vermont (VT). FIPS code 50.

Very Poorly Drained
type: NamedIndividual
type: Soil Drainage Class
comment: Water is removed so slowly that free water remains at or near the surface most of the year. Typical of depressional areas and bogs. Crop production requires artificial drainage. Denitrification is the dominant nitrogen loss pathway; organic matter accumulates due to suppressed decomposition.

Virginia
type: NamedIndividual
type: State
has FIPS code: 51
comment: Virginia (VA). FIPS code 51.

Washington
type: NamedIndividual
type: State
has FIPS code: 53
comment: Washington (WA). FIPS code 53.

Well Drained
type: NamedIndividual
type: Soil Drainage Class
comment: Water is removed readily but not rapidly. The soil profile is free of mottling related to wetness. Considered optimal for most agricultural crops; supports aerobic conditions favouring nitrification and good root development.

West Virginia
type: NamedIndividual
type: State
has FIPS code: 54
comment: West Virginia (WV). FIPS code 54.

Wisconsin
type: NamedIndividual
type: State
has FIPS code: 55
comment: Wisconsin (WI). FIPS code 55.

Wyoming
type: NamedIndividual
type: State
has FIPS code: 56
comment: Wyoming (WY). FIPS code 56.

Ammonium Nitrate
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 34.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: NH₄NO₃ (34-0-0). Supplies nitrogen in both ammonium and nitrate forms, providing immediate nitrate availability and slower ammonium release. Lower volatilisation risk than urea. Subject to regulatory restrictions in some regions due to security concerns.

Ammonium Polyphosphate
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 10.0
has P₂O₅ percent: 34.0
has S percent: 0.0
comment: APP (10-34-0). A liquid phosphorus fertilizer used in starter bands and fertigation. Contains 10% nitrogen as incidental ammonium. The polyphosphate form provides extended phosphorus availability through gradual hydrolysis.

Ammonium Sulfate
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 21.0
has P₂O₅ percent: 0.0
has S percent: 24.0
comment: (NH₄)₂SO₄ (21-0-0-24S). Supplies both nitrogen and sulfur. Preferred on sulfur-deficient soils and for crops with high sulfur demand (canola, alfalfa). Acidifying effect makes it useful for high-pH soils.

Anhydrous Ammonia
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 82.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: NH₃ applied as a pressurised liquid that becomes gas on release (82-0-0). The most concentrated and generally least-cost nitrogen source per unit N. Requires sub-surface injection to prevent gaseous loss; temporarily sterilises a narrow zone around the injection point.

At Planting
type: NamedIndividual
type: Application Timing
comment: Nitrogen applied concurrently with sowing, often as a starter band near the seed. Provides immediate nitrogen to support seedling vigour and early canopy development.

Banding
type: NamedIndividual
type: Application Method
comment: Concentrated placement of fertilizer in narrow bands, typically near the seed row at planting. Increases nutrient concentration in the root zone, improving early-season uptake efficiency and reducing fixation in high-phosphorus-fixing soils.

Broadcast
type: NamedIndividual
type: Application Method
comment: Uniform surface spreading of fertilizer across the entire field area. Simplest method with highest coverage but exposes granular or liquid material to volatilisation and immobilisation at the surface unless incorporated by tillage or rainfall.

Calcium Nitrate
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 15.5
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: Ca(NO₃)₂ (15.5-0-0). Supplies nitrogen entirely as nitrate with supplemental calcium. Non-acidifying; used on acid-sensitive soils and in fertigation for high-value crops.

Cereals
type: NamedIndividual
type: Crop Category
comment: Grass-family grain crops (wheat, corn, sorghum, barley, rice, oats). Cereal residues typically have high C:N ratios (40–80:1), causing net nitrogen immobilisation during early decomposition. Following a cereal crop, the nitrogen recommendation is often increased to offset this temporary immobilisation.

Compost
type: NamedIndividual
type: Organic Nutrient Source
has K₂O percent: 0.0
has N percent: 0.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: Aerobically decomposed organic matter with stable humus-like properties. Nitrogen availability in the year of application is typically low (5–20% of total N) because most nitrogen has been stabilised during composting. Primary value is in soil organic matter building and long-term nutrient supply.

Di-Ammonium Phosphate
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 18.0
has P₂O₅ percent: 46.0
has S percent: 0.0
comment: DAP (NH₄)₂HPO₄ (18-46-0). The most widely used phosphorus fertilizer. Applied primarily to meet crop phosphorus requirements; the 18% nitrogen is an incidental contribution that must be credited when computing the total nitrogen budget.

Fallow
type: NamedIndividual
type: Crop Category
comment: A period in which no crop is grown and the field is left idle. Mineralisation continues during fallow, accumulating nitrate in the profile. Soil nitrate testing after fallow typically shows elevated residual nitrogen that should be credited against the recommendation.

Fertigation
type: NamedIndividual
type: Application Method
comment: Application of soluble fertilizer through the irrigation system (drip, pivot, or sprinkler). Allows frequent, low-dose delivery synchronised with crop water uptake; ideal for split nitrogen programmes and high-value crops.

Flag Leaf
type: NamedIndividual
type: Application Timing
comment: Late-season nitrogen application at or near flag leaf emergence in cereals (Feekes 8–9). Targets grain protein content rather than additional yield; the dominant timing for quality-driven nitrogen in hard red winter wheat.

Foliar Application
type: NamedIndividual
type: Application Method
comment: Spraying a dilute fertilizer solution directly onto crop foliage. Used for supplemental nitrogen (typically UAN) when soil uptake is limited or for rapid correction of deficiency. Total N per pass is constrained by leaf burn thresholds.

Incorporation
type: NamedIndividual
type: Application Method
comment: Mechanical mixing of surface-applied fertilizer into the topsoil by tillage (disc, field cultivator) shortly after application. Reduces ammonia volatilisation from urea and UAN; typically performed within 24–48 hours of surface broadcast.

Injection
type: NamedIndividual
type: Application Method
comment: Sub-surface placement of liquid or gaseous fertilizer (e.g., anhydrous ammonia, UAN) into the soil using knife or coulter openers. Eliminates surface volatilisation; the mandatory method for anhydrous ammonia.

Legumes
type: NamedIndividual
type: Crop Category
comment: Crops in the Fabaceae family (soybean, pea, lentil, alfalfa, clover) that form symbiotic associations with Rhizobium bacteria to fix atmospheric nitrogen. Legume residues have low C:N ratios (15–25:1) and release a nitrogen credit to the succeeding crop, typically 20–60 kg N/ha depending on species and biomass.

Manure
type: NamedIndividual
type: Organic Nutrient Source
has K₂O percent: 0.0
has N percent: 0.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: Animal excrement (cattle, poultry, swine) applied as a nutrient source. Nitrogen content varies widely (typically 1–5% dry weight) depending on species, diet, and handling. A fraction of total N is available in the year of application (typically 40–75% for poultry, 25–50% for cattle); the remainder mineralises over subsequent seasons. N% here is set to 0 as a placeholder — actual values must come from laboratory analysis of the specific manure.

Mono-Ammonium Phosphate
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 11.0
has P₂O₅ percent: 52.0
has S percent: 0.0
comment: MAP NH₄H₂PO₄ (11-52-0). A high-analysis phosphorus starter fertilizer. The 11% nitrogen is incidental and should be credited in the nitrogen budget. Lower ammonia toxicity risk than DAP, making it safer as a seed-placed fertilizer.

Oilseeds
type: NamedIndividual
type: Crop Category
comment: Non-legume broadleaf crops grown primarily for oil (canola, sunflower, safflower). Residue C:N ratios and nitrogen credits are intermediate between cereals and legumes.

Polymer-Coated Urea
type: NamedIndividual
type: Enhanced Efficiency Fertilizer
has K₂O percent: 0.0
has N percent: 44.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: Urea granules encapsulated in a semi-permeable polymer membrane that controls the rate of nitrogen release based on soil temperature and moisture. Designed to match nitrogen supply to crop demand over the growing season, reducing the need for split applications.

Pre-Plant
type: NamedIndividual
type: Application Timing
comment: Nitrogen applied before planting or sowing, typically during seedbed preparation. The entire dose resides in the soil before crop roots are active, maximising exposure to early-season leaching and denitrification. Often combined with incorporation.

Side-Dress
type: NamedIndividual
type: Application Method
comment: Post-emergence application of nitrogen alongside growing crop rows, typically by surface band or shallow injection. The primary in-season method for row crops (corn, sorghum); allows the rate to be adjusted based on early-season observations.

Topdress
type: NamedIndividual
type: Application Timing
comment: In-season surface application to standing crop, typically at tillering or stem elongation in cereals. Allows rate adjustment based on observed crop condition, tiller density, or sensor readings.

Urea
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 46.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: CO(NH₂)₂. The most widely used dry nitrogen fertilizer globally (46-0-0). High N concentration minimises transport and storage costs. Subject to volatilisation losses when surface-applied without incorporation; urease inhibitors (NBPT) mitigate this.

Urea Ammonium Nitrate
type: NamedIndividual
type: Synthetic Fertilizer
has K₂O percent: 0.0
has N percent: 32.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: A liquid solution of urea and ammonium nitrate, typically 28-0-0 or 32-0-0. Combines three forms of nitrogen (urea, ammonium, nitrate), providing both immediate and short-term availability. Widely used in fertigation and foliar programmes.

Urea with DCD Nitrification Inhibitor
type: NamedIndividual
type: Enhanced Efficiency Fertilizer
has K₂O percent: 0.0
has N percent: 46.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: Urea combined with dicyandiamide (DCD), a nitrification inhibitor that slows the conversion of ammonium to nitrate in the soil. Reduces nitrate leaching and nitrous oxide (N₂O) emissions by keeping nitrogen in the less mobile ammonium form for longer.

Urea with NBPT Urease Inhibitor
type: NamedIndividual
type: Enhanced Efficiency Fertilizer
has K₂O percent: 0.0
has N percent: 46.0
has P₂O₅ percent: 0.0
has S percent: 0.0
comment: Urea treated with N-(n-butyl)thiophosphoric triamide (NBPT), a urease inhibitor that delays the hydrolysis of urea to ammonium, reducing ammonia volatilisation by 40–70% compared to untreated urea. Effective window is typically 7–14 days after application.

Azotobacter
type: NamedIndividual
type: Fixing Organism Group
associated with: Non-Symbiotic Fixation
comment: A genus of free-living, aerobic, heterotrophic bacteria capable of fixing atmospheric nitrogen. Found in neutral to alkaline soils; sensitive to low pH and waterlogging. Fixes 10–20 kg N/ha/year under favourable conditions.

Clostridium
type: NamedIndividual
type: Fixing Organism Group
associated with: Non-Symbiotic Fixation
comment: A genus of anaerobic, spore-forming bacteria that fix nitrogen in waterlogged or oxygen-depleted soil microsites. Less efficient than aerobic fixers but active in conditions where Azotobacter cannot function.

Crop Residue
type: NamedIndividual
type: Mineralization Substrate
comment: Above- and below-ground plant material remaining in the field after harvest. Residue nitrogen availability depends on the C:N ratio of the material: low-C:N legume residues release nitrogen within weeks, while high-C:N cereal straw can immobilize nitrogen for several months before net release.

Cyanobacteria
type: NamedIndividual
type: Fixing Organism Group
associated with: Non-Symbiotic Fixation
comment: Photosynthetic prokaryotes (formerly called blue-green algae) that fix nitrogen using specialized cells (heterocysts) in filamentous genera (Anabaena, Nostoc). Particularly important in flooded rice systems where they can contribute 20–40 kg N/ha/season.

Daily Increase in Leaf Area Index
type: NamedIndividual
type: Computation Parameter
is parameter of: Leaf Nitrogen Demand Computation
comment: The rate of change of leaf area index per day (m²/m²/day). Drives leaf nitrogen demand during canopy expansion phases.

Daily Increase in Stem Dry Matter
type: NamedIndividual
type: Computation Parameter
is parameter of: Stem Nitrogen Demand Computation
comment: The rate of stem dry matter accumulation per day (g/m²/day). Drives stem nitrogen demand during the stem elongation phase.

Grain Nitrogen Concentration
type: NamedIndividual
type: Computation Parameter
is parameter of: Grain Nitrogen Demand Computation
comment: The nitrogen concentration in the developing grain (% N on a dry weight basis). Determines both grain protein content (for quality) and the nitrogen requirement per unit of grain dry matter produced. Typically 1.8–2.5% N for wheat.

Nitrogen Concentration in Green Leaf
type: NamedIndividual
type: Computation Parameter
comment: The nitrogen concentration of actively photosynthesizing leaf tissue (% N dry weight). Together with LAI, determines the total nitrogen content of the green canopy from which mobilizable N is calculated.

Nitrogen Concentration in Senesced Leaf
type: NamedIndividual
type: Computation Parameter
comment: The residual nitrogen concentration in fully senesced leaf tissue (% N dry weight). Represents the non-mobilizable fraction; the difference between green leaf N and senesced leaf N quantifies the mobilizable pool.

Nitrogen Content Per Unit Leaf Area
type: NamedIndividual
type: Computation Parameter
is parameter of: Leaf Nitrogen Demand Computation
comment: The mass of nitrogen per unit of one-sided leaf area (g N/m² leaf). Reflects the photosynthetic nitrogen investment in the canopy; varies with leaf age and canopy position.

Nitrogen Content Per Unit Stem Weight
type: NamedIndividual
type: Computation Parameter
is parameter of: Stem Nitrogen Demand Computation
comment: The concentration of nitrogen per unit of stem dry weight (g N/g DM or %). Typically lower than leaf N concentration and declines as the stem matures.

Rhizobium
type: NamedIndividual
type: Fixing Organism Group
associated with: Symbiotic Fixation
comment: A collective term for the genera of root-nodulating bacteria (Rhizobium, Bradyrhizobium, Sinorhizobium, Mesorhizobium) that form symbiotic nitrogen-fixing associations with legume crops. The agronomically most significant group of nitrogen fixers.

Seed Growth Rate
type: NamedIndividual
type: Computation Parameter
is parameter of: Grain Nitrogen Demand Computation
comment: The rate of dry matter accumulation in the developing grain (mg/grain/day or g/m²/day). Determined by the duration and rate of grain fill, which are influenced by temperature, nitrogen supply, and source capacity.

Soil Organic Matter
type: NamedIndividual
type: Mineralization Substrate
comment: The stable pool of decomposed organic material in the soil. Releases nitrogen slowly through ongoing mineralization; typically contributes 1–3% of its total N per year. The largest single source of plant-available nitrogen in unfertilized systems.

Total Nitrogen in Stem
type: NamedIndividual
type: Computation Parameter
comment: The total mass of nitrogen in stem tissue at a given growth stage (kg N/ha). The starting point for calculating the mobilizable fraction in the stem, which depends on structural versus metabolic nitrogen partitioning.

Aboveground Biomass
type: NamedIndividual
type: Yield Response
comment: The total dry matter of all aboveground plant parts at a specified growth stage, expressed in kg/ha or t/ha. Used to assess total crop productivity and to calculate harvest index and nitrogen uptake.

Agronomic Efficiency
type: NamedIndividual
type: Nutrient Use Efficiency
comment: AE = (Yield_fertilised − Yield_unfertilised) / N_applied. Expressed in kg grain per kg N applied. Measures the yield gain per unit of fertilizer nitrogen. The most intuitive and commonly reported NUE metric; combines soil supply, fertilizer recovery, and internal utilisation into a single number.

Aluminum
type: NamedIndividual
type: Soil Toxicity Factor
comment: Element Al. Not a plant nutrient. Aluminum toxicity is the primary growth-limiting factor on acid soils (pH <5.5) worldwide. Soluble Al³⁺ inhibits root elongation, reduces phosphorus availability, and impairs calcium and magnesium uptake. Managed by liming to maintain soil pH above 5.5–6.0.

Ammonium Nitrogen
type: NamedIndividual
type: Nutrient Form
is form of: Nitrogen
comment: NH₄⁺-N. The reduced, cationic form of soil mineral nitrogen. Adsorbed on cation exchange sites and therefore resistant to leaching. Converted to nitrate by nitrifying bacteria (Nitrosomonas, Nitrobacter) under aerobic, warm conditions. Preferred uptake form for rice and some acid-tolerant species.

Boron
type: NamedIndividual
type: Micronutrient
comment: Element B. Essential for cell wall formation, pollen viability, and sugar transport. Has the narrowest range between deficiency and toxicity of all micronutrients. Critical for reproductive development in canola, alfalfa, and sunflower.

Calcium
type: NamedIndividual
type: Secondary Mineral Nutrient
comment: Element Ca. Structural component of cell walls (calcium pectate), involved in cell division and membrane stability. Deficiency is rare in field crops but critical in horticultural systems (blossom-end rot in tomato). Soil calcium is closely tied to pH and liming practices.

Canola
type: NamedIndividual
type: Crop Species
comment: Brassica napus L. Oilseed crop with high sulfur demand relative to cereals. Nitrogen and sulfur co-management is critical for both yield and oil quality.

Canopy Cover
type: NamedIndividual
type: Growth Response
comment: The fraction of the soil surface obscured by the crop canopy when viewed from above (0–1 or %). Measured by overhead photography or canopy sensors. Relates to light interception and is used in early-season nitrogen status assessment.

Chlorine
type: NamedIndividual
type: Micronutrient
comment: Element Cl. Required for the water-splitting reaction in photosynthesis and for osmotic regulation. Field deficiency is rare because atmospheric deposition and fertilizer impurities usually supply adequate Cl. Wheat responds to Cl on some low-Cl Great Plains soils.

Copper
type: NamedIndividual
type: Micronutrient
comment: Element Cu. Component of plastocyanin (photosynthesis) and several oxidase enzymes. Deficiency is most common on organic soils (histosols) and recently levelled land where subsoil is exposed. Wheat is particularly sensitive.

Corn
type: NamedIndividual
type: Crop Species
comment: Zea mays L. Major row crop with high nitrogen demand (typically 1.0–1.2 kg N per bushel yield goal). Nitrogen management centers on pre-plant and side-dress applications timed to the rapid uptake period (V6–VT).

Falling Number
type: NamedIndividual
type: Wheat Quality Measure
comment: A test measuring alpha-amylase enzyme activity in flour (seconds). Low values (<300 s) indicate excessive starch degradation from pre-harvest sprouting. Not directly nitrogen-responsive but can be influenced by nitrogen-mediated maturity delays that extend exposure to wet conditions.

Farinograph Stability Index
type: NamedIndividual
type: Wheat Quality Measure
comment: The time (minutes) a dough maintains peak consistency during continuous mixing on a Brabender farinograph. Indicates dough tolerance to mechanical processing. Longer stability corresponds to stronger gluten and is associated with higher protein content.

Flour Protein Content
type: NamedIndividual
type: Wheat Quality Measure
comment: Protein concentration of extracted flour (%, 14% moisture basis). Slightly lower than whole-grain protein because bran and germ are removed. The primary determinant of dough strength and bread-making potential.

Flour Yield
type: NamedIndividual
type: Wheat Quality Measure
comment: The percentage of flour extracted from whole grain during milling (typically 68–76% for hard wheat). Influenced by grain hardness, kernel shape, and test weight. Nitrogen management has an indirect effect via kernel size and density.

Gluten Content
type: NamedIndividual
type: Wheat Quality Measure
comment: The mass of wet or dry gluten extracted from flour by washing away starch (%). Gluten is the viscoelastic protein network that gives wheat dough its unique bread-making properties. Directly proportional to flour protein; responsive to nitrogen supply.

Grain Number
type: NamedIndividual
type: Yield Response
comment: The total number of grains per unit area. The yield component with the highest correlation to final yield in most cereals. Determined primarily during the critical period around flowering; nitrogen supply during this window has the greatest impact.

Grain Number Per Spike
type: NamedIndividual
type: Wheat Yield Component
comment: The average number of grains produced per spike, integrating spikelet number and grain set per spikelet. Reflects floret fertility, which is sensitive to nitrogen and environmental stress around anthesis.

Grain Number Per Spikelet
type: NamedIndividual
type: Wheat Yield Component
comment: The average number of grains set within each spikelet. Typically 2–4 in wheat; the basal two florets almost always set grain while distal florets require good nutrition and conditions.

Grain Number Per Tiller
type: NamedIndividual
type: Wheat Yield Component
comment: The average number of grains produced per tiller (including both fertile and infertile tillers in the denominator). A composite measure of tiller fertility and spike productivity.

Grain Protein
type: NamedIndividual
type: Quality Response
comment: The total nitrogen content of whole grain multiplied by a conversion factor (5.7 for wheat, 6.25 for most other crops), expressed as a percentage of dry weight. The single most important quality parameter for hard wheat marketing. Directly responsive to late-season nitrogen supply.

Grain Sorghum
type: NamedIndividual
type: Crop Species
comment: Sorghum bicolor (L.) Moench. Drought-tolerant warm-season cereal. Lower nitrogen demand than corn; susceptible to iron chlorosis on high-pH soils.

Grain Weight
type: NamedIndividual
type: Yield Response
comment: The mass of an individual grain or a defined count of grains (e.g., thousand kernel weight). A fundamental yield component determined during the grain-fill period; sensitive to late-season nitrogen supply and heat stress.

Grain Weight Per Spike
type: NamedIndividual
type: Wheat Yield Component
comment: The total grain mass per individual spike. The product of grain number per spike and individual grain weight; summarises per-spike productivity.

Grain Weight Per Spikelet
type: NamedIndividual
type: Wheat Yield Component
comment: The total grain mass within a single spikelet. A fine-resolution yield component reflecting the combined effect of grain number and grain weight at the spikelet level.

Grain Yield
type: NamedIndividual
type: Yield Response
comment: The mass of harvested grain per unit area, expressed at standard moisture content (e.g., 13.5% for wheat, 15.5% for corn). The primary agronomic response variable for nitrogen management in grain crops. Reported in kg/ha, bu/acre, or t/ha.

Harvest Index
type: NamedIndividual
type: Yield Response
comment: The ratio of grain yield to total aboveground biomass at physiological maturity (dimensionless, typically 0.35–0.55 for modern cereal cultivars). Indicates the efficiency of biomass partitioning to grain. Nitrogen excess can reduce HI by promoting vegetative growth at the expense of grain fill.

Infertile Spike Number
type: NamedIndividual
type: Wheat Yield Component
comment: The count of tillers that produced a spike but set no grain. High infertile spike counts indicate excessive early tillering without adequate resources to sustain all tillers through grain fill — often a symptom of early nitrogen excess followed by late-season stress.

Infertile Tiller Number
type: NamedIndividual
type: Wheat Yield Component
comment: The count of tillers that failed to produce a spike. Some tiller mortality is normal; excessive infertile tillers indicate poor resource allocation or competition within the canopy.

Iron
type: NamedIndividual
type: Micronutrient
comment: Element Fe. Essential for chlorophyll synthesis, electron transport, and enzyme function. Deficiency (iron chlorosis) is common on high-pH calcareous soils where Fe³⁺ is insoluble. Sorghum and soybean are particularly susceptible.

Leaf Area Index
type: NamedIndividual
type: Growth Response
comment: The ratio of total one-sided green leaf area to ground area (dimensionless, m²/m²). LAI drives canopy light interception and is a key determinant of radiation use efficiency. Optimal LAI for wheat is typically 5–7 at flag leaf.

Leaf Number
type: NamedIndividual
type: Growth Response
comment: The count of fully expanded leaves on the main stem (Haun scale in wheat). Used to track phyllochron-based development and schedule growth-stage-dependent management actions.

Loaf Volume
type: NamedIndividual
type: Wheat Quality Measure
comment: The volume of a standard loaf baked from a defined flour weight under controlled conditions (cm³ or mL). The ultimate functional measure of bread-making quality. Strongly correlated with flour protein content and gluten strength.

Magnesium
type: NamedIndividual
type: Secondary Mineral Nutrient
comment: Element Mg. Central atom of the chlorophyll molecule; essential for photosynthesis, enzyme activation, and phosphorus transport within the plant. Deficiency causes interveinal chlorosis on older leaves. Can be supplied by dolomitic lime.

Manganese
type: NamedIndividual
type: Micronutrient
comment: Element Mn. Activates enzymes in photosynthesis (water-splitting complex of Photosystem II) and respiration. Availability decreases sharply above pH 7.5; over-liming is a common cause of Mn deficiency in wheat and soybeans.

Mixing Tolerance
type: NamedIndividual
type: Wheat Quality Measure
comment: The degree to which dough maintains its strength as mixing extends beyond the optimum time (farinograph or mixograph). Good mixing tolerance indicates robust gluten that can withstand industrial processing. Influenced by protein quantity and quality (glutenin-to-gliadin ratio).

Molybdenum
type: NamedIndividual
type: Micronutrient
comment: Element Mo. Essential cofactor for nitrate reductase (nitrogen assimilation) and nitrogenase (biological N fixation in legumes). Required in the smallest quantity of all micronutrients. Deficiency occurs primarily on acid soils; liming usually corrects it.

Nickel
type: NamedIndividual
type: Micronutrient
comment: Element Ni. Required as a cofactor for urease, the enzyme that hydrolyses urea in plant tissues. The most recently confirmed essential element (2004). Deficiency is extremely rare under field conditions.

Nitrate Nitrogen
type: NamedIndividual
type: Nutrient Form
is form of: Nitrogen
comment: NO₃⁻-N. The oxidised, anionic form of soil mineral nitrogen. Highly mobile in soil solution; moves freely with percolating water, making it the primary form subject to leaching losses. Also the substrate for denitrification under anaerobic conditions. The dominant N form taken up by most dryland crops.

Nitrogen
type: NamedIndividual
type: Primary Mineral Nutrient
comment: Element N. The nutrient most commonly limiting crop yield in non-leguminous systems. Required for amino acid, protein, chlorophyll, and nucleic acid synthesis. Highly mobile in both soil and plant; subject to multiple loss pathways (leaching, denitrification, volatilisation). Typical sufficiency range in wheat tissue: 2.0–3.5% N at flag leaf stage.

Number of Spikelets
type: NamedIndividual
type: Wheat Yield Component
comment: The count of spikelets per spike. Determined during spikelet initiation (double-ridge stage through terminal spikelet); sets the maximum number of grain sites per spike.

Number of Spikes
type: NamedIndividual
type: Wheat Yield Component
comment: The count of fertile (grain-bearing) spikes per unit area. The primary tiller-derived yield component; strongly influenced by early-season nitrogen supply and plant population density.

Partial Factor Productivity
type: NamedIndividual
type: Nutrient Use Efficiency
comment: PFP = Yield_fertilised / N_applied. Expressed in kg grain per kg N applied. The simplest NUE metric — it does not require an unfertilised control. Useful for benchmarking nitrogen productivity across farms and regions but confounds soil N supply with fertilizer N contribution.

Phosphorus
type: NamedIndividual
type: Primary Mineral Nutrient
comment: Element P. Essential for energy transfer (ATP/ADP), root development, and reproductive growth. Relatively immobile in soil; availability is strongly pH-dependent (optimal 6.0–7.0). Managed on a build-and-maintain basis using soil-test phosphorus as the primary decision criterion.

Physiological Efficiency
type: NamedIndividual
type: Nutrient Use Efficiency
comment: PE = (Yield_fertilised − Yield_unfertilised) / (N_uptake_fertilised − N_uptake_unfertilised). Expressed in kg grain per kg N absorbed. Measures how efficiently the plant converts absorbed nitrogen into grain. Primarily a genetic trait influenced by cultivar and environmental interactions.

Plant Height
type: NamedIndividual
type: Growth Response
comment: The vertical distance from the soil surface to the top of the canopy (excluding awns), measured in cm. Influenced by nitrogen supply, growth regulators, and cultivar genetics. Excessive height increases lodging risk.

Potassium
type: NamedIndividual
type: Primary Mineral Nutrient
comment: Element K. Regulates stomatal function, osmotic balance, enzyme activation, and disease resistance. Absorbed as K⁺; does not form organic compounds in the plant but is highly mobile within tissues. Deficiency symptoms appear first on older leaves.

Recovery Efficiency
type: NamedIndividual
type: Nutrient Use Efficiency
comment: RE = (N_uptake_fertilised − N_uptake_unfertilised) / N_applied. Expressed as a fraction (0–1) or percentage. Measures the proportion of applied nitrogen that was absorbed by the crop. Typical values for cereal systems: 0.40–0.60. The most direct indicator of fertilizer use versus loss.

Root Length
type: NamedIndividual
type: Growth Response
comment: The total or maximum length of roots, measured in cm or km/m³ of soil. Root length density determines the volume of soil explored for water and nutrients. Nitrogen placement and soil physical conditions both influence root proliferation.

Soybean
type: NamedIndividual
type: Crop Species
comment: Glycine max (L.) Merr. Legume with symbiotic nitrogen fixation; typically does not receive nitrogen fertilizer. Phosphorus and potassium management are the primary nutrient concerns.

Spike Dry Weight
type: NamedIndividual
type: Wheat Yield Component
comment: The total dry mass of the spike including the rachis, glumes, and grains. Used to calculate spike harvest index (grain weight / spike dry weight), which indicates partitioning efficiency within the spike.

Spike Sterility Index
type: NamedIndividual
type: Wheat Yield Component
comment: The proportion of potential grain sites within a spike that failed to set grain (dimensionless, 0–1). High sterility indicates stress during the critical period around anthesis.

Sulfate Sulfur
type: NamedIndividual
type: Nutrient Form
is form of: Sulfur
comment: SO₄²⁻-S. The plant-available anionic form of soil sulfur. Like nitrate, sulfate is mobile in soil solution and subject to leaching in high-rainfall or irrigated environments. Measured by soil testing to assess S availability for sulfur-responsive crops.

Sulfur
type: NamedIndividual
type: Secondary Mineral Nutrient
comment: Element S. Required for synthesis of the amino acids cysteine and methionine, and hence for protein quality. Increasingly deficient in agricultural soils since the reduction of atmospheric SO₂ deposition. Critical for canola, alfalfa, and high-protein wheat.

Test Weight
type: NamedIndividual
type: Quality Response
comment: The mass of grain per unit volume (kg/hL or lb/bu). Indicates grain density and soundness. A statutory grading factor for wheat, corn, and sorghum. Nitrogen excess can reduce test weight by delaying maturity and promoting small, shrivelled grains during heat stress.

Thousand Kernel Weight
type: NamedIndividual
type: Quality Response
comment: The mass of 1000 individual grains (g). An alternative expression of grain size that is both a yield component and a quality indicator. Grain size affects milling yield and is influenced by nitrogen supply during grain fill.

Tiller Number
type: NamedIndividual
type: Growth Response
comment: The count of tillers per unit area or per plant at a specified growth stage. Early-season nitrogen strongly promotes tillering in cereals; however, late tillers often fail to produce grain.

Winter Wheat
type: NamedIndividual
type: Crop Species
comment: Triticum aestivum L. (winter type). The dominant dryland crop in the Great Plains. Nitrogen management for winter wheat is the primary focus of this ontology. Key response variables include grain yield, test weight, grain protein, and milling quality.

Zinc
type: NamedIndividual
type: Micronutrient
comment: Element Zn. Required for auxin synthesis, carbonic anhydrase activity, and protein synthesis. Deficiency causes stunted internodes and small leaves. Common on high-pH, low-organic-matter soils; corn and sorghum are highly responsive.

Early
type: NamedIndividual
type: Maturity Group
comment: Reaches anthesis and maturity earlier than the regional average. Balances escape from late-season stress with reasonable yield potential.

Late
type: NamedIndividual
type: Maturity Group
comment: The latest maturing group. Extended vegetative growth and grain fill. Highest yield potential under cool, wet seasons but highest risk of heat stress and terminal drought in the Great Plains.

Medium
type: NamedIndividual
type: Maturity Group
comment: The benchmark maturity class for the region. Reaches anthesis and maturity at the time considered optimal for the local climate. Most commercial varieties fall in this range.

Medium Early
type: NamedIndividual
type: Maturity Group
comment: Slightly earlier than medium maturity. A common classification for varieties that provide moderate stress avoidance with good yield potential.

Medium Late
type: NamedIndividual
type: Maturity Group
comment: Slightly later than medium maturity. Longer vegetative phase may increase yield potential under favourable conditions but increases exposure to late-season heat and disease.

0/100/0 (All Spring)
type: NamedIndividual
type: Nitrogen Timing Split
comment: 100% of nitrogen applied in spring. Eliminates fall-to-spring loss risk but may limit early tillering in nitrogen-deficient soils. Requires soil nitrate or organic matter to carry the crop through fall and winter.

100/0/0 (All Fall)
type: NamedIndividual
type: Nitrogen Timing Split
comment: 100% of nitrogen applied in fall (pre-plant or at sowing). Simple logistics but maximum exposure to early-season leaching and denitrification losses.

40/40/20 (Fall + Spring + Anthesis)
type: NamedIndividual
type: Nitrogen Timing Split
comment: 40% fall, 40% spring, 20% at anthesis (flag leaf to flowering). Three-way split targets late-season protein accumulation while maintaining yield. Most complex logistics but best potential for both yield and protein optimization.

40/60/0 (Fall + Spring)
type: NamedIndividual
type: Nitrogen Timing Split
comment: 40% applied in fall, 60% applied in spring (topdress at greenup to jointing). The most common split in Kansas winter wheat production. Reduces early-season loss risk while providing adequate fall nutrition for tillering.

Super Early
type: NamedIndividual
type: Maturity Group
comment: The earliest maturing group. Reaches anthesis and maturity significantly earlier than the regional average. Useful for avoiding late-season heat stress but may have reduced yield potential due to shorter grain fill duration.

Alcaligenes
type: NamedIndividual
type: Denitrifying Organism
comment: A genus of Gram-negative, obligately aerobic bacteria with some species (A. faecalis) capable of denitrification under micro-aerophilic conditions. Common in soil and aquatic environments; contributes to denitrification in the transition zone between aerobic and anaerobic soil microsites.

Bacillus
type: NamedIndividual
type: Denitrifying Organism
comment: A genus of Gram-positive, spore-forming bacteria. Several species (B. licheniformis, B. subtilis) are capable of denitrification under anaerobic conditions. Their spore-forming ability allows survival through adverse conditions, enabling rapid resumption of denitrification when soils become waterlogged after dry periods.

Paracoccus denitrificans
type: NamedIndividual
type: Denitrifying Organism
comment: A Gram-negative, facultatively anaerobic bacterium and one of the best-characterised model organisms for denitrification research. Possesses all four reductases of the complete denitrification pathway (NO₃⁻ → NO₂⁻ → NO → N₂O → N₂). Formerly classified as Micrococcus denitrificans.

Pseudomonas
type: NamedIndividual
type: Denitrifying Organism
comment: A genus of Gram-negative, rod-shaped, facultatively anaerobic bacteria. Contains several prominent denitrifying species (P. aeruginosa, P. stutzeri, P. fluorescens). The most widely studied and agronomically important group of soil denitrifiers, active across a broad range of soil conditions.

Thiobacillus denitrificans
type: NamedIndividual
type: Denitrifying Organism
comment: A chemolithoautotrophic bacterium unique in coupling sulfur oxidation to denitrification: it uses NO₃⁻ as the terminal electron acceptor while oxidising reduced sulfur compounds. Relevant in waterlogged soils with high sulfide content. Not to be confused with Thiobacillus thioparus, which is a sulfur oxidiser but not a denitrifier.