Fertilizer pollution measures the application rates of agricultural fertilizers -- Nitrogen (N), Phosphorus (P), and Potassium (K) -- and estimates the fraction that escapes the agricultural system and becomes environmental pollution. The indicator provides quantitative information on the impact of intensive agriculture on three interconnected phenomena: eutrophication of surface water bodies, groundwater contamination from nitrate leaching, and greenhouse gas emissions (N2O) from denitrification and nitrogen volatilisation.
Nitrogen has the most severe environmental consequences: up to 50% of applied nitrogen can disperse into the environment through leaching, volatilisation as ammonia (NH3), and denitrification into nitrous oxide (N2O), a greenhouse gas with 265 times the warming potential of CO2 (Galloway et al., 2008). Phosphorus, while less mobile, is the primary driver of eutrophication in lakes and slow-moving water bodies. Potassium excess contributes to soil salinisation and structural degradation.
The platform presents this KPI through a gauge with a nutrient selector (N, P, K), a site-versus-control comparison chart, and three separate map layers -- one per nutrient element.
The KPI uses the NPKGRIDS dataset (Global Fertilizer Application Rates) from the University of Minnesota / Global Landscapes Initiative (Ludemann et al., 2022), at 10 km resolution. The dataset provides separate application rates for 175 crop classes aggregated globally for the reference year 2020:
Loss fractions are applied to estimate the portion of each nutrient that becomes environmental pollution:
| Nutrient | Loss Fraction | Main Mechanisms |
|---|---|---|
| Nitrogen (N) | 50% | Nitrate leaching, NH3 volatilisation, N2O denitrification |
| Phosphorus (P) | 15% | Surface erosion, agricultural runoff |
| Potassium (K) | 30% | Leaching, deep percolation |
Formula: Pollution N = Total Application Rate N x 0.50
Formula: Pollution P = Total Application Rate P x 0.15
Formula: Pollution K = Total Application Rate K x 0.30
The calculation produces three separate layers, each representing the estimated quantity of nutrient dispersed into the environment (in kg/ha/year) within and around the study polygon. The raster data is upscaled via bilinear interpolation (factor 6, from ~10 km to ~1.67 km) and visualised with a green-to-red colourmap with gamma correction (gamma = 0.4) to emphasise high-pollution areas.
| Source | Provider | Coverage | Resolution | Period |
|---|---|---|---|---|
| NPKGRIDS v4 -- Global Fertilizer Application Rates (WRD_NPKGR_20) | University of Minnesota / Global Landscapes Initiative | Global | 10 km | 2020 |
Gauge. A semicircular arc chart (CaRoiChart) displaying the site's fertilizer pollution level for the selected nutrient, with a comparison to the control area.
Purpose: To show at a glance how much fertilizer-derived pollution affects the site for a given nutrient (Nitrogen, Phosphorus, or Potassium), and how it compares to the surrounding control area.
Description: The card header shows the sub-topic badge "Pollution" and an info tooltip icon. Below the header, a dropdown selector allows the user to choose the nutrient element: Nitrogen (N), Phosphorus (P), or Potassium (K). The gauge arc is divided into five coloured segments from green (low pollution) to red (high pollution), with separate needles for the site (ROI) and the control area (CA). The current pollution value in kg/ha is displayed numerically.
How it's calculated: The value shown is the mean estimated pollution for the selected nutrient within the site polygon. It is computed by summing the application rates of 175 crop classes from the NPKGRIDS dataset, then multiplying by the loss fraction (N: 50%, P: 15%, K: 30%). The control area value is calculated the same way for the surrounding reference polygon.
Note: This indicator is inverted -- lower values indicate better conditions.
Legend: The quality scale differs per nutrient element. Below are the ranges for Nitrogen (the most impactful):
| Level | Range (kg/ha) -- Nitrogen | Color | Meaning |
|---|---|---|---|
| A | 0 -- 100 | ■ #00A67A | Minimal impact; sustainable agricultural practices or natural areas |
| B | 100 -- 300 | ■ #00DF80 | Low-moderate impact; agriculture with room for improvement |
| C | 300 -- 700 | ■ #FFD21E | Significant pressure; ecosystems under stress |
| D | 700 -- 1,500 | ■ #FF8B16 | High nitrogen load; aquatic habitats severely at risk |
| E | > 1,500 | ■ #FF367F | Extreme nitrogen pollution; severe eutrophication and N2O risk |
Interpretation example:
If the gauge shows 450 kg/ha for Nitrogen (grade C, yellow), it means the estimated nitrogen pollution from fertilizers is moderate -- the site is under significant agricultural pressure, with a meaningful portion of applied nitrogen escaping into the environment through leaching and volatilisation. Switching to Phosphorus might show 85 kg/ha (grade C), indicating moderate phosphorus runoff risk contributing to eutrophication of nearby water bodies.
Bubble Chart. A site-versus-control comparison chart showing the fertilizer pollution level for both the monitored site (ROI) and the surrounding control area (CA).
Purpose: To allow the user to compare the site's fertilizer pollution against the broader landscape and determine whether the site is more or less affected by agricultural nutrient inputs than its surroundings.
Description: The chart displays paired values for the site and the control area under the selected nutrient element. The selected nutrient is controlled by the dropdown on the gauge card above. The description reads "Site-control fertilizer pollution comparison".
How it's calculated: Each value represents the mean estimated pollution for the respective polygon (site or control) for the selected nutrient. Both use the same NPKGRIDS data, loss fractions, and bilinear interpolation methodology.
Note: This indicator is inverted -- lower values indicate better conditions.
Interpretation example:
If the site shows 450 kg/ha and the control area shows 520 kg/ha for Nitrogen, the monitored site has slightly lower nitrogen pollution than its surroundings -- a relatively positive signal, though both areas are under significant fertilizer pressure (grade C).
Map Layer. An interactive map overlay showing the spatial distribution of estimated nitrogen fertilizer pollution, derived from the NPKGRIDS dataset.
Purpose: To provide a spatially resolved view of nitrogen pollution from fertilizer application across the site and surrounding area, identifying agricultural intensity hotspots.
Description: When the "Nitrogen (N)" layer chip is selected under the Pollution category in the map panel, the nitrogen pollution raster is displayed over the base map. The legend panel shows the nutrient name and a continuous colour gradient bar from green (low pollution) to red (high pollution). An opacity slider and download button are available.
How it's calculated: The raster is produced by summing nitrogen application rates across all 175 crop classes from the NPKGRIDS dataset, applying the 50% loss fraction, upscaling via bilinear interpolation, and rendering with a green-to-red colourmap (gamma = 0.4).
Note: This indicator is inverted -- lower values indicate better conditions.
Legend: Continuous green-to-red colour gradient with gamma correction (gamma = 0.4). The scale compresses low-pollution areas and emphasises high-pollution hotspots. Range: 0 to approximately 9,720 kg/ha (raw application rate before loss fraction).
Interpretation example:
If the map shows intense red over a broad agricultural plain and green over an adjacent mountainous area, the spatial contrast reveals the localised impact of intensive crop farming on nitrogen pollution -- areas with high fertilizer application rates are clearly distinguishable from natural or low-intensity zones.
Map Layer. An interactive map overlay showing the spatial distribution of estimated phosphorus fertilizer pollution, derived from the NPKGRIDS dataset.
Purpose: To visualise phosphorus pollution patterns across the site and surrounding area, identifying zones with high eutrophication risk for nearby water bodies.
Description: When the "Phosphorus (P)" layer chip is selected under the Pollution category in the map panel, the phosphorus pollution raster is displayed over the base map. The legend panel shows the nutrient name and a continuous colour gradient bar.
How it's calculated: The raster is produced by summing phosphorus application rates across all 175 crop classes from the NPKGRIDS dataset, applying the 15% loss fraction, upscaling via bilinear interpolation, and rendering with a green-to-red colourmap (gamma = 0.4).
Note: This indicator is inverted -- lower values indicate better conditions.
Legend: Continuous green-to-red colour gradient with gamma correction (gamma = 0.4). Range: 0 to approximately 1,598 kg/ha (raw application rate before loss fraction).
Interpretation example:
If the map shows orange-red tones over irrigated rice paddies and green over surrounding grassland, the phosphorus pollution pattern highlights the higher fertilizer demand of intensive rice cultivation, which produces greater phosphorus runoff risk into drainage channels and waterways.
Map Layer. An interactive map overlay showing the spatial distribution of estimated potassium fertilizer pollution, derived from the NPKGRIDS dataset.
Purpose: To visualise potassium pollution patterns across the site and surrounding area, identifying zones where excess potassium may contribute to soil salinisation and water contamination.
Description: When the "Potassium (K)" layer chip is selected under the Pollution category in the map panel, the potassium pollution raster is displayed over the base map. The legend panel shows the nutrient name and a continuous colour gradient bar.
How it's calculated: The raster is produced by summing potassium application rates across all 175 crop classes from the NPKGRIDS dataset, applying the 30% loss fraction, upscaling via bilinear interpolation, and rendering with a green-to-red colourmap (gamma = 0.4).
Note: This indicator is inverted -- lower values indicate better conditions.
Legend: Continuous green-to-red colour gradient with gamma correction (gamma = 0.4). Range: 0 to approximately 3,266 kg/ha (raw application rate before loss fraction).
Interpretation example:
If the map shows mostly yellow-green across the study area with isolated red patches near fruit orchards, the potassium pollution pattern reveals that orchards receive higher potassium fertilisation than surrounding crops, creating localised excess that can leach into deeper soil layers.
Highlights Table Row. A row in the multi-KPI comparison highlights table showing the fertilizer pollution level for the selected site and its control area.
Purpose: To allow quick comparison of fertilizer pollution across sites in a single summary view.
Description: A labelled row showing the pollution value for the site (ROI) and the control area (CA), colour-coded by quality grade (A--E). The row label reads "Fertilizer Pollution".
How it's calculated: Same computation as the gauge element. The displayed value is the mean pollution for the primary nutrient (Nitrogen) mapped to the A--E quality scale.
Note: This indicator is inverted -- lower values indicate better conditions.
Interpretation example:
If the site shows grade D (orange) and the control area shows grade C (yellow) for nitrogen, the site has higher fertilizer pollution than its surroundings -- an indication of more intensive agricultural activity within the monitored area.
Assessment Sidebar Row. A grade row in the Pollution section of the assessment sidebar, showing the fertilizer pollution grade for the site.
Purpose: To provide a quick letter-grade summary of fertilizer pollution within the broader environmental risk assessment.
Description: A single row labelled "Fertilizer Pollution" with a coloured grade badge (A--E). Grade A (green) indicates minimal fertilizer pollution; grade E (pink-red) indicates extreme pollution levels.
How it's calculated: The letter grade is derived from the mean nitrogen pollution value mapped to the A--E scale: A = 0--100 kg/ha, B = 100--300 kg/ha, C = 300--700 kg/ha, D = 700--1,500 kg/ha, E = > 1,500 kg/ha.
Note: This indicator is inverted -- lower values indicate better conditions.
Interpretation example:
A grade B means the site's nitrogen fertilizer pollution is between 100 and 300 kg/ha -- a low-to-moderate level, suggesting agricultural activity with manageable environmental impact. Improving to grade A would require either reduced fertilizer application or adoption of precision agriculture techniques.
See the Calculation Methodology section for the core computation. Additional processing details are documented here for expert users.