Research and analysis

The nitrate leaching tool: summary

Published 10 May 2021

The Environment Agency has developed a tool to estimate annual losses of nitrate (N) at the field and farm scale using data provided by farmers during farm visits. The tool will help the Environment Agency and farmers to identify more sustainable farming practices that prevent environmental pollution.

1. Background

Few of the nutrient management tools currently available estimate N losses to the environment at the field scale. Farmers are therefore often unaware of the potential risks of their land management actions.

The Nitrate Leaching Tool (NLT) models N losses that could occur as a direct result of individual farm practices and evaluates a range of leaching measures that farmers can put in place. The NLT helps farmers, their advisors, environmental regulators and water companies to discuss these issues and promotes a collaborative approach for identifying solutions.

2. Development

The tool has been piloted in collaboration with water companies and independent agricultural advisers. The project involved liaison with over 60 farmers across variable farming practices, from high input arable farming to lower input rough grazing. It has also been applied across many soil types and the major chalk, limestone and sandstone aquifers of the UK.

3. Approach

The NLT is a spreadsheet based tool designed to be easy to use. The tool uses information about local soils and climate together with land use and management information provided by the farmer. The calculations and principles are widely accepted, being based on peer reviewed papers and applied in several industry tools. The technical reference manual provide full details for transparency.

Predictions of N loss calculated by the NLT have been benchmarked against the industry model Farmscoper and verified against field measurements. Field data was provided by Wessex Water for 250 fields in South West England based on porous pot samples, taken regularly during the autumn months over a time period of 8 winters (2006-2014).

4. Results

A summary of the main findings is provided below. The full details can be found in the user guide appendices:

• NLT simulations of low risk fields like forage maize generally show good agreement with field data.
• High risk fields such as winter oil seed rape are identified as higher risk by the NLT, although agreement with field measurements is often less good.
• Predictions from the NLT and Farmscoper are similar for a range of “reasonable” fertiliser applications. However, the NLT may overestimate the leached N for extreme application scenarios.
• Application of Farmscoper and the NLT to model N losses from the Newbald Becksies catchment found that the highest risk fields were consistently identified by both models. Farmscoper predictions of leached N concentrations were lower than observed, whist NLT predictions were higher.

5. Conclusions

Extensive testing of the NLT has increased the range of land use and management activities captured by the tool. The findings highlight some considerations that users of the tool should be aware of. In particular, the NLT should be used with nutrient planning or yield optimising tools to estimate the nitrogen losses that may result from a proposed nutrient plan.

The NLT complements existing tools available to predict N leaching at larger scales. These are often used for targeting resources and advice at the national or catchment scale. The farm and field scale of the NLT makes it particularly useful for engaging with farmers in high risk areas to identify N reduction actions tailored to each individual’s situation.

6. Further information

This summary relates to information from project [project number], reported in detail in the following output(s):

• Report: SC160010
• Title: The Nitrate Leaching Tool – technical reference
• Title: The Nitrate Leaching Tool – user guide
• Project managers: Natalie Kieboom, Chief Scientist’s Group and Giles Bryan, Wessex groundwater & contaminated land team
• Research Contractor: Wood Environment & Infrastructure Solutions. Shinfield Park, Reading RG2 9FW. Tel: 0118 913 1234

This project was co-funded by the Environment Agency’s Wessex Groundwater & Contaminated Land team and the Chief Scientist’s Group. The Chief Scientist’s Group provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk

© Environment Agency