Decision support tree for nutrient management following cover crops (desk study)

Cover crops provide a wide range of benefits, such as the reduction of soil erosion and nitrate-leaching risks.

However, there are several big knowledge gaps, especially related to legacy effects, including the amount and timing of nitrogen (N) release from cover crop residues.

This gap is complicated by:

• The wide range of cover crop species mixes
• The diversity of UK agroclimatic conditions (e.g. soil types, cropping and weather)
• The various management practices used (e.g. sowing/destruction dates and methods)

The lack of robust evidence, especially in UK production systems, means that the 2026 edition of the AHDB Nutrient Management Guide (RB209) provides limited information about the impact of cover crops on soil nitrogen supply (SNS).

It also has no guidance on the release of other major nutrients to cash crops, such as phosphorus (P), or how management (e.g. termination approach) impacts nutrient release.

The lack of specific data on cover crop nutrients means many farmers do not account for them when managing following cash crops.

2025 desk study

A 2025 desk study reviewed research on nutrient uptake and release from cover crops in temperate regions and identified the potential to improve guidance.

In many studies, cover crops supplied up to 30 kg/ha of nitrogen to the following crop, with 31 to 60 kg/ha also commonly observed.

The research only identified limited information on nutrient-release timing. The UK-based studies found most nutrients are released almost immediately (within several days).

A survey of farmers and advisors (150 respondents) was also conducted. This found that most respondents (86%) were greatly interested in having a decision support tool that can account for nutrients taken up by and released from cover crops.

The research reviewed the evidence and methodologies for estimating and predicting the timing and amount of nutrients released from cover crops and provided a roadmap of potential options to support decision making.

One option included a decision support tree, which will be developed in this follow-up desk study.

The work continues to receive co-funding from three water companies: Anglian Water, Southern Water and Wessex Water.

2026 desk study

The 2026 desk study builds on findings to date and has four work packages:

1. Identify and review robust data on cover crop nutrient uptake and release

Collate robust data to underpin the development of a decision support tree, including the use of anonymised information from industry sources.

2. Develop an initial decision support tree

Develop an initial simple, practical and robust decision support tree, which indicates confidence levels and has scope for further development.

It will consider many factors, including:

• Soil type
• Conditions
• Cover crop species
• Planting dates
• Cover crop establishment/growth
• Destruction method and timing
• Previous and following crop
• Similar organic materials (such as companion crops)
• Nutrient release

The work will also consider practical measures and assessments (e.g. of the crop and soil) that will inform the decision-making process.

3. Co-design the final decision support tree

Work with end-users to co-design the final decision support tree to make sure it meets the needs of farmers and advisors in critical formats (e.g. for web pages and publications).

4. Produce a final report

Provide a complete record of the work and include recommendations on further research to improve nutrient management guidance.

Added-value activities

The researchers will also conduct activities that add value to the research requirement outlined in the original AHDB research call.

This element will build on initial activity in the 2025 desk study that examined models that account for nutrient uptake and release from cover crops.

Model examples include:

• The MERCI nitrogen model (France)
• NDICEA nitrogen and carbon planner (The Netherlands)

Specifically, the research will focus on the MERCI model to validate the decision support tree, indicate how relevant the model is for UK situations and identify knowledge gaps.

Most of the added-value work will be conducted in the final month of the project.

Supporting stakeholders

The added value element is funded by Anglian Water, Southern Water and Wessex Water (approximately £5,000 each).

It also includes £2,200 in-kind for the provision of two BBRO trial sites to ground-truth the decision-making tools assessed during the desk study (this aspect will finish after this desk study ends).

These costs have been included in the ‘Total project value’ (shown at the top of the page).

The project has also received additional in-kind contributions for the provision of cover crop expertise and resources to develop the decision support tree for use in arable rotations and the examination of models.

• British Beet Research Organisation (BBRO): Providing specialist expertise in sugar beet agronomy and trial data (including cover crop data)
• The Maize Growers Association: Providing specialist expertise in maize agronomy
• Processors and Growers Research Organisation (PGRO): Providing specialist expertise in pea and bean agronomy and trial data on cover crops in vining pea rotations
• Frontier: Providing specialist expertise in cover crops and nutrition and cover crop trial data

Providing answers to your questions

This research project was funded via a levy-payer-led commissioning process.