Nutrient release from cover crops (desk study)

Co-funded by Anglian Water, Southern Water, Wessex Water and AHDB, this desk-based project explored the potential to develop a decision support tool (DST) for the UK that accounts for nutrient release from cover crops and similar organic materials (such as companion crops).

The project was split into five tasks.

Task 1: Quick scoping review on the evidence and methodologies for estimating and predicting the timing and amount of nutrients released from cover crops

Fifty-one studies were identified (12 from the UK) from both peer-reviewed and grey literature. These studies yielded 549 nutrient release measurements, 453 of which were from field experiments. Most measurements were from the UK (165), closely followed by Germany and Denmark.

Many studies found that cover crops supplied up to 30 kg/ha of nitrogen to the following crop. However, 31–60 kg/ha was also commonly observed. A small number of studies recorded greater contributions (over 61 kg/ha). In the UK studies, rye and mustard species were frequently associated with the 31–60 kg/ha nitrogen category.

On nutrient-release timing, there were fewer studies, with most suggesting a relatively quick release of nutrients following cover crop destruction. UK-based studies found most nutrients are released almost immediately (within seven days).

Task 2 and 3: Quick scoping review and evaluation of the cover crop decision support tools available internationally

Seven potential tools were identified, three of which predicted nutrient supply from cover crops. These three tools – MERCI, CC-NCALC and the Organic Fertilizer and Cover Crop Calculator (OFCC) – were shortlisted for an in-depth review of all available supporting literature, test runs (where appropriate) and, in the case of MERCI and CC-NCALC, an interview with the tools’ providers. A SWOT (strengths, weaknesses, opportunities and threats) analysis was performed on the findings, focusing on their potential for use as a cover crop DST in the UK.

The MERCI model was identified as the most suitable tool for UK adaptation as it was most reflective of UK practice, with more similar crops, soils and climate (particularly rainfall). It has greater functionality (e.g. predicts P, K, Mg and S supply and allows for grazing of cover crops) and potential accuracy (e.g. accounts for leaching post-destruction), and it does not require laboratory test results to complete calculations.

Task 4: The practicality of a potential cover crop DST for farmers and other end users and the likely benefits compared to current practice

A survey of 151 farmers and advisers interested in, or currently growing and/or advising on, cover crops showed a high interest in a decision support tool.

In total, 43% of respondents take account of nutrient supply when producing a nutrient management plan for the following crop, while the remaining 57% do not. Nitrogen, rather than phosphate or potash supply, from cover crops was most frequently accounted for.

The majority (86%) of respondents indicated that, if available, they would use a DST that will help guide nutrient management planning following cover cropping. When asked to select their top three features, these included:

1. Providing the fertiliser replacement value
2. Information on the type and amount of nutrient released
3. The impact of destruction timing and method on nutrient release

Task 5: Recommendations for the future route to developing a decision support system

Five recommendations were made alongside roadmaps to develop a decision support tool that will support UK farmers with nutrient management planning decisions following cover crops. These were:

1. Update general guidance in the Nutrient Management Guide (RB209)
2. Update general guidance on the Cover Crop Guide website with outputs of the project
3. Develop a decision support tree that could be integrated into options 1 and 2
4. Work with the MERCI model team to develop a UK version of the tool
5. Develop a cover crop protocol to capture evidence on cover crop performance in a consistent way (could link to option 2, 3 or 4)

While the fifth recommendation (“Develop a cover crop protocol…”) is not strictly a DST, it was included due to the benefits of supporting farmers on how best to measure nutrient uptake following cover crops and the potential for a standard protocol to provide new evidence which could then support future development of recommendations 2, 3 and 4.

A review of the five different recommendations provided no clear outcome for the single best option to implement, with each option having benefits and considerations.

Overview of results

Watch a presentation about this research (Agronomy Conference 2025)

Providing answers to your questions

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