How to evaluate cover crops on-farm

1. Research and identify your objectives

Before starting, think about your key objective(s), which could cover:

• Managing fertility, such as adding or preventing the loss of nitrogen
• Incorporating large amounts of organic residue
• Developing a surface mulch
• Controlling erosion
• Dealing with acidic soils
• Alleviating compaction
• Tackling weeds, diseases or pests

Additionally, consider if the cover crop could make some things worse (e.g. clubroot disease) and if it fits in with the rotational requirement, soil type and equipment.

Identify the best information sources to inform and guide your decisions.

Always observe what other farmers are doing.

Create a plan or schedule:

• What will happen when, such as establishment and destruction
• What you expect (hope) the cover crop will look like (at various stages)
• Equipment, input or support requirements
• How you aim to assess the impact
• What the estimated budget is

2. Test a few options (including controls)

Be prepared to test several options that appear suited to your objectives.

• Establish field strips of your chosen cover crops (typically, tramline-width strips down the field)
• Include a control strip, such as a fallow without a cover crop or a ‘farm-standard’ treatment (such as a typical autumn cultivation)
• If only one cover crop option is being evaluated, consider a simple field split
• Aim to arrange strips or splits so that known soil variation goes across (rather than with) the splits
• Ideally, replicate strips within fields and across different fields or sequential seasons to provide information on variability

Consider evaluating other aspects of cover cropping, such as seed rates, destruction approach or in-season management.

However, do not chase too many objectives at the same time.

3. Monitor progress and responses

Monitoring trials is essential, but it does not need to be complicated.

• Keep records over the season
• Photographs are quick and effective
• Aim to do some simple assessments linked to the objective(s) – for example, assess soil structure with a VESS test
• Capture the yield response in following crop(s) from cover crop and control treatments

If using a yield-mapping combine, ensure it is calibrated and set up with appropriate values.

If yield mapping is not available, use records from a combine yield meter or weighbridge.

Keep the set-up the same during the harvest of all trial areas.

Make comparisons as fair as possible.

Ideally, keep the header completely ‘in work’ with a constant harvested width and, ideally, the same combine direction.

Take consistent readings, such as in the middle of an area or at known set points (and take a mean).

Note yields on a field-trial map.

Not all yield responses occur in the cash crop immediately following the cover crop. Some occur in subsequent crops (or even after more than one cycle of cover crop use).

Therefore, monitor yield one and two years following the cover crop (at least).

4. Evaluate the response

Although the economic cost and return (cash-crop yield) is important, it may not be as important as achieving the objective set (which may be hard to cost).

Economic assessments should be based on treatment costs (including seed, establishment, management and destruction) and yield responses over (at least) the following two cash crops.

Additional payments*, residual nutrient benefits (e.g. phosphate index raised) and indirect value (e.g. management of soil erosion) should also be considered.

*There are cover crop options in the Countryside Stewardship schemes and Sustainable Farming Incentive.

5. Think about next steps

You are unlikely to get everything right the first time.

Consider the evaluation.

Be prepared to modify and develop the approach and go again.