Cover crops: Pros, cons and agronomic considerations uncovered by review

Growers can access the scientific theory behind cover crops, thanks to the results of a comprehensive review funded by AHDB Cereals & Oilseeds.

The nine-month review, by ADAS and NIAB TAG, provides the most comprehensive analysis of cover crops to date and acts as a practical reference source to aid with cover crop species selection and management.

Ensuring cover crops are established early – with a clear objective(s) in mind – and considering benefits over an appropriate timeframe are among the review’s key recommendations.

Clear objectives

Four broad objectives for cover crops were identified by the review: to improve soil fertility; to benefit soil structure; to tackle weeds and pests; and to manage the environment – including meeting Ecological Focus Area requirements under the Basic Payment Scheme.

Charlotte White, ADAS and lead author, said: “Test a couple of cover crop options and compare them against your standard cropping practice to find out which option meets your objective best.

When assessing a cover crop’s direct financial benefit, the review found that benefits should be measured beyond the next cash crop.

Dr White continued: “Conducting a long-term cost-benefit analysis is not easy, but the practical guidance in the review will help growers make relatively robust assessments of a cover crop’s potential value to find the one that fits their system best.”

Agronomic considerations

The scientific basis of reported cover crop functions and cover crop agronomy was also reviewed, including cover crop choices, establishment methods, starter fertiliser requirements, pest management and cover crop destruction.

In terms of agronomy, getting cover crops established in the late summer to early autumn period was considered to be the most important key to success.

Analysis of nitrogen (N) uptake information revealed that cover crops typically take up 30 to 100kg N/ha, with 10 to 100kg N/ha released in the following crop. Nitrogen fixation was also determined to be most effective between 7°C and 20°C. Organic matter increases following a cover crop were also determined, which ranged from 0 to 42 per cent.

It was also recommended that a target canopy cover of at least 30 per cent is required for the purpose of reducing soil erosion risks.

The review, which includes information on how to evaluate cover crops, case studies and recommendations for further research, can be found at cereals.ahdb.org.uk/covered

The web page also includes video footage of the review co-author, Ron Stobart NIAB TAG, talking on cover crop ‘pros and cons’ at the 2016 AHDB Agronomists’ Conference.