Cover crops – is it worth it?

Written by: Mandy Stoker

My farmer’s survey reveals the current state of play and provides an insight into views of this increasingly popular options for soil preservation.

Agriculture is undergoing a green revolution.  Priorities are shifting away from greater yields at any cost, and towards a more compassionate system that invests in the environment and provision of nutritious food.  Methods that enrich agricultural land, including the use of cover crops, are being taken more seriously but is the roll out fast enough to make the serious changes needed to achieve those goals?

A total of 2395 farmers responded to the 2014/15 DEFRA survey on the land they managed voluntarily under the Campaign for the Farmed Environment.  In this survey, cover crops included winter cover crops, brassica fodder crop and over winter stubble. The last recorded data in 2014/15 showed a total of 99,305 hectares (ha) under cover crops however, this was a drop from 158,426 ha the year before. A disappointing situation.

	Total ha
Voluntary Measure	2013	2014	2015	2014/15 change
Winter cover crop	22,543	28,472	26,454	-2,018
Brassica fodder crop	15,045	21,171	14,781	-6,390
Over winter stubbles	265,697	108,783	58,070	-50,713
Total	303,285	158,426	99,305	-59,121

Area of land under unpaid environmental management

 

At the end of 2020 I carried out a survey to get a deeper understanding of the benefits and pit falls of using cover crops, and why some farmers chose not to use them.

A total of 53 responded and, of those, 52 farmed in England; predominantly the Midlands and 1 from Scotland. Only 3 respondents said that they had never used cover crops.

Of the 50 that had used cover crops, 78% of them had used cover crops for more than 3 years.

Several reasons were given for using cover crops but 90% said it was for winter cover, and 88% used them to increase soil organic matter and improve soil structure.   Only 1 respondent said the reason for using them was to increase the yield of the following crop.

The number of cover crop species being used is fairly limited. Many (40%) used a mix suggested by their agronomist.  One or two respondents have used more unusual species such as a mix for bird seeds, sunflowers, quinoa, lupins, and camelina. Compared to previous surveys, the trend for using and continuing to use cover crops appears to be growing.  The range of crop species is limited in the UK in comparison to the US, however suppliers are responding to the challenge and beginning to offer mixes according to the function or eco service provided by the species.

The destruction of the cover crop is approached in various ways, but the majority (66%) use the herbicide glyphosate to desiccate the crop.  This is then followed by either direct drilling of the cash crop, ploughing in or min till.  The alternative methods of destruction are to roll or graze the crop. Some respondents used different methods depending on the circumstances. If frost had caused senescence for example, rolling would be used in place of spraying with herbicide.

With regards to the use of glyphosate, should we be concerned about our reliance on the herbicide? There will be cases where, in the same year, cereals are treated with glyphosate and then again to desiccate the cover crop.  Glyphosate is a herbicide used all over the world, however concerns were raised over its links to human cancer following a report published by the International Agency for Research.  It has also been linked to the decline of insect populations and causing damage to ecosystems  (Hagner et al. 2019; Druille et al. 2013; Benamú, Schneider, and Sánchez 2010).  The increased use of the herbicide has been blamed in part, on the resistance developed by some plants to the active ingredient  (Myers et al. 2016).   There is now concern over whether these effects will be compounded further by the double dose in some rotations where a cover crop is used.

The biggest barrier for not using cover crops is cost. This was also cited in the survey as one of the key drawbacks.  Many farmers have been swayed by industry ‘influencers’ that put forth the financial benefits which include an increase in yield of the follow on crop and reduced cost of chemical inputs such as fertilizer, pest and weed control.   It is indeed considered a financial risk to buy seed, establish it and later destroy it without an immediate financial reward.  Seed alone costs between £15-60/ha, with drilling between £15-40/ha(White, Holmes, and Morris 2016), €144/ha (£124/ha) in total in Europe (Commission and Environment 2019) . Across Europe, adopters of cover crops estimated fertilizer costs were reduced by 6.6% for the following crop.  Despite quantitative proof of these benefits, the financial returns are more difficult to evaluate for the reduced erosion, the improved organic matter, and increase in yield (Posthumus et al. 2015).

In the context of climate change, agricultural practices, particularly the application of chemical fertilisers, have been shown to be a significant source of emissions  (Hallsworth and Thomson 2010; DEFRA 2018; Office for Science 2011), (Abdalla et al. 2019).  One of the main benefits of cover crops is the use of certain species to fix nitrogen or catch soil nutrients preventing or reducing the leaching into water courses (Kaye and Quemada 2017; Couëdel et al. 2018; Johnson, Ellington, and Eaton 2015; White et al. 2016).  I was personally surprised that the reference to this as a benefit was not as important as other benefits.

It is encouraging to see that those farmers that are growing cover crops have embraced it year on year with many having used them for 3 years or more.  This shows a determination and long-term dedication to improving soil health and, by doing so, positively contributing to net zero carbon targets.

There are teething problems in the use, application and management of cover crops. It is still a relatively new practice in the UK and educational and technological gaps need to be addressed to encourage continued use.

As the world is looking to agriculture to become more responsible for the health of its soil and to farm more sustainably to produce nutritious food, a more sophisticated approach to cover crop planting should evolve. The future may offer an opportunity for precision planting of tailored made seed mixes, offering specific eco system services exactly where the soil needs it.

The UK has the opportunity to develop policies and incentivize cover crop use through the recently passed Agricultural Act 2020.  Bodies introducing regulations, schemes and fiscal instruments need to be mindful of prescriptive rules about the use of cover crops as this could stifle innovation and development or create unintended consequences.

Cover crops certainly play a large role in regenerative farming, working with nature to provide numerous benefits to improve our most precious of all resources: soil.