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Sheep grazing on cover crops

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The research

In this field lab three farms will explore the impact of grazing sheep on over-winter cover crops on soil properties and crop performance.  They will also record management practices of livestock within an arable rotation, as well as livestock performance and health.

At the 'hub' site (representing the most applicable soil type), researchers from ADAS will undertake additional soil assessments.

Other farmers will be supported to follow the methodology of the field lab, including providing them with the trial layout and procedures to complete their own assessments.

The benefits

  • Cover cropping ahead of spring drilling can help protect soils over-winter and return organic matter.
  • Research has shown that farmers are unlikely to receive immediate financial benefit from cover cropping.
  • Grazing cover crops by sheep may help to improve gross margins by reducing feed costs and returning nitrogen in a readily available form.  It may also reduce the reliance on glyphosate to terminate cover crops.
  • However, if not managed correctly grazing can damage soil structure thereby increasing the risk of run-off and soil erosion.
  • Selecting the correct cover crop species is crucial and must consider both impacts on livestock performance and any rotational conflicts with the following cash crop.

Trial design

This farmer-managed replicated trial design will be located at three sites - one hub site plus two  'satellite' sites.

Three treatments will be carried out at each site: 
1) Cover crop grazed
2) Cover crop not grazed 
3) Stubble

Data collection at the satellite sites will be done by the farmers: species composition and biomass of cover crops (the same mix will be planted); cover crop utilisation (how much is trampled into the ground or not palatable); yield. In addition management records and diaries will be kept by the farmers to allow a cost-benefit analysis of the practice.

At the hub site, additional soil measurements will be taken by the researchers.

Latest updates

Both the hub site (Norfolk) and satellite site 2 remained involved throughout the trials. The trials compared areas of ungrazed cover crop with areas of grazed cover crop or stubble.

Interim results show a positive story for the grazed cover crop - that there was no obvious detrimental effect from grazing:

  • There were no significant differences between soil health other soil structure in the different treatments, despite being on quite wet soils.
  • The difference in VESS (visual assessment of soil structure) scores was negligible.
  • There were generally very good earthworm levels across all treatments; possibly slightly more in the grazed areas. A 'good' earthworm population is considered to be where there are 8+ earthworms per soil pit.
  • There was very good N uptake in the cover crop; grazing made the nitrogen more readily available. Although the hub site drilled the cover crop quite late - at the very end of August 2020 in sandy soil and therefore accumulated less biomass, it achieved reasonable levels of nitrogen update at 50kg N/ha. VESS scores were around 1.5 for the grazed plots (a good score). There was higher N uptake for the following spring barley in the first year of the trials (year 2 results are TBC). 
  • The sheep trod lots of cover crop biomass into the ground and ate the stalks, which are considered less palatable. Results on livestock weight gain are TBC.

The ADAS researcher is working through final harvest data at both sites. Ideally, the yield maps would correlate with the results on better N uptake in the following cash crop. At satellite site 2, there was a slightly higher yield in the following arable crop in the area cover crop treatments (with grazed cover crop areas showing the highest yields) vs those without cover crops.

The group believe that the lack of a detrimental effect on soil structure from grazing the cover crops was down to good grazing management (i.e. stocking densities, avoiding stocking in particularly wet conditions).

Cover crops (mix of mustard, vetch, phacelia, winter oats and stubble turnips) have established at all the farms.

  • Hub Site: In December, the researcher will take biomass samples of the crop, GPS those sample points and revisit once grazing has finished. Grazing to begin in January 2021.
  • Satellite site 1: The farmer was late to set up the site but has a field of stubble and cover crop (manure applied) and will start grazing in January 2021.
  • Satellite site 2: Grazing to start in late November - early December. The farmer will take on some extra assessments, including recording animal live weight and visual assessment of soil structure (VESS).
Hub site soil nitrogen assessments

August 2020

Establish cover crops on all sites

15th August 2020

Cover crop establishment assessments

30th September 2020

Cover crop biomass and quality assessments; soil assessments

15th February 2021

Yield assessments

15th August 2021

Cost-benefit analysis

30th September 2021

Group Coordinator

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AHDB

Nationwide

The Agriculture and Horticulture Development Board (AHDB) is a statutory levy board, funded by farmers, growers and others in the supply chain to help the industry succeed in a rapidly changing world. We want to create a world-class food and farming industry, inspired by and competing with the best.

Farmers

A portrait of David Cross.
David Cross

Norfolk

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