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There’s Still Time to Establish An Over-Winter Crop Cover

26 September 2023

This article is produced as a part of the FAS Crops & Soils Bulletin. Subscribe now to receive the full report in your inbox monthly.

As we approach late autumn, you may already have established an over-winter cover crop or green manure post-harvest, or might be considering trying to do so. As time moves on, the opportunity to successfully establish an over winter cover is diminishing, but a few species from our experience may still be appropriate.

Forage Rye and Vetch

We have routinely been successful when growing mixtures of forage rye and vetch, a small-seeded grain legume, that have been sown as late as the first couple of weeks of October near Aberdeen when the weather and soil conditions were still reasonable. This is primarily because they have large seeds which contain nutrients and energy reserves which help with germination, establishment and early growth enabling then to achieve rapid ground cover, nutrient uptake and reduced erosion risk, all key attributes associated with over-winter cover crops, even when inputs have been minimal. The feed value if grazed over winter, or utilised for an early silage cut was also quite reasonable based on lab testing of the biomass.  You may consider adding some other species to these, as a broader mixture of species generally has several advantages over a monocrop or a mix that encompasses little species diversity.

Your choice of species should ideally be dictated by soil properties and likely climate, what specific purpose you are aiming to achieve, and how long you intend to keep them in the ground before either grazing off or incorporating prior to establishment of the next crop. In terms of mixtures, they do offer some inbuilt redundancy that can provide yield stability and resilience to bad weather, and typically provide 20-40% more biomass than monocrops. Mixtures also typically provide a range of rooting structures and root biomass which can all help improve soil health, e.g. soil organic matter, soil biodiversity / worms, reduced compaction and improved drainage / water holding capacity.

Consider Legumes

Inclusion of a legume, especially if grown in a mix with non-legumes, will allow fixation of some nitrogen, especially if the crops are growing when the weather is relatively mild and there is some sunshine, so leaving a little longer if possible before incorporating can be beneficial. Inclusion of legumes can also help with increasing protein levels, for example, if one aim is to graze or make silage.

Introducing Pollinator Species

You may also be keen on bringing pollinator species into the mix, and phacelia is a classic example of this, but if grazing was also on the agenda, its not very palatable and livestock tend to graze the other species and leave it alone. It is worth noting that some species, e.g. forage rye, or others that have produced a large amount of bulk, may need a while longer (maybe 6 weeks or so) to start to break down and mineralise sufficiently once incorporated in order to reduce impacts on the establishment of the next crop.

Further Reading

If you’re looking for more information on cover crops and green manures this page has a number of links and useful resources to review. Also worth reviewing is this Subsidiary Crop Database, produced as a part of the RESAS D3 Healthy Soils Programme may also be of interest to folks interested in cover crops and green manures and what species might be suited based on growing conditions and what specific purpose you are trying to achieve.

Robin Walker, SRUC

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