Every July and August arable farmers up and down the country are harvesting their crops. In the UK we sow the next crop either in the winter or spring, so what happens to the field in between harvesting one crop and sowing the next one and how does that affect water quality?

Farmers can choose to leave a harvested field bare. However, this increases soil erosion from both wind and rain – soil needs cover to keep soil particles bound together. This soil erosion contributes to water quality problems, such as silt in our watercourses and can also lead to algal blooms as the soil particles are usually rich in nitrate and phosphate. Bare soils increase nitrate leaching as there are no roots from crops to slow down rain travelling through the soil profile.

One option is to encourage a farmer to establish cover crops, this is a crop that is planted in spring rotations and is there to provide green cover over the winter. Cover crops are planted shortly after the harvest of the previous crop. They establish before the weather turns, ensuring a green cover for when it starts to get windier and wetter, minimising soil erosion and water quality problems. You can get different species of cover crops, some are good at ‘fixing’ nitrogen to stop it leaching into groundwater. Other cover crops are good at improving the soil structure and soil health, making it a better environment for the following crop. Usually farmers use a mixture of species in the cover crop mix to get a number of benefits such as the nitrogen fixing and improving soil texture.

In January and February, these cover crops are destroyed and the crop material is left for the next crop, which means less nitrogen needs to be applied to the following crop. The residual crop material is high in readily available nitrogen, giving the next crop a nice burst of nutrients to get itself established. Whilst the cover crops are growing over the winter months, they act as carbon stores and are being evaluated for their effectiveness in helping to reduce carbon. This carbon is incorporated into the soil, rather than being released into the air. Research is also starting to indicate that carbon is useful to help nitrogen be used more effectively. Finally, cover crops provide shelter and a food source for a number of farmland birds, mammals and insects over the winter months when there would otherwise be a food shortage.

We work with farmers in our catchments to encourage them to grow cover crops, helping to improve water quality in surface water and groundwater catchments, providing carbon capture and providing essential habitat on farmlands.

Here's Nina, our senior catchment advisor, talking about cover crops in our augmented reality video. 

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Posted: 17 August 2020