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Mar 25, 2019

Cover Crops - Six Year On

Tim Clarke reports from an event at Wexcombe Farm in February focussing on cover crops

Some arable farmers in the North Wessex Downs have been growing cover crops now for six years. The benefits of growing cover crops were always going to be long-term; those that expect yield boosts and nitrogen savings in the first year will be disappointed. As we learn more about cover crops, we are now expecting in year six to see in the soils noticeable increases in water holding capacity, in friability, in tolerance to drought and in general health.
And so when a group of NWD farmers all converged on Wexcombe Farm on Tuesday 12 February, we were expecting to see soils in good shape with good structure, increasing levels of organic matter and abundant earthworms. We were not disappointed. George Hosier, who farms at Wexcombe, has been cover cropping and direct drilling for six years now and the effects are starting to show.
One of the concerns about cover crops is whether including them in the rotation inadvertently compromises the control of blackgrass, the most pernicious grass weed. Stephen Moss, whose scientific career has been largely devoted to the study of blackgrass, gave a wide-ranging talk. He explained the various strategies that could be employed in the fight against blackgrass and it was reassuring to hear that cover crops, far from being a problem, can be part of the solution.
To finish off, Tim Clarke presented some results from an ongoing series of cover crop trials, specifically measuring nitrate concentrations in soil water.

NItrates chart

Results from porous pots have shown just how efficient cover crops are at reducing nitrate leaching. The graph above shows the concentration of nitrate in soil water at 1 metre deep underneath three different cover crops and a control of bare wheat stubble. The water underneath the stubble contained nearly 20 milligrams per litre of nitrates, as compared to the water underneath the cover crops which contained an average of 0.65 milligrams per litre. With cover crops the water leaches down, but the nitrates don’t.

The event attracted 35 farmers, agronomists, advisers and water company representatives and was organised and delivered by a partnership including the North Wessex Downs AONB, Kings Seeds, Action for the River Kennet, the Farming and Wildlife Group (FWAG SE) and Catchment Sensitive Farming.

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