Cover Crop Benefits

Catchment Sensitive Farmers Meeting

I had a really fascinating day in Dorset today, exploring the use of cover crops to capture nutrients, (mainly nitrates) and stop them being washed through the soil profile and into ground water. The day was organised by Wessex Water and the Catchment Sensitive Farming organisation. Fellow Nuffield Scholar Tim Stephens and his team have put together a matrix of different cover crop species and seeding rates to look at establishment, nutrient capture and suitability within the field. The catchment also has porous dotted around the fields and every 2 weeks from October to the end of January samples are taken and the levels of nitrate in the water assessed. These values are then turned in to a Kg/Ha of nitrogen to give farmers a vital guide as to where leaching is occurring in the farming rotation and how much is being lost and when leaching occurs.

It seems that the worst leaching occurs after Oilseed Rape and Wheat, probably due to the higher levels of fertiliser they receive but also due to the very inefficient way these plants use the applied nitrogen. Wheat for example is only about 60% efficient when looking at applied or synthetic nitrogen fertiliser. Where cover crops are used the leached level of nitrogen is about 50% that of land farmed without cover crops. This has a significant impact when looking at the catchment as a whole. It is great credit to Wessex Water that they have decided to take this partnership approach to try and reduce diffuse pollution working together with the farmers in the catchment.

Beneficial and Pest Numbers in the Cover Crops

Also on hand were a team of entomologists who have been assessing the impact of cover crops on the insect population. The picture above shows the numbers of insects trapped over a 7 day period. The 2 trays on the left show the beneficial's and on the right are the pests. The top half shows the numbers and type captured in the cover crop field (oil radish and phacelia) and the bottom half shows what was captured from a control field i.e. no cover crop. This level of detail is very encouraging. This clearly demonstrates that cover crops are hosting higher insect levels all round but significantly more beneficial insects that will predate the pests. This is so important when looking at using an Integrated Farm Management approach to try and reduce the amount of pesticides we might want or need to use. There were lots of carabid beetles, who's larvae predate slugs which is also very positive. The benefits weren't just in this cover crop species mix. the photo below shows what was captured within a buckwheat, oil radish and phacelia mix. The predator list includes, carabid beetles, springtails, harvestman spiders (not really spiders at all), ants, spiders, and parasitic wasps. The pest list includes mites, flies, aphids, snails and a slug.

Beneficial Insects and Pests trapped from Cover Crops

The session continued in the local village hall with a great presentation on 'Making the Most of Cover Crops' by Ian from Oakbank. Ian talked about different cover crop mixes, how and when to establish them, and the merits of diverse mixes and the impact of this type of farming can have to the on the bottom line and the better environment. A great day of learning.