A new study has confirmed that cover crops can reduce nitrate leaching by up to 90 per cent, with destruction by chemicals being most effective in terms of making nitrogen available to the following crop and for reducing weed burden.
The Nitrogen release from Cover Crops (NiCCs) project, funded by Affinity Water and Portsmouth Water and delivered by ADAS, evaluated the effect that cover crop choice and different destruction methods had on commercial farms in Hertfordshire and West Sussex. The cover crops included Phacelia & Oil Radish; and Japanese oats, Buckwheat & Phacelia with the cover crops destroyed either mechanically by rolling on a frost, chopping and incorporating, or with chemicals.
The results identified that cover crops reduced nitrate leaching losses by up to 90% when compared to the weedy stubble control. Depending on how well the cover crops established and the species mix, soil nitrogen supply to the following spring cereal crop also increased by up to 35 kg N/ha.
However, the study acknowledged that without financial incentives, it was marginally more cost-efficient for farmers to not grow a cover crop and destroy weeds chemically. It emphasised that incentive schemes should support cover crop use so ‘harder to monetise’ benefits such as improved water quality, soil health and biodiversity can be realised.
Dr Anne Bhogal, principal soil scientist at ADAS, commented; “Cover crops can capture significant quantities of nitrogen over winter, thereby protecting surface and ground waters. It has been great working with Affinity and Portsmouth water on this project which has given us new insights on how cover crop destruction method can impact the subsequent release of this nitrogen and the following crop performance.”
Danny Coffey, catchment manager at Affinity Water added; “We are working with farmers to find sustainable solutions which work for both crop and water production. The NiCCs trial has shown that cover crops are a vital measure for preventing nitrate leaching and demonstrate how farmers can potentially manage the destruction of cover crops to best utilise fixed nitrogen for subsequent crops. The data gathered through the NiCCs trial will feed into our schemes and guidance for farmers to encourage the best outcomes for both crops and water across catchments.”