A recent ADAS study has confirmed that cover crops can both refine nitrogen (N) usage and protect water quality.
This work was co-funded by Affinity Water and Portsmouth Water under the aegis of a project known as ‘Nitrogen release from Cover Crops’ (NiCCs).
It was centred on the identification of how best to destroy cover crops prior to the establishment of a new tillage enterprise.
During the trial, cover crops were destroyed either mechanically by rolling on a frost, chopping, or with chemicals.
Two cover crop mixes were established: one comprised phacelia and wild radish, and the other featured a mix of Japanese oats – buckwheat and phacelia.
The results secured have 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 N supply to spring cereal crops also increased by up to 35kg N/ha.
When it came to the subsequent spring cereal crop, yields following a cover crop were up by 0.2-1.0 t/ha when compared to yields, following the weedy stubble control.
Destruction of cover crops
On destruction, the cover crops released significantly more N than the no cover/weedy stubble areas.
Moving to destruction methods, chemicals were found to have more benefits than mechanical methods.
N mineral release, grain N off-take, and total crop N uptake were all higher with chemical destruction. This led to subsequent improvements in yield, and in the case of spring oats, grain weight.
However, the study did acknowledge 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.
“Cover crops can capture significant quantities of nitrogen over winter, thereby protecting surface and ground waters,” confirmed Dr. Anne Bhogal, a principal soil scientist with ADAS.
Simon Deacon from Portsmouth Water, said:
“Cover crops have been proven to reduce nitrate leaching into groundwater by up to 90%, and therefore help toward improving water quality and supply of drinking water.
“This trial provides additional information that helps toward improving cover crop management and water quality.”
Meanwhile, Catchment Water is working with farmers to find sustainable solutions which work for both crop and water production.
Dan Coffey of Catchment Water, said:
“The NiCCs trial has shown that cover crops are a vital measure for preventing nitrate leaching and demonstrating how farmers can potentially manage the destruction of cover crops to best utilise fixed nitrogen for subsequent crops.”
The results of this ADAS trial will be of significance for tillage farmers throughout the UK and Ireland.
