CPES Cover crop trials
South Downs Chalk Groundwater Pilot
Trials were undertaken on two fields within the South Downs to determine the feasibility of cover crop establishment on shallow chalk soils ahead of a spring cash crop as a means of reducing over winter nitrate leaching.
Key findings
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Clear evidence that cover crops can reduce nitrate leaching significantly compared to over wintered stubbles.
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Weed growth on over wintered stubbles can be useful, but in terms of nitrate leaching, their performance is low.
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Broadcasting cover crop seeds into a standing crop rather than drilling after harvest appears to reduce nitrate leaching through enhanced cover crop growth.
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Where cover crops are used there appears to be an increase in the available nitrogen to the spring crop. Further research is needed to determine what other additional N will become available from the destruction of the cover crops.
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There was no effect on yield of the following cash crop from the cover cops used in this trial.
Trial 1
NICCs trials
Nitrogen release from Cover Crops trial
This project aimed to quantify the impact of different cover crop mixes and destruction techniques on over winter nitrate leaching, soil nitrogen supply and performance of the following cash crop.
Results from NICCs trials support the benefits of cover crops in capturing nitrogen that would have otherwise been lost over winter and supplying it to the following crop, enabling a reduction in N fertiliser without impacting crop yields. The study shows the importance of incentive schemes to support cover crop use so ‘harder to monetise’ benefits such as improved water quality, soil health and biodiversity can be realised.
To find out more about the trial follow follow the link to the website below:
Undersowing Mazie Trials
Portsmouth Water conducted a trial to understand and measure the benefits under sowing maize can bring in terms of nutrient retention within the soil. The trial compared undersown maize with grass vs maize bare stubble after harvest. Results demonstrated the positive impact that under sowing maize with grass can have on nitrate retention.
Other water companies and organisations have also conducted their own undersowing maize trials. See below:
Living Mulch Trials
Living mulch trials were conducted to assess if nitrogen inputs can be reduced where a clover understory was established prior to a wheat crop. There are potentially many benefits to having a living mulch such as nitrogen fixation, increased biodiversity and the opportunity to reduce inputs, but ultimately like all crops, good establishment is key to success.
Nitrogen Reduction Trial 2020-23
Portsmouth Water undertook a trial to understand and measure the effect cutting back N applications had on a crop of winter wheat in terms of yield and the reduction in nitrogen leaching into the groundwater. Yield reduction was not as drastic as expected, however a steady decline in protein levels related to the reduced nitrogen was observed. Results on nitrate leaching were inconclusive however, there was clearly elevated nitrate concentrations within the soil profile following higher N applications.
Foliar Nitrogen Trail 2020-23
This trial was to investigate the effectiveness of substituting more traditional fertilisers (granular AN, urea etc) with an alternative foliar fertiliser to potentially reduce nitrate leaching to groundwater whilst maintaining crop and economic performance. The results do not demonstrate that foliar nitrogen as a sole solution to reducing nitrogen leaching and reducing the risk of groundwater pollution. However, it has been demonstrated that a nitrogen approach encompassing polymer N products does not hinder the crop performance and economic output can be maintained.
AAN Trials
Additional Available Nitrogen trials
This trial investigates the benefits of taking AAN, alongside Soil Mineral Nitrogen (SMN) testing into consideration when nutrient management planning in terms of the potential to save costs in inputs and also reduce the amount of nitrogen applied to soils. Results showed that crops responded well despite lower nitrogen input however, concerns remain over the financial viability in applying less nitrogen in terms of potentially reducing the yield.
Trial 1
Trial 2