A trial at a Cheshire farm led by United Utilities and Compass Agronomy has shown how growing cover crops and carrying out soil analysis can reduce artificial fertiliser use to protect raw water sources.

Cover crops Cheshire trial - Mixed species cover crop.jpg

The project with Lower House Farm in Cheshire took place over two years to establish how much captured nitrogen in a cover crop’s biomass could be released for the following spring’s crop. Having this information means that a more tailored approach to fertiliser use can be used, ultimately protecting raw groundwater sources by reducing nitrate leaching risks.

The trial utilised the Soil Mineral Nitrogen (SMN) Plus system by Compass Agronomy, which estimates how much nitrogen is available in the soil and the amount likely to be mineralised from soil organic matter and incorporated crop residues.

The data can then be used to calculate how much additional nutrients are required from fertiliser, so farmers do not have the expense of over-using products which would only go unused by the crops and leach out of the soil.

Tanis Slattery-Penfold, Catchment Advisor at United Utilities, explained:

“Nitrogen leaching from soil into raw groundwater sources can have a significant adverse effect on raw water quality, that’s why we’re working with farmers and land managers across the North West to find practical and cost-effective ways to help them reduce the loss of nutrients while supporting their crops.

“We embarked on this trial with Compass Agronomy and Lower House Farm to showcase how cover crops can help protect our precious raw water resources, and also benefit farmers by improving nutrient management.”

In year one a mixed species cover crop was established on sandy loam soil, with three different sections receiving the farm’s usual practice of nitrogen fertiliser, the SMN Plus recommended treatment, or no fertiliser. Monthly soil and crop nitrogen measurements were taken during the spring and summer.

As soil nitrogen decreased, crop nitrogen content increased for both farm practice and SMN Plus treatments.

At harvest, both treatments yielded 6.7 t/ha, but the farm practice treatment recovered 208 kg N/ha compared to the SMN Plus which recovered less (166 kg N/ha) due to the slower breakdown of nitrogen from the residues.

The second year of the trial established a different mixed cover crop, with the same processes for sampling and fertiliser application. In this season, hot and dry weather conditions were a factor, likely impacting some residues not being fully incorporated into the soil.

Alli Grundy of Compass Agronomy said:

“The trial demonstrated that reducing fertiliser inputs to account for cover crop residue resulted in improved nitrogen use efficiency overall, which can lower the risk of over-application, reduce fertiliser costs and help to protect the environment from nitrogen leaching.

“Including cover crops in arable rotations and utilising SMN Plus can improve nitrogen recovery and uptake, achieve required crop yields with reduced fertiliser inputs, and result in a lower nitrogen surplus after harvest, which all contribute to improving nutrient use efficiency. These practices can help farmers and growers protect the environment and raw water quality, by reducing nitrate losses to groundwater.”

Rob Briscoe of Lower House Farm added that the trials run by United Utilities were a great benefit going forward. After several years of growing cover crops the farm had seen a marked improvement in the condition of the soil, with the added bonus of fields staying drier over winter than when left as bare stubble and less leaching of essential nutrients.

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Tanis Slattery-Penfold continued: “The results demonstrate that including cover crops in arable rotations and utilising SMN Plus can improve nitrogen recovery and uptake, achieve required crop yields with reduced fertiliser inputs, and result in a lower nitrogen surplus after harvest, which all contribute to improving nutrient use efficiency and thereby reducing the risk of nitrate leaching.

“These practices can help farmers and growers protect the environment and raw water quality by reducing nitrate losses to groundwater, while also improving nutrient use on the farm.”

The trial, and ongoing partnership working with farmers and land managers across the North West, is part of United Utilities’ holistic approach to improving river catchment land.