Tuesday, January 21, 2020

How to improve soil health with anaerobic digestate

December 23, 2019 by  
Filed under Crops

Cover crops can improve effectiveness of anaerobic digestate applications – and reduce nitrate leaching, suggests farmer-led research.

Growing more cover crops could help farmers capture more nitrogen from anaerobic digestate, according to the results of an Innovative Farmers field lab coordinated by Agri-TechE.  A further study has been launched to further investigate their potential.

The farmer-led trial benefits from having the support of researchers at NIAB and Cranfield University. They have already spent three years investigating how to use digestate effectively within government regulations.

Analysis

This included assessing whether cover crops could help improve soil health in combination with autumn applications of digestate – a by-product of anaerobic digestors.

Farmers from six farms took soil samples after separating their land into four different treatment areas – digestate with cover crops, digestate only, cover crops only, and a control area of neither treatment.

Soil samples were analysed at different depths across the four areas to see different treatments affect nitrogen levels. Where nitrogen sinks to lower soil levels, it potentially becomes unavailable to the next crop – and the risk of nitrate leaching into ground water increases.

Results found that often when cover crops were grown on soil after the digestate was applied, the available nitrogen was significantly reduced in all levels of the soil – and more than halved in the lower levels, indicating that the cover crops had absorbed the excess nitrogen.

Soil health

Researchers said this suggests cover crops can potentially improve soil health by increasing the effectiveness of digestate applications, reducing the risk of leaching, as well as making more nitrogen available for the farmer’s next crop.

More trials are needed to test this theory say the researchers – prompting Innovative Farmers and Agri-TechE to launch a follow-on study with sponsorship from the Agriculture and Horticulture Development Board.

Launched last autumn, this second phase is continuing to investigate how best to stabilise nitrogen so it is not released as a greenhouse gas or leaches into water. But there is also interest from the farmers to explore how digestate affects soil bacteria.

Researchers in the field lab are also providing training to help farmers carry out Visual Evaluation of Soil Structure (VESS). This is to see whether any of the different treatments have an impact on soil compaction, which would suggest an improvement in soil health.

Worm counts and green area index measurements are also being done by triallists.

Exciting results

Lydia Smith, head of NIAB Innovation Farm and the Eastern Agri-Tech Innovation Hub, said: “The early results were very exciting – often the cover crops were doing exactly what we wanted in taking up that excess nitrogen from the soil.

“Going forward we’re keen to look more closely at the nitrogen availability and at worm counts, and to get the VESS training up to scratch so farmers can help in working out how and when is best to carry out these assessments.”

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