Field experiments have revealed that regular use of digestate produced by anaerobic digestion (AD) increases organic matter levels and nitrogen supply in soil.
The DC-Agri project, a four-year research scheme, studied the use of anaerobic digestate (biofertiliser) and compost across seven agricultural sites in Britain.
It found that, after three years of green and food compost applications, soil nitrogen supply increased by more than 10% and microbial activity was raised by around 5%. Microbial biomass helps to break down organic matter and release nutrients such as nitrogen and phosphorus for crop uptake. The rise in nitrogen supply also decreases the need for manufactured nitrogen fertilisers.
In the same three-year period, soil ‘shear strength’, a measure of the density and level of force required to work the soil, was decreased by a small amount across all sites.
This reduction could make cultivations easier to perform and potentially result in fuel cost savings, according to WRAP, which jointly funds the project with Defra, WRAP Cymru and Zero Waste Scotland.
The results (see graph above) show a direct link between the amount of organic matter added by compost, whether green or green/food compost, and improved soil condition.
The aim of gathering the data is to help farmers use composts efficiently, control costs and improve production.
In a written answer to an MP on 19 January, resource minister Dan Rogerson (left) said: “The Government supports recycling of green waste, including work to develop markets for quality compost.”
He added that Defra is supporting the DC-Agri scheme, which produces “an extensive knowledge exchange programme to support the use of green waste as compost”.
Mat Stewart, director of operations, feedstock and organics at Tamar Energy, said: “We are delighted to see the WRAP trial results showing that the application of digestate and green compost really does improve soil quality and make cultivations easier over the long term.
“We’re seeing the uptake of digestate use around our (AD) plants increasing, and these results are timely as we move towards the next spreading window.”
- Last year MRW reported that the Environment Agency had revised its Quality Protocol for compost, setting out when compost is no longer waste.
- WRAP has posted a video demonstrating how to use anaerobic digestate as a fertiliser.