Defra, WRAP, WRAP Cymru and Zero Waste Scotland are jointly funding a four year research project that is helping farmers maximise the potential of anaerobic digestate (biofertiliser) and compost to grow quality crops. The Digestate & Compost in Agriculture project is using a series of replicated scientific field experiments to demonstrate to farmers and advisors the agronomic, safety and business cases for using quality digestate and compost in a number of agricultural applications.
Beat the rising cost of fertiliser
Evidence from the experiments, which commenced in 2010, is already showing that the fertiliser replacement value of digestate and compost can make a significant contribution to reducing costs, particularly when compared with other commonly applied organic materials.
Digestate is a valuable source of available plant nutrients, particularly nitrogen. In fact, an impressive 80% of the total N in food-based digestate is present as readily available nitrogen, compared with around 70% for pig slurry and 45% for cattle slurry. This high level of availability means that digestate can be used as a direct replacement of ‘bagged’ nitrogen fertiliser.
Spring application best for optimum nitrogen use efficiency
The Digestate & Compost in Agriculture project is also gathering data to enable farmers to use digestate and compost more efficiently, helping control costs and improve production by including digestate in their nutrient management plans, displacing manufactured fertilisers.
When digestate was applied in spring to a potato crop at the Gleadthorpe experimental site, the crop yield data indicated that the N use efficiency was 64% of the total N applied, equivalent to manufactured fertiliser N, producing yield increases in the range 11-15t/ha above the untreated control.
At the Brawdy and Loddington experimental sites, autumn applications of digestate (and slurry) to winter wheat had much lower N use efficiencies (less than 10%) as a result of over-winter N losses through nitrate leaching. These results clearly demonstrate that, unless there is a crop N requirement in the autumn (e.g. oilseed rape), applying digestate in the spring will ensure the most efficient use of N.
In addition to measuring the nitrogen supply properties of digestate and compost, project experiments in Wales, Devon and Norfolk are measuring the greenhouse gas (ammonia and nitrous oxide) emissions to air and the leaching losses to water of nitrate, phosphorus and common indicator bacteria. Results from this research will be available late 2012/early 2013 and will contribute to helping farmers fully understand the carbon footprint of digestate and compost use and enable comparisons to be made with mineral fertilisers.
Communicating research outcomes
A key objective of the Digestate & Compost in Agriculture project is to make the research results accessible to farmers and growers through events taking place at agricultural colleges and research sites in England, Wales and Scotland.
Combining feedback on the project research data with visits to AD facilities and experimental sites, these events provide farmers and advisors with an excellent opportunity to obtain up to the minute information about digestate and its use on agricultural land.
A large number of agricultural colleges are directly involved and a suite of learning materials, including information videos, is already providing current and future farmers with the knowledge and skills to maximise the potential of quality digestate and compost to benefit their gross margins and the environment.