Nitrogen efficiency



Soil organic matter

The Digestate and Compost in Agriculture (DC-Agri) field experiments provide a robust evidence base to support the confident use of digestates and composts by farmers and growers as renewable fertilisers.

The research demonstrates that digestates and composts can increase yields with no negative impacts on crop quality or safety, and that compost can increase soil organic matter more quickly than other organic materials.

Importantly, the results show how farmers can make the most of the nitrogen fertiliser value in food-based digestate, but underline the high economic and environmental cost  of applying it when crops do not require nitrogen.

DC-Agri Research Summary: This accessible summary highlights the key results from the programme and explains the benefits of using digestate and compost in practice.

Food-based digestate is a valuable nitrogen fertiliser, but when applied in autumn it generally achieves only a low nitrogen use efficiency, as exemplified in the NUE graph above. Average nitrogen use efficiency in spring using a bandspreader was c. 55% of total nitrogen applied, compared with c. 15% from autumn applications. Nine years of green compost applications supplied half the organic matter supplied by almost twenty years of farmyard manure, but still resulted in a comparable increase in total soil organic matter levels, and showed that compost can build soil organic matter more quickly than other materials.


Work Package 1 (WP1) & Appendices: WP1 investigated the effects of repeat applications of compost (green and green/food) and digestate (food- and manure-based) in comparison with farmyard manure and livestock slurry on soil and crop quality at a range of experimental sites across Wales, Scotland and England.

Work Package 2 (WP2): WP2  determined  the  crop  available  nitrogen  supply  from  digestate  and quantified  the  environmental emissions to air and water from applications of digestate and compost.