Project RELACS – Improving inputs for organic farming. A high share of the nitrogen (N) in recycled and other organic fertilisers is not in a form available to plants and needs to be mineralized before plant uptake. This makes the effect on yields less predictable.

Evaluating recycled fertilisers regarding their nitrogen efficiency compared to mineral fertilisers can help estimate the amount of N they supply to the plants and, therefore, their effect on yields.

Experiments showed higher N efficiencies for stored human urine, digestates and sewage sludge than compost. Additionally, higher contents of ammonium-nitrogen (NH4 +-N) and a lower C/N ratio increase the nitrogen efficiency of recycled fertilisers.