Soil C and N mineralisation and agricultural value of the products of an anaerobic digestion system

Abstract

Anaerobic digestion is currently considered a valuable technology for recycling of cattle slurry due to the production of biogas, a renewable source of energy. However, an appropriate management of the waste generated from anaerobic co-digestion of cattle slurry (digestate) is needed for the sustainability of the process. This paper shows the effects provoked on soil C and N mineralisation processes and on microbial biomass due to the addition of the digestate, the liquid and solid fractions obtained after separation of the digestate and the composted solid fraction of the digestate, in comparison with the effects of the non-digested cattle slurry. Composting was a very effective way of recycling the digestate, producing highly stable (mineralised-C reached only 3% of the added total organic-C) and hygienised material with an elevated fertilising potential (the net-N mineralisation accounted for 2% of total-N from compost). The agricultural use of cattle slurry, the digestate and the separated fractions should take into account their effects on soil C and N cycles: high decomposition rate (ranging from 25% to 50% of total organic-C) and partial N immobilisation in the soil.