Biogas Energy From Agricultural By-Products: Energy Yields and Effects on Organic Farming Systems Compared with Energy Maize Cropping

Abstract

Organic farming systems produce large amounts of organic residues suitable for biogas production. Two organic farming systems were investigated in field trials. In the dairy production system liquid manure, fodder residues, straw and cover crops were fermented. In the tested stockless farming system clover grass, straw, cover crops and in this case non marketable potatoes were used. The biogas yield potential of the stockless farming system averaged 1,742 cubic meters of methane per hectare and year, respectively 1,015 cubic meters in the tested dairy farm system. The utilisation of crop residues can replace (non-organiv) maize cropping on more than 27% of the farmland without using extra land in the stockless farming system. In the investigated dairy system, these residues correspond to approximately 16% of the farmland used for maize cropping. The energy yields and additional positive effects (higher dry matter yields of non-legume maincrops, lower nitrogen losses and a reduction of trace gas emissions) can promote the use of crop residues for digestion and the implementation of biogas plants in organically managed farms. There are some technical and economical problems regarding the implementation of the recommended systems, but the solution of these problems seems to be very profitable.