Improving N efficiency in barley through green manure management and biogas slurry

In cereal production on stockless organic farms, green manure (GM) is commonly used to improve soil fertility. The clover-grass swards are mown frequently and the herbage is commonly mulched. The purpose of this study was to increase knowledge of the N-dynamics in such rotations, in order to suggest methods for improving N efficiency and thus organic cereal yields. The hypothesis was that spring application of biogas residue from anaerobic digestion of GM herbage increases the N uptake and yield of a subsequent barley crop, compared with repeatedly in situ mulching of the same GM herbage in the preceding season. The effect of various GM treatments on spring barley yields and nitrogen dynamics was investigated, at four sites differing in soil and climatic conditions. The results suggest that, under the Norwegian climate, mulching of GM herbage can increase cereal yields compared to its removal, depending on soil type and rotation history. However, the use of GM herbage for biogas production appears to be much more N-efficient on farm level. We applied about half of the N available in GM herbage, and the surplus residue makes it possible to manure other fields