Thermophilic composting of the pack can reduce nitrogen loss from compost-bedded dairy barns

Volatile nitrogen (N) loss from dairy barns is a concern. In compost-bedded pack barns, where the cattle rest on an organic pack, controlled thermophilic composting of that pack could promote microbial conversion of inorganic N (excreted by the cattle on the pack) into organic form, resulting in a reduction of pack inorganic N concentration and of volatile N loss from the barn. We tested this hypothesis during an 8-month period, including winter, on a commercial farm in the Netherlands where a specific composting method had been developed for a woodchip-bedded pack. A conversion of excreted inorganic N into organic form was assessed by repeated pack analysis; volatile N loss from the barn by calculation of its accumulating N mass balance. Our results show that volatile N loss from the barn was closely related to pack C:N ratio (P < 0.001; R²_adj. = 83 %) and was negative during the first two months of composting. The negative loss was likely the result of NH₃-absorption and/or N₂-fixation by microorganisms from ambient air, two phenomena reported in literature. The critical pack C:N ratio, at which volatile N loss from the barn was zero, was 35, in line with critical ratios found in other studies. We conclude that controlled thermophilic composting of a woodchip-bedded pack, at a relatively high C:N ratio, has potential to minimise volatile N loss from compost-bedded dairy barns.