Abstract
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; R 2 adj. = 83 %) and was negative during the first two months of composting. The negative loss was likely the result of NH 3 -absorption and/or N 2 -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. • Pack composting resulted in low volatile nitrogen loss from a dairy barn. • Level of nitrogen loss was closely related to pack C:N ratio. • The critical pack C:N ratio of 35 was in line with ratios found in other studies. • Above this critical ratio, nitrogen from ambient air was probably fixed into the pack.
Highlights
Volatile nitrogen (N) loss from dairy barns is a concern for society and farmers
Volatilised N can eutrophicate the environment when lost as ammonia (NH3) or contribute to global warming when lost as nitrous oxide (N2O)
We studied the hypothesis that controlled thermophilic composting of a woodchip-bedded pack, with cattle housed on top, would result in a conversion of inorganic N into organic form, a reduction of pack inorganic N concentration, and a reduction of volatile N loss from the barn
Summary
Volatile nitrogen (N) loss from dairy barns is a concern for society and farmers. Volatilised N can eutrophicate the environment when lost as ammonia (NH3) or contribute to global warming when lost as nitrous oxide (N2O). All N losses, irrespective of form, reduce the amount of N cycling at farm level, which eventually results in productivity losses. N volatilisation from manure excreted in the barn results in less manure N available for feed production. The excretion gives rise to N volatilisation from the floor and from the slurry stored below. This volatilisation is predominantly in the form of NH3 (>90%) (Jungbluth et al, 2001; Misselbrook et al, 2016); the default value for total volatile N loss from Dutch freestall barns (without the cattle grazing) is 10.3% of excreted N (Van Bruggen et al, 2021)
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