The effect of biological oxygen demand of cattle slurry and soil moisture on nitrous oxide emissions

The application of animal manure slurries to soils may cause high short-term emissions of nitrous oxide (N2O). We performed studies on N2O emissions varying the contents of NH4-N and microbial available organic carbon (measured as biological oxygen demand, BOD) of cattle slurry. Additionally the effect of slurry BOD on N2O emissions at different soil water contents (35, 54, 71% water filled pore space, WFPS) was studied. Slurries from an anaerobic digestion plant (digested slurry, BOD: 1.2 g O2 l−1) or untreated slurry (BOD: 6.8 g O2 l−1) were applied at 30 m3 ha−1 and incubated at 20°C. The higher the WFPS the more N2O was emitted independent from the type of slurry applied. At low and medium soil water contents, the digested slurry induced significantly lower N2O emissions than the untreated slurry. The N2O emissions were directly correlated with the BOD content of the slurry (R2=0.61, P≤0.001). We also compared the effect of NH4-N concentration and BOD on emissions from the slurries at 54% WFPS. Again the BOD had a significant influence on N2O emissions but a reduction of NH4-N had no effect on the amount of N2O emitted. The microbially available organic carbon seems to determine the amount of N2O emitted shortly after slurry application.