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-ter m emissions of nitrous oxide (N2O). We performed studies on N2O emissions v arying the contents of NH4-N and microbial available organic carbon (measur ed as biological oxygen demand, BOD) of cattle slurry. Additionally the eff ect of slurry BOD on N2O emissions at different soil water contents (35, 54 , 71% water filled pore space, WFPS) was studied. Slurries from an anaerobi c digestion plant (digested slurry, BOD: 1.2 g O-2 l(-1)) or untreated slur ry (BOD: 6.8 g O-2 l(-1)) were applied at 30 m(3) ha(-1) and incubated at 2 0 degreesC. The higher the WFPS the more N2O was emitted independent from t he type of slurry applied. At low and medium soil water contents, the diges ted slurry induced significantly lower N2O emissions than the untreated slu rry. The N2O emissions were directly correlated with the BOD content of the slurry (R-2=0.61, P less than or equal to0.001). We also compared the effe ct of NH4-N concentration and BOD on emissions from the slurries at 54% WFP S. Again the BOD had a significant influence on N2O emissions but a reducti on of NH4-N had no effect on the amount of N2O emitted. The microbially ava ilable organic carbon seems to determine the amount of N2O emitted shortly after slurry application.