Nitrous oxide emissions from red clover and winter wheat residues depend on interacting effects of distribution, soil N availability and moisture level

The effects of residue type and distribution, soil moisture and NO3− availability were investigated in 43 days laboratory incubations (15 °C) on emissions of N2O, CO2, and for some treatments NO and NH3. Two crop residues were considered (red clover, RC, and winter wheat, WW), and they were either mixed with topsoil, placed as a discrete layer in soil, or no addition. Soil NO3− was either at ambient level or increased. Water filled pore space (WFPS) was adjusted to either 40 or 60%. All treatments were analysed for mineral N, N2O and CO2 with manual sampling and gas chromatography. Selected treatments were analysed with a continuous-flow method of N2O and CO2 by laser spectroscopy, NO by photoluminescence and NH3 by acid traps. The NH3 and NO emissions was higher in mixed RC than control and WW treatment. The N2O emission was many-fold higher with mixed than layered distribution, but only with high soil NO3− availability and high soil moisture. Emissions of N2O from WW were an order of magnitude lower compared to RC, and decomposition was slower. Both batch and continuous-flow incubations resulted in similar emissions. Disregarding the extreme emissions in the high WFPS and NO3− treatment, the N2O emission factors averaged 0.3 and 0.6% of residue N for WW and RC, respectively. Residue decomposition was enhanced by mixing, and N2O emissions by higher soil water and NO3− content. The results show the importance of residue distribution and soil condition on estimating N2O emission factors for crops.