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

Aim The effects of residue type and distribution, soil moisture and NO 3 − availability were investigated in 43 days laboratory incubations (15 °C) on emissions of N 2 O, CO 2 , and for some treatments NO and NH 3 . Methods 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 NO 3 − 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, N 2 O and CO 2 with manual sampling and gas chromatography. Selected treatments were analysed with a continuous-flow method of N 2 O and CO 2 by laser spectroscopy, NO by photoluminescence and NH 3 by acid traps. Results The NH 3 and NO emissions was higher in mixed RC than control and WW treatment. The N 2 O emission was many-fold higher with mixed than layered distribution, but only with high soil NO 3 − availability and high soil moisture. Emissions of N 2 O 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 NO 3 − treatment, the N 2 O emission factors averaged 0.3 and 0.6% of residue N for WW and RC, respectively. Conclusion Residue decomposition was enhanced by mixing, and N 2 O emissions by higher soil water and NO 3 − content. The results show the importance of residue distribution and soil condition on estimating N 2 O emission factors for crops.