Factors Affecting Nitrous Oxide Emission From Soil With Plant Residue Addition

In the context of global warming and ozone depletion, there is increasing concern over the emission of the greenhouse gas N2O. Agriculture, mainly arable soil, is the main source of the total anthropogenic N2O emission. N2O from the arable soil is produced by the nitrification and denitrification, which are regulated by many factors, such as soil water content, carbon and nitrogen sources, soil texture, and soil pH. In this study we examined the effects of those impact factors on N2O production under different soil moisture conditions. While understanding the control mechanism of N2O production, better managements can be applied on the arable soil and lead to a low N2O emission. The main results are listed as follows:1. Soil N2O production was significantly affected by soil water-filled pore space (WFPS) and plant residue C:N ratios. At aerobic conditions, soil amendments of plant materials, regardless of their C:N ratios, all enhanced soil N2O production. At oxygen-limited conditions, the N2O production was inhibited by the addition of plant residue regardless of C:N ratios. However, net N mineralization was dependent on plant material C:N ratios, being significantly higher or lower than the control for C:N ratios-15and C:N ratios>44, respectively. Such inconsistent responses indicated that nitrifiers mediating nitrification and therefore byproduct N2O production could strongly compete with heterotrophic microbes for NH4+. However, the N2O production from denitrification was mainly affected by the available N concentration.2. N2O production was affected by the soil properties. For un-amended soils, N2O production ranged from75to972ng N g-1at60%WFPS and76to8842ng N g’1at90%WFPS during the60day incubation. It was positively correlated with clay fraction (r=0.91,P<0.01) and NH4+-N concentration (r=0.82, P<0.01) at60%WFPS and appeared to be negatively associated with soil pH at90%WFPS. When soil organic C content was more than2.5%, O2availability was greater than expected with90%WFPS, suggesting that soil organic matter could regulate soil N2O emission indirectly through an effect on soil aeration. 3. N2O production was inhibited by the addition of high C:N ratio plant residue in9different soils at O2-limited condition. Under60%and90%WFPS, the addition of bermuda grass and wheat straw led to different N2O production. At60%WFPS, soil N2O production was enhanced by the addition of grass clippings, but unaffected by wheat straw. At90%WFPS, however, soil N2O production was inhibited by the addition of wheat straw, but unaffected by glass clippings.4. N2O production was affected by the addition of carbon due to the decrease of O2concentration. At40%WFPS, the O2concentration was decreased significantly after the addition of carbon source, which led to a decrease of N2O emission from the soil. But NH4+concentration had no significant effect on N2O production. At70%WFPS, while the NO3-concentration was extremely high in the soil, significant positive correlation was observed between soil N2O production and carbon addition. Also, the O2concentration decreased following the addition of soil carbon addition, and significant negative correlation was observed. Due to the effect of O2, the ratio of N2O/(N2O+N2) decreased while the carbon addition increasing.5. A meta-analysis was conducted to elucidate the effects of residue incorporation to soil N2O emission. It was concluded that (1) N2O effect size was negatively correlated with plant residue C:N ratio;(2) N2O effect size was positively correlated with total N input;(3) the highest effect size was observed in C:N ratio between60%and80%, when WFPS was above, negative effect size was observed;(4) the effect size of clay content≤10%was significantly lower than that of clay content above10%;(5) The effect size of soil pH5.8-6.4was significantly higher than those of pH below5.8and above7.8. Furthermore, There was a strong positive relationship between effect sizes of N2O and CO2emission after residue addition. Based on the sensitive index analysis, we found that the C:N ratio, WFPS and soil pH had the overalleffect compare to other factors on N2O production after plant residue addition.