Swine Manure Reduces Nitrous Oxide Emissions from Acidic Red Soil Due to Mineral N Immobilization and Alleviated Acidification

Swine manure is widely used for ameliorating red soil acidification, but little information is available about its effect on N2O emissions. To explore the effects, a 35-day incubation experiment was conducted with two soils under different fertilization history: chemical fertilizers only (F) and combination of chemical fertilizers with swine manure (M). The treatments included no fertilizer (control), 100% N from urea (M0), and urea plus swine manure, which supplied 20% (M20), 40% (M40), 60% (M60), and 100% (M100) of total N. Soil N2O emission rates, pH, exchangeable acidity, mineral N species, dissolved organic carbon and nitrogen, microbial biomass carbon, and their inner relationships were examined. The N2O emission rates markedly increased following the treatments, reached peaks before day 2, and thereafter decreased sharply to the level of the control by day 25, 25, 23, 15, and 9 in F soil and by day 25, 25, 23, 19, and 11 in M soil for M0, M20, M40, M60, and M100 treatments, respectively. As swine manure application rate increased, the cumulative N2O emissions of F soil decreased significantly, while, for M soil, there was no significant difference among M0, M20, M40, and M60 treatments, which were higher than the M100 treatment. At the end of incubation, soil pH in F and M soils followed the order M0 < M20 < M40 < M60 < control < M100 and vice versa for exchangeable Al3+ and acidity. F soil had relatively higher NH4+-N concentration in M0 treatment and higher NO3--N concentrations in M0 and M20 treatments than M soil. Soil pH and NH4+-N had the greatest relative contribution to N2O emissions. Overall, this study indicates that partial chemical N replacement by swine manure could effectively mitigate N2O emissions from acidic red soil primarily because of mineral N immobilization and alleviated red soil acidification. Thus, swine manure has the potential to co-ameliorate red soil acidification and N2O emission. Further research is needed to determine the effect of swine manure on N2O emission reductions under field conditions and the overall benefit in effective N management.