Effects of Combined Applications of Pig Manure and Chemical Fertilizers on CH_4 and N_2O Emissions and Their Global Warming Potentials in Paddy Fields with Double-Rice Cropping
A field experiment was carried out to study the effects of combined applications of pig manure and chemical fertilizers on CH_4 and N_2O emissions, which were measured using the static chamber/gas chromatography method, and their global warming potentials in typical paddy fields with double-rice cropping in Hunan province. The results showed that the combined applications of pig manure and chemical fertilizers did not change the seasonal patterns of CH_4 and N_2O emissions from paddy soils, but significantly changed the magnitudes of CH_4 and N_2O fluxes in rice growing seasons as compared with sole application of chemical fertilizers. During the two rice growing seasons, the cumulative CH_4 emissions for the pig manure and chemical nitrogen (N) fertilizer each contributing to 50% of the total applied N (1/2N+PM) treatment were higher than those for the treatments of no N fertilizer (0N), half amount of chemical N fertilizer (1/2N) and 100% chemical N fertilizer (N) by 54.83%, 33.85% and 43.30%, respectively (P<0.05), whilst the cumulative N_2O emissions for the 1/2N+PM treatment were decreased by 67.50% compared with N treatment, but increased by 129.43% and 119.23% compared with 0N and 1/2N treatments, respectively (P<0.05). CH_4 was the dominant contributor to the global warming potential (GWP) in both rice growing seasons, which contributed more than 99% to the integrated GWP of CH_4 and N_2O emissions for all the four treatments. Both GWP and yield-scaled GWP for the treatment of 1/2N+PM were significantly higher than the other three treatments. The yield-scaled GWP for the treatment of 1/2N+PM was higher than those for the N, 1/2N and 0N treatments by 58.21%, 26.82% and 20.63%, respectively. Therefore, combined applications of pig manure and chemical fertilizers in paddy fields would increase the GWP of CH_4 and N_2O emissions during rice growing seasons and this effect should be considered in regional greenhouse gases emissions inventory.