NITROUS OXIDE EMISSION AND PRODUCTION PATHWAYS UNDER ALTERNATE WETTING-DRYING CONDITIONS IN RICE PADDY SOILS

The aim of this study was to evaluate the relative contributions of nitrification and denitrification in rice paddy soils under various water events. A laboratory incubation study was conducted in China to quantify N2O production during alternate wetting and drying cycle (AWD) versus permanent flooding (PF). The soils were treated with long-term chemical fertilizer (CF); chemical fertilizer plus pig manure (PMCF); and chemical fertilizer plus rice straw (SRCF) for 5 years. The results showed that N2O flux during AWD was consistently higher than PF. The highest N2O flux during AWD was 1.94 mg m(-2) h(-1). The PMCF and SRCF soils had higher N2O emissions compared to CF and CK soils. Ammonia oxidizer community peaks were found at 60% field capacity (FC) (p < 0.0001), while, for denitrifier, this increase was maintained for a certain period of time (10d) and then started to decrease. Autotrophic nitrification appeared to be an important and dominant process of N2O emissions during AWD and PF, contributed 79.03% of N2O emissions during AWD, while 36.53% during PF. Thus, the results concluded that under AWD event the addition of pig manure and rice straw plus chemical fertilizer significantly increased the N2O flux, by stimulating the growth of microbial communities.