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. [ABSTRACT FROM AUTHOR]