Emissions of CH₄ and N₂O under different irrigation methods and nitrogen treatments

ObjectivesThe aim of this study was to investigate the emissions, global warming potential (GWP) and comprehensive emission intensity (CEI) of CH₄ and N₂O in paddy field under different irrigation methods and nitrogen treatments, so as to obtain irrigation method and nitrogen management for reducing CH₄ and N₂O emissions from paddy soil.

MethodsIn 2015 and 2016, the field experiments of early rice and late rice were carried out in Nanning Irrigation Experimental Station. Two experiments had three irrigation methods, i.e. conventional irrigation (CIR), " thin-shallow-wet-dry” irrigation (TIR) and alternative drying and wetting irrigation (DIR), and two ratios of urea-N to pig manure-N, i.e. 100% urea-N (FM) and 50% urea-N and 50% pig manure-N (FM2). There were six treatments, i.e. CIR-FM1, TIR-FM1, DIR-FM1, CIR-FM2, TIR-FM2 and DIR-FM2. CH₄ and N₂O fluxes during the rice-growing seasons were collected using static closed chamber method and determined using a gas chromatography. Accumulative emission and GWP of CH₄ and N₂O were analyzed and CEI of CH₄ and N₂O was the ratio of GWP of CH₄ and N₂O to rice yield.

ResultsCompared to the FM1 treatment, FM2 treatment increases the early rice yield and total yields of late rice and early rice by 18.8% and 17.7% under DIR, respectively. Compared to CIR method, TIR and DIR methods increase the yield of early rice by 20.9% and 37.4%, respectively, and DIR method increases total yield of late rice and early rice by 21.5% under FM2. The CH₄ emission fluxes of late and early rice seasons in different treatments are high at the early growth stage and low at the late growth stage. During the rice-growing period, TIR and DIR methods have lower accumulative CH₄ emission from paddy field than CIR method, and FM1 treatment has significantly lower accumulative CH₄ emission from paddy field than FM2 treatment. The N₂O emission flux is negative or low at the early growth stage, and the N₂O emission from paddy field is mainly concentrated in the dramatic water change period, such as re-watering after field drying and drying at the ripening period. DIR method has significantly higher accumulative N₂O emission from paddy field than CIR method, and FM1 treatment has lower accumulative N₂O emission than FM2 treatment. There was an increase and decline relationship of CH₄ and N₂O emissions from paddy field in different treatments. The contribution of CH₄ emission to the GWP of CH₄ and N₂O was more than 99% and the contribution of N₂O emission was less than 1%. FM1 treatment decreases mole warming potential CH₄ or N₂O, GWP and CEI of CH₄ and N₂O if compared to FM2 treatment under three irrigation methods, and TIR and DIR methods reduced GWP and CEI of CH₄ and N₂O when compared to CIR method under two nitrogen treatments.

ConclusionsCompared with CIR method, TIR method increases rice yield and N₂O emission from paddy field slightly but reduces CH₄ emission, GWP and CEI of CH₄ and N₂O from paddy field, and DIR method increases rice yield and N₂O emission from paddy field but reduces CH₄ emission, GWP and CEI of CH₄ and N₂O from paddy field. Thus TIR and DIR methods are two irrigation methods in reducing GWP and CEI of CH₄ and N₂O from paddy field effectively. Compared to combined application of pig manure and urea, single application of urea reduces GWP and CEI of CH₄ and N₂O from paddy field under the two irrigation methods.