Effects of different water and fertilizer managements on greenhouse gas emissions of rice fields in Poyang Lake Basin

Abstract: Methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) are three of important greenhouse gases discharged by paddy fields. Reducing greenhouse gas emissions from paddy fields plays a crucial role in slowing global warming. In order to evaluate the influence of different water and fertilizer management modes on CH4, CO2 and N2O emissions in paddy fields and to find out a recommended mode from the perspective of reducing greenhouse gas emission and maintaining rice yield, a field experiment was carried out to determine the effects of six treatments including two irrigation methods (intermittent irrigation and flooding irrigation, referred to as W1 and W0, respectively) and three application rates of nitrogen fertilizer (0, 135, 180 kg/hm2, referred to as N0, N1 and N2, respectively) on CH4, CO2 and N2O emissions in the medium rice fields between June and September, 2019. The test site was located at the experimental base (115°58? E, 28°26? N) of the Jiangxi Province Center Station of Irrigation Experiment, in the Ganfu Plain of Poyang Lake Basin characterized by a typical subtropical and humid monsoonal climate with an annual average temperature of 18.1 ℃ and an annual average rainfall of 1 634 mm. Closed static dark chamber-gas chromatography was used to collect gas fluxes during the rice-growing seasons and measure the diurnal variation of greenhouse gases in three typical days and dynamics of CH4, CO2 and N2O emissions during the whole growth season of rice. The Global Warming Potential (GWP) was calculated based on CO2 equivalents and combined with the yields to obtain the Greenhouse Gas Emissions Intensity (GHGI) of every treatment. The results showed that diurnal variation of CH4 and CO2 emissions were similar with single-peak curves and the peak occured at noon, and N2O emissions showed a trimodal curve pattern during the typical day. The time period of 08:00-11:00 a.m. was recommended to collect gas fluxes based on analysis of correction factors at different time periods. Irrigation treatments had an extremely significant effect on the CH4 emissions during the rice growing season, and accumulative CH4 emissions under W0 were higher than that under W1. The CO2 emission of N0 treatment was lower than that of N2 and N1 under W1, and also lower than that of N2 and N1 under W0. The N2O emission of N0 treatment was also lower than that of N2 and N1 under W1, and lower than that of N2 and N1 under W0. The treatment of W0 reduced CO2 and N2O emissions compared to W1. Soil and air temperature were both important environmental factors affecting greenhouse gas emissions from paddy fields. Based on regression analysis between greenhouse gases from paddy fields and temperature, the daily emission flux and temperature of CH4 and CO2 had significant effects at the levels of 0.01 and 0.05, respectively. The sensitivity of CH4 and CO2 to soil temperature at 10 cm was higher than that of air temperature in chambers. Compared with a typical day in August, the temperature sensitivity of a typical day in September was higher, and the difference between sensitive coefficients to air temperature and soil temperature was larger. In addition, two-way analysis of variance showed that water-fertilizer interactions had an extremely significant effect on both GWP and GHGI. The treatment of intermittent irrigation combined with reduced nitrogen fertilizer application rate (135 kg/hm2) had the lowest GHGI, and thus was a recommended water and fertilizer management mode for the paddy field in the Poyang Lake Basin.