| Crop residue retention plays an important role in nutrient cycling of agro-ecosystem. Returning of crop residue not only reduce the residue burning-induced environmental pollution, but can also promote the agricultural sustainability. Green manuring during the fallow period is a good way to improve crop productivity and soil health. A three-year field experiment was conducted to examine the effects of different crop residue management practices during the winter fallow season on the rice grain yield, quality, soil properties and annual greenhouse gas emission in a mono-rice cropping system of central China. The experiments include six treatments: no fertilization control(CK), inorganic fertilization(NPK), rice straw burning in situ(NPK+RSB), rice straw mulching(NPK+RSM), green manuring(NPK+GM), and rice straw mulching with green manuring(NPK+RSM+GM). The main findings are given as follows:1. Compared with NPK, NPK+RSB improved the soil pH and available K content, but had no effect on soil organic carbon(SOC), total N, available N and available P content. The NPK+RSM, NPK+GM and NPK+RSM+GM significantly increased soil organic matter and total N, and had an increasing trend for available N, available P and available K with respect to NPK. The soil bulk density and porosity under all organic management treatments(NPK+RSB, NPK+RSM, NPK+GM and NPK+RSM+GM) were statistically similar with NPK during the 3-year experiment.2. Compared with NPK, all organic management treatments including NPK+RSB, NPK+RSM, NPK+GM, NPK+RSM+GM significantly increased soil catalase, urease and invertase activity. The NPK+RSM, NPK+GM and NPK+RSM+GM treatments also significantly increased soil active organic carbon(AOC) content and soil organic carbon management index(CPMI), while NPK+RSB had no effect on AOC content and CPMI with respect to NPK.3. Rice straw retention, green manuring and their combination increased the uptake and agronomic use efficiency of N, P and K in rice. Among different organic management treatments,the maximum increase in nutrient uptake and agronomic use efficiencies were recorded for NPK+RSM+GM, followed by NPK+RSM and NPK+GM.Compared with NPK, both NPK+GM and NPK+RSM+GM treatments recorded significantly higher agronomic use efficiency of nutrients(NPK) in rice. But NPK+RSB only increased uptake of K, and had no significant effect on the uptake of N and P.4. Green manuring alone or in combination with rice straw retention significantly increased the rice grain yield and enhanced the grain quality. The NPK+RSM+GM and NPK+GM were statistically similar with each other for grain yield, but these two treatments recorded significantly higher grain yield than NPK treatment during the 3-year experiment. Compared with NPK, the mean of 3 year rice grain yield in NPK+RSM+GM and NPK+GM was significant increased by 9.1% and 8.7%, respectively. The NPK+RSM and NPK+RSB were statistically at par with NPK for grain yield. The higher yield in NPK+RSM+GM and NPK+GM was attributed to more number of panicles in these treatments. The NPK+GM treatment improved the milling and cooking quality by increasing the brown rice percentage and decreasing the peak viscosity, trough viscosity, cold paste viscosity, amylase content and breakdown values. However, appearance quality attributes of rice were unaffected by NPK+GM. The NPK+RSM and NPK+RSM+GM were found to enhance the amylose content, chalky grain and chalkiness percentage compared with NPK, but such effects were not significant for most of the cases.5. Results of two annual cycles(2011–2012 and 2012–2013) for greenhouse gas emission depicted that average CH4 and N2 O emissions were 90.60–394.07 kg C ha-1 and 0.58–1.38 kg N ha–1, respectively. The proportions of CH4 and N2 O emission were 6.84%–19.85% and 13.41%–21.87% in land preparation period before rice transplanting(PBRT), 70.73%–83.39% and 31.53%–51.04% in rice growing period(PR), and 3.72%–17.99% and 29.65%–55.06% in winter fallow period(PWF), respectively. Compared with NPK, annual CH4 and N2 O emissions were increased by 1.5 folds and 94.3% in NPK+GM, 2.6 folds and 1.1 folds in NPK+RSM, and 2.4 folds and 1.2 folds in NPK+RSM+GM, respectively. Although NPK+RSB increased N2 O emissions compared with NPK but could not significantly influence on emission of CH4. The NPK+RSM, NPK+RSM, NPK+GM, and NPK+RSM+GM were statistically similar with each other regarding annual N2 O emissions.6. The net global warming potential(NGWP, kg CO2-eq ha-1 y-1) of different treatments was in order of NPK+RSM(6867) > NPK+GM(4988) > NPK+RSM+GM(4833) > CK(1979) > NPK + RSB(1644) > NPK(1136). Likewise, the greenhouse gas intensity(GHGI, kg kg-1 y-1) followed the order of NPK+RSM(0.77) > NPK+GM(0.53) > NPK+RSM+GM(0.52) > CK(0.45) > NPK+RSB(0.19) > NPK(0.13). Compared with rice straw retention alone(NPK+RSM), combination of green manuring and rice straw retention(NPK+RSM+GM) significantly reduced the net global warming potential(NGWP) and greenhouse gas emissions intensity(GHGI). |
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