Effect Of Fertilization Management On Greenhouse Gas Emissions And Soil Microbial Properties In Rice-Wheat Rotation System

The impact of greenhouse gas caused by the agricultural activities on global warming has attracted broad attention and the gas emissions from farmland could be affected by fertilization. Two field trials including equal nitrogen and optimized fertilization management experiments were designed to evaluate the effects of different fertilizer treatments on greenhouse gas emissions, soil fertility and microbial community composition in rice-wheat rotation. The equal nitrogen fertilization treatments were designed as follows: 1) no nitrogen fertilizer(CK); 2) chemical fertilizer(Urea); 3) chemical fertilizer with organic manure(Urea+OM); 4) chemical fertilizer with straw returning(Urea+SR); 5) chemical fertilizer with controlled-release fertilizer(Urea+CR). The optimized fertilization treatments included: 1) no nitrogen fertilizer(CK); 2) farmer practice(FP); 3) 25% chemical fertilizer N reduction based on FP treatment with manure and controlled-release fertilizer addition(OPT1); 4) OPT1 with straw returning(OPT2); 5) 40% chemical fertilizer N reduction based on FP treatment plus manure and controlled-release fertilizer and straw returning and all fetilizer were applied near the root zone(OPT3). The influence of different fertilization treatments on greenhouse gas emissions, soil fertility and microbial community were explored by using static opaque chamber and phospholipid fatty acid(PLFA) analysis. The main results are as follows:(1) The emission characteristics of CO2, CH4 and N2 O in wheat season were not same as that in rice season. The fluxes of CO2 of wheat season were close to that of rice season and the fluxes of CH4 in wheat season were smaller than that in rice season, while the fluxes of N2 O showed opposite tendency. Compared to CK, fertilization treatments could increase the seasonally cumulative fluxes of CO2, CH4 and N2 O. The organic manure treatments furhter increased the seasonally cumulative fluxes of the three greenhouse gas and the controlled-release fertilizer decreased them. While the straw returning increased the seasonally cumulative fluxes of CO2 and CH4, but the fluxes of N2 O was reduced.(2) The results of Global warming potential(GWP) with CH4 and N2 O showed the overall assessment of the GWP was dominated by N2 O emissions in wheat season and by CH4 in rice season. CH4 emission contributed most of the GWP of the whole wheat-rice rotation, thus mitigation of CH4 emissions was priority to the reduction of greenhouse gas emissions. Among the equal N fertilizer treatments, chemical fertilizer plus manure, chemical plus straw return and chemical plus controlled-release fertilizer could increase the grain production compared to the chemical fertilizer. In the optimized fertilizer treatments, OPT1, OPT2 and OPT3 treatments produced a higher yield than conventional fertilization, in which OPT1 treatment showed the most significant effect and OPT3 treatment could save 40% of chemical N.(3) Combined the GWP with crop yield under different fertilizer treatments in rice-wheat rotation(GHGI), the GHGI of Urea+OM and Urea+CR were lower than in Urea, therefore, they had advantages over the chemical treatment in the GHGI assessment system. In the optimized fertilizer treatments, OPT1 and OPT2 treatment not only increased the yield but also decreased the GWP per unit output.(4) Correlation analyses of greenhouse gas emissions with soil factors in equal nitrogen and optimized fertilizations indicated that there was a highly significant correlation between CO2 emissions and soil temperature(p<0.001), and CH4 could be affected by soil temperature and soil water content in rice season. Besides, the emissions of CO2, CH4 and N2 O correlated with NH4+-N, NO3--N, Urease, soil biomass C and N in different stages. The relationships differed in various stages.(5) The PLFA analysis showed G+ and actinomycetes were the dominant microbial groups in paddy soil. Among the equal nitrogen fertilizer treatments, Urea+OM could improve total PLFAs abundance with a relatively higher fungi/bacteria ratio and lower the G/G ratio, which indicated soil conditions and ecosystem buffering capacity was improved by OM application. Compared with CK and FP treatments, OPT3 enhanced total PLFAs abundance and improved ecosystem buffering capacity of paddy soil with relatively higher fungi/bacteria ratio. PCA analysis showed that fertilizer managements affected soil microbial community composition. The abundances of gram-positive bacteria and actinomycetes were strongly affected by the fertilization optimized OPT3, amounts of gram-negative bacteria and fungi were mainly affected by OPT2 treatment.