| Selecting the paddy soil of red soil under double cropping in Jiangxi province, by a field experiment, the effects of four different nitrogen fertilization measures were investigated, which were the farmers practice in local (FP),20% chemical fertilizer less than FP and 20% nitrogen of the organic fertilizer substituted for the nitrogen of chemical fertilizer (T1), adding micronutrient fertilizers of Si, Zn and S on the basis of T1 (T2) and using 20% slow release nitrogen fertilizer for that of the chemical fertilizer on the basis of T2 (T3),on the influence of the rice agronomic effect and soil fertility effect. On the basis of field experiment, combined with a pot experiment by 15N tracer method, studied on the effects of the four different fertilization patterns on greenhouse gases of CO2, CH4 and N2O emissions of the paddy soil. Main results as follows:(1) The effects on rice yield, nitrogen agronomic efficiency and physiological utilization rate had no significant variation among the three different nitrogen reduction measures. Compared with FP, the nitrogen recovery rate increased by 28.13% ,45.66% and 54.84% respectively in 2013, T2 and T3 reached the significant level (p<0.05), increased by 27.41%,35.21% and 37.66% respectively in 2014, and which of the three treatments reached the significant level (p<0.05). The nitrogen partial factor productivity were increased by 18.18%,17.75% and 15.59% respectively in 2013, and by 19.97%,21.09% and 21.37% in 2014, which of the three treatments reached the significant level (p<0.05) in 2013 and 2014 respectively. Using 15N tracer the results showed that:the absorption of nitrogen in rice plants increased (p<0.05) significantly for that of the three different nitrogen reduction measures by 18.38%,11.80% and 14.82% respectively.(2) It had no significant effects on soil pH, organic matter and total nitrogen content for the three different nitrogen reduction measures respectively. Compared with the local farmer fertilization measure, the soil microbial biomass carbon content of the three different nitrogen reduction measures increased by 23.66%,25.42% and 24.17% respectively in the fourth quarter, and reached the significant level (P<0.05), and at the early rice season it was higher than that of the late rice season regularly. The content of soil microbial biomass nitrogen of three different nitrogen reduction measures increased significantly (P<0.05), the highest up to 29.91%,33.68% and 28.59% respectively in 2014. For the three different nitrogen reduction measures,it had a little bit effect on soil urease, protease and catalase activity, but the soil invertase activity increased significantly, the largest was at the early rice season in 2013, which increased by 48.24%,50.54% and 61.33% respectively, the soil protease and invertase activity had a rule that was higher at the early rice season than that of the late rice season. Soil microbial biomass carbon content showed a significant relationship with soil invertase, catalase and protease activity (P<0.01), the soil microbial biomass nitrogen content showed an extremely significant relationship with soil invertase (P<0.01), related with soil urease, catalase and proteinase activity significantly (P<0.05), and showed a significant correlation between soil microbial biomass carbon and nitrogen (P<0.05).(3) Among the three different nitrogen reduction measures, it had little effect on soil CO2 emission,but the soil N2O emissions reduced significantly, the annual cumulative emissions reduced most by T3, decreased by 43.06%,22.89% and 20.09% than that of FP, T1 and T2 respectively, all reached the significant level (P<0.05), compared with FP, the treatments of T1 and T2 which reduced significantly by 26.16% and 28.74% respectively (P<0.05). The soil CH4 emissions increased significantly by 19.38%,12.67% and 13.74% respectively (P<0.05). Compared with FP, the comprehensive influence of the greenhouse effect, that of N2O and CH4 in 100 years, T1 was 9.45% higher (P<0.05), T2 and T3 were 3.65% and 1.37% higher respectively, but there was not significant difference (p<0.05).In summary, in the treatment of T3 the rice yield and soil nutrient content was ensured sustainably, meanwhile, the rate and physiological nitrogen recycling rate improved, soil microbial biomass carbon, nitrogen content increased significantly, and it had a smallest effect on soil environment (the greenhouse effect). |
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