Effects Of Wheat Straw Returning And Different Treatments Of Fertilization And Irrigation On Rice Yield And Soil Fertility And Soil Carbon Pool

China is a populous country, which is very shortage of arable land and water resources. Rice is one of the most important food crop, large acreage, high unit yield, water and nitrogen fertilizer consumption is huge. Rice-wheat rotation is an important farming system in Yangtze River. The rice planting season is short, the pressure of wheat straw returning is heavy, improper handling can adversely affect the growth of rice. Studying the effects of wheat straw returning and different treatments of fertilization and irrigation on rice yield and soil fertility has great theoretical and practical significance for achieving rice-wheat rotation sustainable high and stable yield. In this paper, through field trials in Qinglongcun Jiangning District, Nanjing, Jiangsu Province, designed three kinds of irrigation methods (Y: flooding irrigation; Q:shallow wetlands regulation irrigation; C:conventional irrigation), three kinds of nitrogen levels (D:180kg·hm-2; Z:225kg·hm-2; G:270kg·hm-2), as well as the total amount of wheat straw returning for exploring the effect on rice yield, soil fertility and soil carbon pools. The main findings are as follows:1) Comparing wheat straw returning with no wheat straw returning, the tillers of wheat straw returning are lower than the tillers of no wheat straw returning in early tillering, but the tillers of wheat straw returning are higher than the tillers of no wheat straw returning in late tillering; the height of wheat straw returning is significantly higher than the height of no wheat straw returning; wheat straw returning can increase rice SPAD value, but this is gradually increased from heading; wheat straw returning have no significant effect on rice panicles, per panicle, seed rate,but can significantly increase grain weight and yield, the average yield increase of 4.7% in two years. Under wheat straw returning conditions and in the same nitrogen level, the rice tillers of shallow wetlands regulation irrigation treatment are lower than the flood irrigation and conventional flooded irrigation, but have no significant differences; shallow wetlands regulation irrigation helps reduce plant height, that average lower than the flood irrigation 3.47cm, a decline of 3.74%, average lower than the conventional irrigation 2.20cm, a decline of 2.4%; shallow wetlands regulation irrigation treatment will help improve rice SPAD value, thereby improving photosynthesis in rice. In the same irrigation measures, the tillers will decrease with, the amount of nitrogen, but under excess nitrogen fertilizer conditions, the total tillers will fall instead of rising; nitrogen levels have no significant effect on plant height and SPAD value. Irrigation and nitrogen levels have no significant effect on measures per panicle rice, seed rate, but shallow wetlands regulation irrigation and proper nitrogen levels can increase rice panicles and grain weight, thus improving rice yield, that compared with flood irrigated yield average increase of 8.8%, compared with conventional irrigation average yield average increase of 7.65%. When nitrogen level is 225kg·hm-2, the SPAD value and panicles and grain weight of shallow wetlands regulation irrigation are higher than other treatments.2) Comparing wheat straw returning with no wheat straw returning, wheat straw returning can not only effectively improve soil nutrient content, including organic matter SOM, TN, AK, NH4+-N, NO3--N, an increase of 10%,15.4%,2.6%,7.3%,3.6%, but also effectively improve soil Invertase activity, but will reduce the soil Urease activity and have no significant effect on soil Catalase activity. In the same nitrogen level under wheat straw returning, shallow wetlands regulation irrigation can not only effectively improve the irrigation of soil organic matter SOM, TN, AK, and NH4+-N, NO3--N content, but also can significantly improve soil Invertase activity, while will not significantly reduce the soil Urease activity, and have no significant effect on soil Catalase activity. In the same irrigation practices, soil nutrient will increase with the nitrogen levels, but excessive amount of nitrogen will reduce the soil nutrients, but the difference was not significant, it may be because nitrogen fertilizer gradient is set too low. with the in The soil NH4+-N, NO3--N will increase with the more amount of nitrogen, but when the amount of nitrogen is higher than 225 kg/hm2, an appropriate increase of nitrogen can not effectively improve the NH4+-N, NO3--N content. Nutrient status of the soil affects the activity of soil enzyme, while the activity of soil enzyme affects the nutrient status of the soil in turn, they influence each other, and ultimately affect the production of rice.3) Comparing wheat straw returning with no wheat straw returning, wheat straw returning can effectively improve soil organic carbon, soil water-soluble organic carbon and readily oxidizable organic carbon. The average increase was 8.5%,20%,7.73%. Both irrigation measures and nitrogen level can effect the soil organic carbon content, appropriate water stress will help improve the soil organic carbon content, and appropriately increasing nitrogen level also can significantly improve soil organic carbon content. Irrigation measures have significant effect on soil water-soluble organic carbon and readily oxidizable organic carbon, reducing the nitrogen level can significantly reduce the soil water-soluble organic carbon and readily oxidizable organic carbon content, but high nitrogen level, not only can not effectively improve the soil water-soluble organic carbon and readily oxidizable organic carbon content, but also may reduce the soil water-soluble organic carbon and readily oxidizable organic carbon content. When the nitrogen level is 225 kg/hm2, the soil water-soluble organic carbon and readily oxidizable organic carbon content of shallow wetlands regulation irrigation are the highest.