Study On Nitrogen Management Of Direct-seeded Rice In Double-season Rice System

Double-season rice is an important way to raise the multiple-cropping index and increase total production of rice.The traditional double-season rice with twice transplanting require high input and high labor intensity,which decreasing the farmer's enthusiasm for double-season rice production.It's an effective way to develop double-season rice by replace twice transplanted with twice direct seeded.Some rice varieties which adapt to direct-seeded in double-season were selected by Crop Physiology and Production Center of Hua Zhong Agricural University,the growth duration of these varieties are 88-100 days,and the total yield of the two season can reach to 15 t ha-1,therefore,the direct-seeded rice in double-season system(DSRS)has broad applied foreground.However,there were few studies about the nitrogen absorption characteristics and nitrogen fertilizer managements of rice varieties with short growth duration in DSRS.In order to clarify the nitrogen absorption characteristics of rice and optimize nitrogen fertilizer managements in DSRS,experiment were conducted with 16 nitrogen managements,including different nitrogen fertilizer rate and application time.The main objectives of this study were to(1)compare the differences of temperature and radiation resources between early-season and late-season in DSRS,and its' effects on the nitrogen fertilizer absorption and utilization of rice in the two seasons;(2)verify the nitrogen absorption characteristic at different stages of rice with short growth duration in DSRS;(3)explore the response of yield and it's components to different nitrogen fertilizer managements in DSRS;(4)establish high-yiled and high-efficiency nitrogen managements of DSRS.The main results of this study are as follows:1.In the DSRS,compared with the early-season rice,the average temperature and daily average radiation increased by 9.6 ? and 3.6 MJ m-2 at vegetative phase,respectively,but dereased by 3.9 ? and 1.1 MJ m-2 at grain filling stage,respectively,in the late-season rice.The differences of temperature and radiation resources between early-season and late-season changed the response of the early-season rice and late-season rice to the nitrogen fertilizer.The yields of non-nitrogen treatment in early-rice and late-season rice were 3.81 t ha-1 and 6.19 t ha-1,respectively,and the nitrogen absorption amount were 6.65 g m-2 and 10.10 g m-2,respectively.Compared with it,the average yield of the nitrogen fertilizer treatments increased by 75.4% and 13.4%,respectively,and the nitrogen absorption increased by 95.5% and 50.7%,respectively,indicating that the response to nitrogen fertilizer of early-season rice was higher than that of late-season rice.Compared with early-season rice,the average nitrogen agronomic efficiency and nitrogen physiological efficiency and nitrogen grain production efficiency decreased by 13.1 kg kg-1,26.7 kg kg-1 and 5.2 kg kg-1,respectively,in the late-season rice.2.In the early-season rice,the yield and nitrogen recovery efficiency at mid-tillering stage treatment were 10.1% and 14.9 percentage-points higher than that of seedling stage treatment with same nitrogen rate,indicating that effect of nitrogen applied at the mid-tillering stage of early-season rice was better than that of seedling stage.There was no significant difference between the two treatments of late-season rice.The application of nitrogen fertilizer at heading stage in DSRS could increase nitrogen accumulation,but had no significant effect on the yield,so there was no need to applied nitrogen fertilizer at heading stage.3.Compared with the non-nitrogen treatment,the number of spikelets per panicle of early-season rice and late-season rice at suitable nitrogen fertilizer application increased by 49.0% and 8.3%,respectively,and the accumulation of dry matter was increased by 76.2% and 12.7%,respectively,indicating that the spikelets per panicle and dry matter accumulation response to nitrogen in early-season rice was higher than that of the late-season rice.Nitrogen treatment mainly influenced rice yield by affecting the spikelets per panicle and dry matter accumulation in DSRS,and per unit area panicles number,grain filling rate and grain weight were less effect on yield.4.According to the yield performances and nitrogen use efficiency and input cost of the two years,the study has selected an optimum nitrogen management.The optimum nitrogen fertilizer rate of early-season rice was 150 kg ha-1,the propotion should be basal-fertilizer: midtilering-fertilizer: panicle initiation-fertilizer=1:1:1,and the yield could achieved 7.52 t ha-1.The optimum nitrogen rate of late-season rice was 90-120 kg ha-1,the propotion should be basal-fertilizer: panicle initiation-fertilizer=2:1 or 1:1,and the yield could achieved 7.53 t ha-1.