Effects Cultivation Patterns On Rice Yield And Nitrogen Use Efficiency And Its Mechanisms

The rice lands are being lost drastically in recent years for the growing population and the development of the world economy, so increase rice production can not be achieved by expansion the area, but only by increase the yield per area in the future to keep the world food security. However, the grain yield and the nutrient use efficiency in most of the farmers‘ field still stays in a low level because of the biotic and abiotic stress, the unreasonable cultivation methods and fertilizer management used by farmers and so on. So the researches which armed to increase the rice production and nitrogen use efficiency by improving the cultivation patterns are needed to carry out.In order to achieve the goals which being mentioned above, we conducted a research in the field of Huaqiao Village, Wuxue City, Hubei Province during the rice growing season in 2011、2012 and 2013. Five different cultivation patterns were setted as experiment treatments, including: N0: Nitrogen omission; FP: Farmer‘s practices, MFP: Modified farmer‘s practices; SHY: Super high yielding management and MST: Muti-Split topdressing. The objectives of this experiment were: 1 to explore a cultivation pattern which can increase the rice grain yield and improve the nitrogen use efficiency in the middle reaches of the Yangtze River; 2 to identify the physiological mechanisms for increasing the yield and nitrogen use efficiency by improving cultivation patterns. The results of this research can be summarized into the following conclusions:1. The different cultivation patterns affected the rice grain yield signifcanlty. The FP showed significantly lower yield than SHY、MFP and MST, and the average yield of FP among the three years is only 8.16 t hm-2., nevertheless, the yield performance under FP changed about 12.39% among different years, which was greater than the other four cultivation patterns. The SHY, MFP and MST showed higher yield than the FP, and the average yield of these three cultivation patterns was 9.49、9.34 and 8.84 t hm-2,respectively, and the yield also changed less among different years under the SHY, MFP and MST than the FP, especially the yield of MST which changed of 5.60% among different years.2. The higher grain yield of SHY、MFP and MST was mainly attributed to the larger tillers‘ number, the larger leaf area, the higher dry matter accumulation, the larger sink size, the higher radiation use efficiency and so on, however, no significantly advantages were observed in the net photosysnthesis rate, the stomatal conductance and the intercellular carbon dioxide concentration under the SHY、MFP and MST than the FP.3. The dry matter accumulation before and after flowering stage difference significantly among different cultivation patterns. The MST、SHY and MFP showed significantly higher dry matter accumution before and after flowering stage than the FP, the average dry matter before flowering stage of MST、SHY、MFP was 10.6 t hm-2、10.7 t hm-2、9.2 t hm-2 respectively while the average dry matter after flowering of the three cultivation patterns was 7.4 t hm-2、7.8 t hm-2、7.6 t hm-2, respectively. Both of the dry matter accumulation before and after flowering stage has significantly positive relationship with the grain yield and the determination coefficient of the previous relationship is higher than the later one. The translocation of dry matter to grains among the 3 cultivation patterns was and the contribution of dry matter translocation to grains difference significantly among the 3 varieties Yangliangyou-6、Yliangyou-689 and Wandao153 was12.1%、19.0% and 5.3% while the mean value of the the contribution of dry matter translocation to grains was 13.4%、21.6% and 7.5%, difference was significantly among three cultivation patterns but not signifantly under the 5 cultivation patterns. The contribution of dry matter translocation to grain stays in a low level under different cultivation patterns indicated the dry matter accumulation after flowering plays a greater role to the grain yield.3 The different cultivation patterns affected the panicle numbers per area and the spiklets number per panicle greatly. The MST、SHY and MFP enhanced the tillers‘ number greatly than the FP during the rice vegetative growth stage, which contributed to the significantly higher panicle numbers than the FP at maturity, but the percentage of effective tillers among different cultivation patterns was not difference significantly. Nevertheless, the MST、SHY and MFP showed higher spikelts differentiation rate but lower the degenerate rate than the FP, and it was benefit to increase the rice paincle size. However, different rice varieties showed different response of spikelet differentiation and degenerate characters to nitrogen, indicated that different kinds of varieties needs different nitrogen management duing PI stage to achieve large panicle size.4. The nitrogen use efficiency changed greatly among the different cultivation patterns. The average nitrogen agronomy use efficiency under the cultivation pattern MST、MFP、SHY and FP was 17.68 kg kgN-1、13.70 kg kgN-1、12.98 kg kgN-1 and 9.27 kg kgN-1 respetively while the nitrogen recovery use efficiency of the four cultivation patterns was 63.15%、47.32%、42.30% and 28.33% respectively. The MST which topdress the N once a week achieved the highest nitrogen agronomy use efficiency and recovry use efficiency among the differernt cultivation patterns.5. The different cultivation patterns affected the rice nitrogen accumulation and the nitrogen harvest index significantly, but not affected the nitrogen translocation rate. A positive correlationship was observed between nitrogen accumulation and nitrogen recovery use efficiency although it was not significantly, which indicated that enhance the absorption bility of rice to nitrogen perhaps is an effective way to increase the rice nitrogen use efficiency. In additional, a significantly quadratic correlationship was observed between nitrogen harvest index and nitrogen recovery efficiency. When the nitrogen accumulation is about 63.8%, the nitrogen recovery efficiency achieved the maximum value.6 After spraying the solution of some exogenous hormones(GA+BR, GA+CTK) or topdressing the fertilizer KH2PO4 to the two rice varieties(Yangliangyou6 and Yliangyou689) during panicle initiation stage, we found that there were no significantly advantages in the grain yield, the yield components and the nitrogen use efficiency in the chemical regulation treatments than the control(CK) in both of the two rice varieties in our treatment. The result indicated that the technologies of chemical regulation have no significantly functions to enhance the rice yield and nitrogen use efficiency in our research.