Study On Response And Identification Screening Of Nitrogend Utilization In Rice Genotype

Nitrogen is the largest nutrient elements in agricultural production inputs. The efficient of nitrogen is second to water for rice production, but constitute a major part of the cost of rice production inputs. The cultivation area of rice in china counted for 20% that of the world, while the application of nitrogen fertilizer in china counted for 37% that of the total global. The amount of nitrogen fertilizer use was 180 kg/hm2 on average in China's single-season paddy rice, which was about 75% higher than that of the world paddy rice. Cost of nitrogen fertilizer was as a percentage share of the total cost of external inputs as high as 35% in rice production. It will result in substantial losses and arising a series of environmental problems if that can not be absorbed by crops when nitrogen fertilizer applied into the soil.The amount of fertilizer application especially nitrogen increased as the level of grain production and yield improvement. The China's rice field has higher nitrogen fertilizer utilization and lower nitrogen use efficiency comparing with other major rice producing countries. Low nitrogen fertilizer use efficiency and a lot of nitrogen loss in Paddy rice maybe cause the waste of resources, costs of rice production increasing and increasing output without earning, at the same time lead to a series of adverse reactions. The effective way of raising rice nitrogen fertilizer use efficiency and reducing environmental nitrogen pollution is by selecting genotypes with high nitrogen use efficiency and reasonable nitrogen regulation at present. The main conclusions of this study were as follows:(1) Grain production divided the amount of nitrogen applied was defined as the nitrogen use efficiency. Production can be characterized as nitrogen use in a unified nitrogen level including the same growth period because of the nitrogen in medium including soil available nitrogen and fertilizer nitrogen more difficult to calculate. The rice could be defined as the N-efficient genotype when the rice production was higher than that of the average of the same growth period rice regardless the level of the medium nitrogen, otherwise, it would be defined as the N-inefficient genotype.174 rice genotypes would be divided into 4 kinds of type in terms of the average production under two nitrogen fertilizer levels:①Double-efficiency type, the rice production of which were both higher than the average production of the tested genotype under high or low nitrogen level.②Nitrogen-effective type, the rice production of which was lower than that of the average of the tested genotypes under low nitrogen level, and on the contrary under high nitrogen levels.③Low nitrogen-effective, the rice production of which was higher than that of the average of the tested genotypes under low nitrogen level, and on the contrary under high nitrogen levels.④Double-inefficient type, the rice production of which was lower than that of the average of the tested genotypes regardless of low and high nitrogen levels.(2) Growth period as an important agronomic traits was received a great deal of attention by rice breeders and rice producers, which was usually an important one of the breeding goals. The correlation coefficient between growing period of rice and plant growth parameters was higher under zero nitrogen level than that of nitrogen fertilizer level. It indicates that rice production under low nitrogen levels dependent on its growth period to a large extent. The relationship between biological yield and growth period of rice was highly significant positive without nitrogen application, and the relationship of which was not close under 300 kg/hm2 nitrogen level. That may be due to the longer growth period of rice, the stronger degree of dependence of plants recycling nitrogen.(3) There existed significant differences in the maximum number of tillers, effective panicles and panicle rate in different genotypes rice under two nitrogen levels.The maximum number of tillers and effective panicle increased distinctly under nitrogen applied treatments comparing with zero nitrogen treatment, but the range of increase in different genotypes was different. The total number spikelets of a panicle, seed setting rate and panicle rate declined with N fertilizer increasing, and which was consistent with the result of previous studies. From the inter-type of view, the maximum tiller number in hybrid rice increase and magnitude of the largest, but the panicle rate reduction, while japonica had the greatest increases range in effective panicles.(4) Nitrogen agronomic efficiency and nitrogen partial factor productivity were different in different genotypes under different fertilizer levels, which declined with the increase of nitrogen application. Under the same fertilizer level, the performance of different genotypes was quite different. Agronomic efficiency was 5.94kg/kg on average,0.15 kg/kg on minimum, and 27.00 kg/kg on maximum, nitrogen partial factor productivity was 27.02 kg/kg on average,9.00 kg/kg on minimum, and the maximum with 45.45 kg/kg was 4 times higher than the minimum in yield varieties. It indicated that there were a wide range genotypic differences in the tested materials.(5) There were significant genotypic differences in rice grain yield under different nitrogen levels. With 340 tested varieties, the yield of 174 varieties increased with the amount of nitrogen increases, and the yield of 70 varieties declined whatever high or low nitrogen levels, which indicating that 70 varieties was low response to nitrogen fertilizer,22 species had small production without N fertilizer and high yield performance under N conditions, which was greater response to nitrogen fertilizer degree.(6) The contribution to grain yield on yield components were different at different N levels. Effective Panicles increased significantly with the amount of nitrogen applied, panicles unit area were the greatest contribution to the yield, while the seed-setting rate and grain weight per panicle were ranked second.(7) High yield of the rice depended on the coordination development of the panicles number per unit area, the number of grain per panicle, seed-setting rate, and the 1000-grain weight.1000-grain weight was the last factor to determine yield and play a key role in the output because of its irreplaceable. Therefore, in high-yield cultivation,1000-grain weight was the main contradiction of affecting the yield. This research was studied the relationship between nitrogen and rice grain weight only from the perspective of the total nitrogen application. The results showed that nitrogen levels had some regulation on rice grain weight. However, there were significant genotypic differences in the reaction of grain weight on nitrogen. The grain weight of vast majority of varieties reduced, which of fewer varieties increased. It illuminated that rice grain weight could be regulated by different N fertilizer application, and the regulation was to be different due to the cultivars.