Effects Of Nitrogen Application Rate On Grain Filling Characteristics,Yield And Quality Of Rice

Rice（Oryza sativa L.）is one of the most important grain crops in China.In addition,the application of chemical fertilizer,especially nitrogen fertilizer,plays an important role in increasing rice yield per unit area and ensuring the national food security.With the improvement of living standard and consumption level,people put forward higher requirements for rice quality.The rice quality is mainly affected by the hereditary characters of varieties,cultivation techniques,water and fertilizer management and natural ecological environment,etc.The nitrogen management techniques aiming to increase the yield cannot meet the needs of fertilizer application of rice in the new era.In this paper,a two-year field trial is carried out to study the effect of nitrogen fertilizer application rate on grain filling characteristics,yield,nitrogen use efficiency and rice quality,and to explore the nitrogen fertilizer application technology based on the main quality indexes,yield and fertilizer using efficiency.The main results were showed as follows:（1）The average and maximum grain-filling rates of superior and inferior grains decreased with the increase of nitrogen fertilizer,but the active growth period of grains and the time to reach the maximum grain-filling rate increased.Compared with the treatment without nitrogen（N₀）,the maximum and average grain-filling rates of superior and inferior grains decreased by 21.2%and 31.5%,7.6%and 5.3%,respectively;the time of superior and inferior grains to reach the maximum grain-filling rate and the active growth period of grains increased by 35.8%and 8.3%,46.6%and 13.9%,respectively.The nitrogen application also increased the activities of ADPG,SBE and SSase,and promoted the starch synthesis.Compared with the treatment without nitrogen（N₀）,the total starch content of grains treated with nitrogen increased by 19.9%,15.5%,13.7%and 16.8%,respectively,after 10 d,15 d,22 d and29 d of the anthesis.（2）The nitrogen application could significantly increase the rice yields,but the yield first increased and then decreased with the increase of the nitrogen fertilizer rate.When the nitrogen fertilizer rate is 0-180 kg/hm²,the rice yield increases with the increase of nitrogen fertilizer rate,but decreases in case of continuous nitrogen application.Compared with the treatment without nitrogen（N₀）,the yield treated with nitrogen in 2018 averagely increased 1,610 kg/hm²,with an increase rate of 27.6%,and that in 2019 averagely increased 2,026 kg/hm²,with an increase rate of 39.1%.The results of yield structure components showed that the nitrogen application significantly increased the number of spikes and grains per spike,but decreased the ripening rate.Compared with the treatment without nitrogen（N₀）,the number of spikes and grains per spike treated with nitrogen increased by 32.0%and 12.5%,respectively;the ripening rate averagely decreased by 6.6%.The nitrogen application significantly increased the nitrogen absorption of rice,especially the grains.The rate of absorption and utilization of nitrogen fertilizer and agronomic efficiency decreased with the increase of the nitrogen fertilizer rate.（2）The study results showed that nitrogen fertilizer rate significantly affected the quality of rice.The increase of nitrogen fertilizer can significantly boost the brown rice rate,milled rice rate,head rice yield,length/width of head rice and protein content of milled rice,and markedly reduce the chalkiness degree,chalky rice percentage and taste value.Compared with the no-nitrogenous fertilizer treatment,the brown rice rate increased by 0.9%-3.3%by applying extra nitrogenous fertilizer,the milled rice rate increased by 1.4%-5.6%,the head rice rate increased by 5.0%-15.9%,the length/width of the head rice increased by 1.6%-6.2%,the protein content of the milled rice increased by 29.9%-91.4%,the chalkiness degree decreased by 22.8%-48.1%,the chalky rice percentage decreased by 11.9%-44.2%,and the taste value decreased by 8.0%-18.6%.The comprehensive score of all quality indexes was carried out.The comprehensive score of rice quality was the highest when the nitrogen fertilizer rate was 360 kg//hm².（3）The nitrogen application could significantly improve brown rice rate,milled rice ratio,head milled rice rate,length-width ratio of head rice and protein content of milled rice,but reduce the chalkiness degree,chalky grain percentage and taste value.When the amount of nitrogen fertilizer is 0-180 kg/hm²,the brown rice rate,milled rice rate and head milled rice rate increase with the increase of nitrogen fertilizer amount,and then continue to apply nitrogen fertilizer without significant effect.Compared with the treatment without nitrogen（N₀）,the brown rice rate,milled rice ratio,head milled rice rate,length-width ratio of head rice and protein content of milled rice treated with nitrogen increased by 0.9%-3.3%,1.4%-5.6%,5.0%-15.9%,1.6%-6.2%and 29.9%-91.4%,respectively;the chalkiness degree,chalky grain percentage and taste value decreased by 22.8%-48.1%,11.9%-44.2%and8.0%-18.6%,respectively.The results of correlation analysis of grain-filling properties and rice quality showed that the maximum and average grain-filling rates of superior and inferior grains were significantly negatively correlated with rice milling quality and significantly positively correlated with taste value;the active growth period of superior and inferior grains was significantly positively correlated with rice milling quality.Reducing the grain-filling rate and prolonging the grain-filling period could be beneficial to the improvement of rice milling quality.（4）The nitrogen application could significantly increase starch setback,but reduce peak viscosity,hot paste viscosity,breakdown viscosity,final viscosity and consistence.Compared with the treatment without nitrogen（N₀）,the starch setback treated with nitrogen averagely increased by 23.4%,and the peak viscosity,hot paste viscosity,breakdown viscosity,final viscosity and consistence decreased by 19.1%,16.3%,25.6%and 18.6%,respectively.The nitrogen application also improved the gelatinization enthalpy and degree of starch.Although the crystalline type of rice starch was not changed,the nitrogen application increased the crystallinity of rice starch,and significantly reduced the ratio of amylose to amylopectin.Compared with the treatment without nitrogen（N₀）,the gelatinization enthalpy and crystallinity of starch treated with nitrogen increased by 8.6%-16.1%and 1.8%-19.7%,respectively.The results of correlation analysis of starch properties and rice quality showed that the crystallinity was positively correlated with rice milling quality;the amylose ratio was significantly positively correlated with milling quality,exterior quality and nutritional quality,and significantly negatively correlated with taste value.（5）Based on the rice taste value,yield,nitrogen use efficiency and other key quality indexes,the recommended nitrogen fertilizer application rate is 90-150 kg/hm².Under the test conditions,the recommended nitrogen fertilizer dosage is 90-150kg/hm²,the rice taste value is 81-85,the rice yield is 7000-7500 kg/hm²,the nitrogen use efficiency is more than 40%,and the chalky grain rate of rice is 11.8%-12.9%,The protein content of milled rice is 5.99%-6.70%.