Effects Of Direct Sowing Rates And Panicle Fertilizer On Yield And Grain Quality In Good Tasting Rice Cultivars

Direct sowing cultivation is an important,simplified cultivation method in rice production.Seeding rate is one of the key factor affecting the yield of direct sowing rice.However,the effects of seeding rates on yield formation and grain quality of good tasting rice(GTR)cultivars has not been clearly understood.In addition,the regulating effects and physiological mechanisms of nitrogen(N)application during panicle differentiation period on yield and quality of GTR under direct sowing are also not very clear.In this study,three GTR cultivars,i.e.,Suxiangjing 3,Nanjing 5055 and Nanjing 9108 in Jiangsu province were used as materials in a field experiment during 2017-2018.Five seeding rates(60,90,120,150 and 180kghm"2)were designed at 25 cm row spacing to investigate their effects on rice yield and grain quality.The physiological reasons of N application during panicle differentiation period affecting yield and grain quality under direct sowing were analyzed from the aspects of endogenous honmone contents in rice leaves and grains and the activities of main enzymes involved in N metabolism.It is expected to provide theoretical and practical basis for high yielding in GTR under simplified cultivation.The main results were as follows:1.With the increase in seeding rate,the yields of three GTR cultivars increased first and then decreased to different extent.According to the curve equation of seeding rates and yields,the optimal seeding rates of Suxiangjing 3,Nanjing 5055 and Nanjing 9108 were 136.5,119.3 and 96 kg hm"2,respectively.The increase in seeding rate increased the panicle number per unit area(except the highest seeding rate in Suxiangjing 3),and the number of spikelets per panicle decreased with the increase in seeding rates.Total number of spikelets,filled grain percentage and 1000-grain weight increased first and then decreased with the increase in seeding rates,which was basically consistent with the changes in grain yield.The panicle size of rice was contrary to the optimal seeding rate.Appropriate reducing seeding rate in cultivars with large panicle size or increasing it in cultivars with small panicle size would be helpful to increase grain yield in direct sowing rice.2.Milling quality,including the rates of brown rice,milled rice and head milled rice of Suxiangjing 3,Nanjing 5055 and Nanjing 9108 was negatively correlated with the seeding rates,while chalky grain rate,chalkiness,protein content and setback values in rice flour were significantly or very significantly and positively correlated with the seeding rates.Gel consistency,amylose content,tasting value and breakdown values in rice flour were significantly or very significantly and negatively correlated with the sowing rates.The results showed that the milling quality and appearance quality of GTR would worsen with the increase in seeding rates.Though increasing seeding rate was beneficial to improve protein content in rice grains,it would also reduce the tasting values in GTR at the same time.3.N application during panicle differentiation period significantly increased the yields of Nanjing 9108 and Nanjing 5055,when compared with the control(no N application).Under the condition of low seeding rate(90 kg hm-2),there was no significant differences in yield between two N rates(60 kg and 120 kg N hm-2)in Nanjing 9108,which indicated that appropriate reducing N rate would not decrease grain yield.The yield was significantly reduced by high N rate(120 kg N hm-2)under high seeding rate(120 kg hm-2).As for Nanjing 5055,increasing N rate could significantly increase yield under the condition of low seeding rate(90 kg hm-2).However,further increasing N rate had no significant effects on yield under high seeding rate(120 kg hm-2),when compared with the N rate of 60 kg N hm-2.The application of panicle fertilizer significantly increased the number of spikelets per panicle of the two GTR cultivars,but the grain weight and filled grain percentage decreased in different extent,which was an important reason for the change in rice yield.4.Under the same seeding rate,the application of panicle fertilizer had no obvious effects on brown rice rate,milled rice rate and appearance quality of Nanjing 9108 and Nanjing 5055,but it significantly increased the head milled rice rate,leading to the improvement in milling quality of rice.Increasing N rate of panicle fertilizer shortened gel consistency,decreased amylose content,increased protein content in rice flour and decreased the tasting value in two GTR cultivars under direct sowing.5.The activities of glutamate dehydrogenase(GDH),glutamate synthetase(GOGAT)and glutamine synthetase(GS)in rice grains of Nanjing 9108 and Nanjing 5055 from 10-50 days after heading were positively correlated with head milled rice rate and chalkiness,but negatively correlated with gel consistency,amylose content and breakdown values,and their correlated extent varied slightly with rice cultivars.Nitrate reductase(NR)activity in rice grains had no significant correlation with other grain quality indices except its positive correlation with gel consistency of Nanjing 9108.The contents of zeatin(Z)+zeatin riboside(ZR)and indole acetic acid(IAA)in Nanjing 5055 grains were positively correlated with head milled rice rate and chalkiness,and negatively correlated with gel consistency and breakdown value in early and mid-grain filling period(10-25 days after heading).These results indicated that the main enzymes involved in N metabolism and some endogenous hormones in rice grains during grain filling had close relationships with main grain quality.Optimizing these main enzyme activities or hormone contents in grains by appropriate cultivation methods would be helpful to improve grain quality in direct sowing rice.