Agronomic Performance Of Super And Ordinary Hybrid Rice Varieties Grown Under Different Level Of Nitrogen Input

Rice production in China is developing towards the goal of high yield and quality,efficient resources utilization,and environmental friendliness.Super hybrid rice?SHR?has high yield potential and strong lodging resistance,its widespread planting is of great significance for improving rice yield in China.However,farmers usually apply a large amount of nitrogen fertilizer to exert the yield potential of SHR,which would cause a large amount of nitrogen loss and a series of environmental problems.This production pattern is contrary to the concept of green rice production.Previous studies on yield potential of SHR and its physiological mechanism were usually carried out when high nitrogen input was provided,however,few studies were conducted under the condition of low or medium nitrogen input.Therefore,we conducted field experiments to compare grain yield,lodging resistance and nitrogen use efficiency?NUE?of SHR and ordinary hybrid rice?OHR?varieties,and explore the relationship between lodging resistance and NUE of rice varieties.In this study,five SHR varieties?Longliangyouhuazhan,Jingliangyouhuazhan,Yongyou2640,Yangliangyou6,Fengliangyou4?were used as experimental materials,and five OHR varieties?Quanyou6,Hanyou549,Huiliangyou858,Eliangyou476,Quanyou683?were set as contral.The three N treatments including 120?N120?,180?N180?and 270?N270?kg N ha^-1,the 180 kg N ha^-1 from local farmer's practice was set as control,the 120 and 270 kg N ha^-1 were set as the reduced N treatment and high N treatment,respectively.This work will provide useful information for breeding rice varieties with green traits and developing green crop management strategy.The results of this study are as follows:?1?Except that there was no significant difference in the yield of two variety type at N120 in 2018,the yield of SHR was significantly higher than that of OHR under the three N treatments in the two years,and it was 0.89 and 1.44 t ha^-1 higher than OHR on average in 2017 and 2018,respectively.There was no significant difference in grain yield between N120 and N180;due to lodging of N270,the grain yield decreased by 3.8%and 4.4%in2017 and 2018,respectively,of which the yield decreased significantly in 2018.The yield and yield stability of Longliangyouhuazhan and Jingliangyouhuazhan were higher than other varieties under the three N treatments.?2?Compared with OHR,the yield advantage of SHR was attributed to the higher spikelets number m^-2,grain filling percentage and dry matter accumulation.There were small differences in yield components,dry matter accumulation,and harvest index among the three N treatments,and they were inconsistent between two years.The yield advantage of Longliangyouhuazhan and Jingliangyouhuazhan was attributed to the higher spikelets number m^-2and grain filling percentage.?3?Compared with OHR,SHR had lower visual lodging score,lower lodging index,and stronger lodging resistance.The visual lodging score and lodging index increased with the increase of nitrogen fertilizer application.Among all the tested varities,Huiliangyou858,Yongyou2640 and Jingliangyouhuazhan had the strongest lodging resistance,while Quanyou683 had the weakest lodging resistance.The lodging resistance is closely related to plant height,relative height of gravity and breaking resistance of 4^thh internode from the top of plant.?4?In 2018,the nitrogen use efficiency for grain production?NUE_g?of SHR was significantly higher than that of OHR at N180 and N270,and there was no significant difference in other cases.In 2017,there was no significant difference in partial factor productivity of applied N?PFP_N?between SHR and OHR at N120 and N180;in other cases,SHR was significantly higher than OHR.Compared with N180,the NUE_g and PFP_N increased by 14.5%and 50.5%,respectively;and N270 decreased by 11.9%and36.1%,respectively.Longliangyouhuazhan and Jingliangyouhuazhan had higher NUE_g and PFP_N than other varieties under the three N treatments in two years.?5?The relationship between lodging resistance and NUE of rice varieties differs between the three N treatments.The lodging index was significantly negatively correlated with TN,but not with NUE_g and PFP_N at N120.The lodging index was significantly negatively correlated with PFP_N,but not with TN and NUE_g at N180.The lodging index was significantly negatively correlated with NUE_g and PFP_N,but not with TN at N270.Among all the tested varieties,Longliangyouhuazhan,Jingliangyouhuazhan and Yongyou2640 all showed strong lodging resistance and high NUE.In summary,compared with OHR,SHR showed higher yield and stronger lodging resistance,while its TN,NUE_g and PFP_N were not lower,which indicated that the improvement of SHR's lodging resistance did not lead to the decrease of NUE.Compared with local farmer's practice,reduced N input did not significantly reduce the yield of SHR,indicating that the realization of high yield of SHR is not necessarily dependent on high N input.Therefore,the optimization of nitrogen fertilizer management of SHR can effectively construct the green crop management strategy,and the study on the high yield,high efficiency and lodging resistant mechanism of SHR can provide theoretical guidance for breeding rice varieties with green traits.