Yield Formation And Nitrogen Response Of Yongyou Series Indica/Japonica Hybrid Rice Varieties

Rice is the staple food for more than half of the world’s population,and rice production plays a vital role in ensuring national food security.Since 1950s,Chinese rice production has kept increasing as a result of the improvement of yield per unit area.Genetic improvement is one of the most important reasons for the improvement of rice yield.Yongyou series indica/japonica hybrid rice using intersubspecific heterosis have high yield potential in rice production system.However,the promotion and application of Yongyou series varieties was limited by unstable grain filling percentage caused by the asynchronous process of superior and inferior grains.Rational nitrogen fertilizer management is conducive to promoting the grain filling process of inferior grains,maintaining high grain filling percentage of large panicle,and ultimately maximizing the yield of Yongyou series varieties.But few studies focused on the effects of real-time nitrogen management and balanced fertilization on yield performance and nitrogen use efficiency（NUE）of Yongyou indica/japonica hybrid rice.Therefore,field experiment was carried out in Qichun County,Huanggang City,Hubei Province in 2021.In this study,three indica/japonica hybrid rice varieties,Yongyou4949,Yongyou6720 and Yongyou1526,were used as experimental materials,and a hybrid indica rice variety Yangliangyou6 was set as control.The four nitrogen treatments were set including zero nitrogen(0N,0 kg N ha^-1),farmers’N-fertilizer practice(FN,180 kg N ha^-1),real-time nitrogen management（RTNM）based on chlorophyll measurement（SPAD）readings,and balanced fertilization(BN,15 kg N ha N^-1 per week),aims to explore the yield and NUE performance of Yongyou series indica/japonica hybrid rice varieties under different nitrogen treatments,and explore the agronomic mechanisms in the formation of yield,in order to provide theoretical basis for optimizing nitrogen management of indica/japonica hybrid rice.The main results are as follows:（1）The average yield of Yongyou series indica/japonica hybrid rice under different nitrogen treatments was significantly higher than that of the control cultivar Yangliangyou6,with an increase of 14.0%-89.5%.The main reason was that Yangliangyou6 was infected with rice smut and lodging under all nitrogen treatments except 0N treatment,which resulted in different degrees of yield reduction.Compared with Yangliangyou6,the yield of Yongyou series varieties increased significantly under 0N treatment,and the yield of Yongyou4949 increased by 24.5%,followed by Yongyou6720 and Yongyou1526.The yield performance trend of Yongyou series varieties under all nitrogen treatments was consistent with that under 0N treatment.Compared with FN treatment,Yongyou series varieties increased yield by 6.9%and 8.2%under RTNM and BN treatment,respectively.Yongyou4949 produced highest yield under RTNM and BN treatments,reaching 10.52 t ha^-1 and 11.02 t ha^-1,respectively.（2）In terms of yield components,compared to control variety,the yield advantage of Yongyou series indica/japonica hybrid varieties were attributed to their significantly higher spikelets m^-2 and grain filling percentage,and relatively higher spikelets per panicle contributed to the formation of higher spikelets m^-2 in Yongyou series varieties.The lower grain filling percentage of Yangliangyou6 under all nitrogen treatments was the main reason for its yield reduction.The yield advantage of Yongyou 4949 over other Yongyou series varieties depended on its stable and high grain filling percentage despite the large number of spikelets under different nitrogen treatments.In addition,high yield under RTNM and BN treatments over FN treatment were mainly due to higher grain filling percentage and grain weight.（3）In terms of material production and distribution,the higher yield of Yongyou series indica/japonica hybrid rice was attributed to the higher dry matter accumulation and harvest index at maturity,which was mainly due to stronger capacity of post-anthesis dry matter production.Longer grain filling period,suitable leaf area index,higher flag leaf SPAD value during post-flowering were the key for higher post-flowering dry matter production in Yongyou series varieties.The harvest index of Yangliangyou6 decreased significantly under all application nitrogen treatments compared with 0N treatment.The higher yield under RTNM and BN treatments than FN treatment was mainly attributed to the improvement of harvest index and dry matter accumulation at maturity differs little among nitrogen treatments.（4）In terms of NUE,compared with control variety,Yongyou series indica/japonica hybrid varieties had higher nitrogen partial productivity（PFP_N）and agronomic use efficiency（AE_N）under different nitrogen treatments.Among them,the AE_N of the control variety was negative due to the occurrence of large area disease and lodging of the N-applied rice population.Compared with FN treatment,RTNM and BN treatments significantly increased PFP_N and AE_N,and the increase of NUE was the largest under RTNM treatment.Different from yield performance,Yongyou4949 showed the best PFP_Nand AE_N only under RTNM treatment among all treatment combinations.In conclusion,Yongyou series indica/japonica hybrid varieties showed higher yield and NUE,and among them,YY4949 had more high-yield and high-efficiency characters than other Yongyou series varieties,in particular with high and stable grain filling percentage and harvest index,which is suitable for widely planting in central China.RTNM treatment increased significantly both yield and NUE under reduced N input condition,which could be considered as an optimal nitrogen fertilizer management practice for high-yield and high-efficiency cultivation of indica/japonica hybrid rice.In addition,excessive nitrogen fertilizer input may aggravate the risk of diseases,insect pests,and lodging of high-yielding rice population,therefore applying nitrogen fertilizer timely with proper quantity is the key to exploit the high yielding potential of Yongyou series indica/japonica hybrid rice.