Effect Of Controlled Release Nitrogen Fertilizer Management On The Grain Yield And Nitrogen Use Efficiency Of Rice And Its Mechanism

Controlled-release nitrogen fertilizer is considered as one of the most important new fertilizers both domestically and internationally.This type of fertilizer has a slow release rate,an extended release period,and requires fewer topdressing applications.As a result,it can effectively reduce nutrient deficiencies in the middle and late stages of crop growth,and prevent nutrient from loss in paddy fields,and minimize the risk of environmental pollution.Additionally,it can help farmers save fertilizer costs and reduce labor requirements.Most studies examining the effects of controlled-release nitrogen(N)fertilizer on rice yield and N use efficiency have focused on comparing one-time application of controlled-release N fertilizer with several applications of rapid-release N fertilizer.However,there is limited information available on the effects of different management methods for controlled-release N fertilizer on root and shoot morpho-physiology and soil properties,as well as their relationships with the grain yield and N use efficiency(NUE).The underlying mechanism remains unclear.It is important to address these issues in order to achieve high yield and high efficiency in rice cultivation.In this study,we investigated the effects of different nitrogen application treatments on two rice varieties,Yongyou 2640(indica/japonica hybrid rice)and Jinxiangyu 1(conventional japonica rice variety),in a field experiment.Seven nitrogen application treatments were conducted,including nitrogen omission(T1),rapid-release N fertilizer(RRNF)(T2,270 kg N hm-2),controlled-release N fertilizer(CRNF)before transplanting(T3,270 kg N hm-2),reduced application rate of RRNF(T4,240 kg N hm-2),reduced application rate of T3(T5,240 kg N hm’2),one-time application of 70%CRNF+30%RRNF(T6,240 kg N hm-2),and one-time application of 70%CRNF+30%RRNF(T7,with rapid-release N fertilizer applied at basal and panicle initiation time at a ratio of 1:1,respectively,totaling 240 kg N hm-2).We investigated the effects of these controlled-release N fertilizer management methods on rice yield and nitrogen use efficiency,as well as their underlying mechanism.The main results are as follows:1.Compared to the T2 treatment,the T3,T5,T6,and T7 treatments significantly increased grain yield for both rice varieties.The T6 and T7 treatments had the highest yield performance,while the T4 treatment had a yield performance comparable to the T2 treatment.The increase in grain yield for the different CRNF management methods was due mainly to increased total spikelets.The total N uptake,agronomic N use efficiency,partial factor N productivity,and N recovery efficiency of both varieties were increased,but the internal N use efficiency and physiological N use efficiency were decreased by the CRNF management methods(T3,T5,T6,and T7).Moreover,the T4 treatment significantly improved partial factor N productivity and N recovery efficiency.2.The percentage of productive tillers,leaf area index,green leaf area duration,root oxidation activity,above-ground dry matter accumulation,root dry weight,root length,root surface area,activities of enzymes related to N metabolism,root oxidation activity,and organic acid contents of root exudation under CRNF management methods were significantly higher than those under RRNF treatments.Meanwhile,the abovementioned agronomic and physiological traits were strongly correlated with grain yield,total N uptake,agronomic N use efficiency,partial factor N productivity,and N recovery efficiency.Furthermore,the T6 and T7 treatments exhibited the best agronomic and physiological performance.3.Compared to the RRNF treatments(T2 and T4),the CRNF treatments(T3,T5,T6,and T7)significantly increased soil available N content,soil urease activity,and soil organic matter content at the middle and late stages for both rice varieties.Among all the treatments,T6 and T7 showed the greatest improvement in soil properties.Furthermore,the enhanced abundance and expression of Nitrosospira were observed in the CRNF mixed with RRNF compared to the RRNF treatment through 16s rRNAhighthroughput sequencing,which promoted the conversion of ammonium-N to nitrate-N,and increased the retention of available N in the soil,enhanced N uptake,and resulted in higher N recovery efficiency.In conclusion,the combination of CRNF(70%)with RRNF(30%)(T6 and T7)had better effects on grain yield and N use efficiency in rice than RRNF,and there was no significant difference between T6 and T7 treatments,but T7 should be followed by protective fertilizer.Therefore,a single application of CRNF(70%)+RRNF(30%)(T6)is the best way to improve rice yield and nitrogen use efficiency,as well as agricultural green and efficient development.The improvement of population quality,root morphophysiology,soil nutrients,and Nitrosospira abundance are the key factors contributing to the higher grain yield and higher NUE.