| To meet the demands of modern agriculture,not only rice production needs increase but the use of natural resources and damage to the environment must be minimized.However,low nitrogen(N)use efficiency is a universal phenomenon in paddy field,in China.The usages of high-efficiency fertilizer and optimizing of N management method are two main means for improving N use efficiency and grain yield.As a new,eco-friendly,high-efficiency nitrogen fertilizer,polyaspartic acid urea(PASP-urea)can increase the yield of crops.Meanwhile,the effectiveness of split application of N has been demonstrated.Nevertheless,the knowledge of the mechanism by which PASP-urea and split application of N improves nitrogen use efficiency is limited.Therefore,three years field experiments were conducted to assess the effectiveness of PASP-urea and split application of N on grain yield and N use efficiency of rice,through different study sites in 2013,various N rates in 2014,and two varieties in 2015.To investigate the increasing yield and raising efficiency principle of PASP-urea and split application of N,we also evaluated the dry matter production,N accumulation,and physiological-biochemical characteristic of rice,as well as the N balance in paddy field.The main results are as follows:1.PASP-urea and split application of N(ONM,ONM-N,and ONM+N)markedly enhanced the dry matter accumulation of vegetative organs before heading stage,as well as that in panicle after heading,which resulted in the significant increase in biomass of shoot.No improvement in the redistribution of accumulated dry matter in stem plus sheath was observed by PASP-urea and split application of N.However,PASP-urea obviously developed the non-structural carbohydrate(NSC)concentration of stem plus sheath,and then promoted the remobilization of stored NSC after heading.Furthermore,the split application of N reduced the remobilization of stored NSC in stem plus sheath during heading to grain filling period,but markedly increased that during grain filling to maturity period.The logistic fitting showed that PASP-urea and split application of N postponed the times of growth rate acceleration and deceleration,while significantly increased the maximum growth rate and asymptotic maximum dry matter weight of shoot.2.The morphological and photosynthetic characteristics of leaf lamina after heading were significantly affected by urea type and N management method.Compared to conventional urea and farmer's fertilizer practice,PASP-urea and ONM treatments markedly increased the number of green leaves,leaf weight,and leaf area,which contributed to the improvement in leaf weight ratio and leaf area ratio,but reduction in spikelet to leaf area and grain yield to leaf area.PASP-urea and ONM treatments also increased the N and chlorophyll concentration of leaf lamina,as well as photosynthetic rate per unit area and per leaf lamina.Furthermore,the cumulative temperatures of leaf senescence acceleration and deceleration were increased by PASP-urea and ONM treatments,leading to the decrease in maximum senescence rate and asymptotic maximum senescence percentage of leaf lamina.So,ONM2 could increase leaf area and photosynthetic rate,postpone the senescence of flag leaf,which resulted in the improvement in photosynthesis potential after heading stage.3.Grain yield was significantly affected by urea type and N management method.PASP-urea,ONM,and ONM+N treatments markedly increased the grain yield of rice mainly by increasing panicles per unit area to improve spikelets per unit area.Moreover,compared to ONM1,ONM2 obviously increased the spikelets per panicle.The correlation analysis showed that,grain yield was significantly negatively associated with asymptotic maximum dry matter weight(R=0.97**)and biomass of shoot(R=1.0**).PASP-urea and split application of N markedly promoted the dry matter accumulation before heading.Meanwhile,the leaf senescence was postponed but photosynthetic rate was increased by PASP-urea and split application,through improving the number of green leaf lamina,leaf area,as well as N and chlorophyll concentration of leaf lamina.Furthermore,PASP-urea promoted the remobilization of stored NSC from stem plus sheath to grain after heading,while split application of N enhanced the remobilization amount of NSC in stem plus sheath during grain filling to maturity.Therefore,the dry matter accumulation of panicle after heading and grain yield were significantly developed.Moreover,no significant difference in grain yield was observed between ONM2,ONM+N1,and ONM+N2,suggesting that increase in N rate not always resulted in increasing grain yield,ONM2 was an efficient method for pursuing high grain yield.4.There were significant influences of urea type and nitrogen management method on N accumulation of rice.PASP-urea,ONM,and ONM+N obviously increased the maximum accumulation rate and asymptotic maximum N accumulation of shoot.Moreover,PASP-urea and split application of N significantly enhanced the N accumulation in organs before heading stage,as well as the distribution percentage of N in leaf lamina at heading stage.PASP-urea enhanced the activities of nitrate reductase,glutamine synthetase,and glutamate synthetase of leaf lamina after heading,as well as the concentration of free nitrate,ammonium,and amino acid of flag leaf at grain filling stage,leading to the enrichment in remobilization of N from leaf lamina to grain after heading.Meanwhile,ONM treatment not only increased the key enzymes activities of nitrogen metabolism after heading,but also improved the free nitrogen and amino acid in leaf lamina at grain filling stage,which resulted in the improvement in the N remobilization of stem plus sheath during heading to grain filling period,and that of leaf lamina during grain filling to maturity period.These finally led to the increase in N concentration of grain,panicle,and shoot.5.PASP-urea obviously promoted the N accumulation of rice,while increased the remobilization of stored N in vegetative organs by enhancing the activities of key enzymes of nitrogen metabolism,which resulted in marked increase in N accumulation of panicle and shoot.Furthermore,PAPS-urea also increased the inorganic N concentration in soil,leading to the reduction in apparent N loss from paddy filed,as well as improvement in recovery N use efficiency,agronomic N use efficiency,and partial factor productivity of applied nitrogen.Compared to FFP,ONM,ONM-N,and ONM+N treatments synchronized the N supply and demand during growing season,which led to the markedly increased N accumulation,recovery N use efficiency,agronomic N use efficiency,and partial factor productivity of applied nitrogen,as well as reduced apparent N loss.6.The three years experiments showed that:ONM2 could regulate the N balance in paddy field and enhance the inorganic N concentration in soil,which led to the significant increase in dry matter and N accumulation of rice plant.ONM2 treatment also improved the key enzymes involving in N metabolism,as well as the remobilization of accumulated NSC and N in vegetative organs.Furthermore,ONM2 treatment increased the photosynthesis potential of leaf lamina after heading,through increasing the number of green leaf lamina,leaf area,and the concentrations of N and chlorophyll in leaf lamina to postpone the senescence of leaf lamina but improve photosynthetic rate.Therefore,ONM2 significantly increased the dry matter and N accumulation in panicle,and finally improved grain yield and N use efficiency of rice. |
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