Effects Of Controlled Release Nitrogen Fertilizer And Irrigation Regimes On Grain Yield And Nitrogen Use Efficiency And Their Physiological Mechanism In Rice

Water and nitrogen(N)are two major regulatory factors to crop growth and development.It is of great significance to realize the synergistic effect of water and N on crop yield for promoting green and efficient production of crops.Although there are some reports on the interaction between irrigation regimes and conventional available N fertilizer on rice(Oryza sativa L.)yield,little information is available about the synergistic effect of controlled-release N fertilizer and irrigation regimes on the grain yield,water use efficiency(WUE)and N use efficiency(NUE)and the mechanism in rice.In this study,two rice cultivars,namely indica in bred Yangdao 6 and japonica inbred Wuyunjing 24 were field-grown and was conducted with three N treatments,N1[100%fast-release N fertilizer(FRF),200 kg N/ha as urea],N2[100%controlled-release N fertilizer(CRF),200 kg N/ha]and N3[30%FRF+70%CRF,200 kg N/ha],and two irrigation regimes,continuously flooded(CF)and alternate wetting and moderate drying irrigation(AWMD,plants were rewatered when soil water potential reached at-10 kPa at 15-20 cm depth),were conducted under each N treatment.Biological characters,NUE and WUE of rice and soil properties were investigated under each treatment.The main results are as follows:1.Irrigation regimes and N treatments showed significant interactions on the grain yield,WUE and NUE.Among the three N treatments,the grain yield,WUE(grain yield/irrigation water)and N partial factor productivity(PFPN,grain yield/N application rate)were the lowest at N1 in both irrigation regimes,and were the highest at N2 in the CF regime and at N3 in the AWMD regime.At the same N treatment,grain yield,WUE and NUE were higer in the AWMD regime than in the CF regime.Increaseses in grain yield at N2,N3 or in the AWMD regime were mainly attributed to the increases in panicle number per meter and spikelets per panicle.Although both N2 and N3 treatments increased N accumulation in plants at maturity,they significantly decreased internal N use efficiency(IEN,grain yield/N accumulation in plants at maturity).2.In the same irrigation regime,either N2 or N3 exhibited a larger percentage of productive tillers,larger effective leaf area index,longer leaf area duration,higher N content and photosynthesis rate of leaves,higher root oxidation activity and the activities of enzymes involved in N metabolism in leaves,more dry matter accumulation in shoot and pre-stored carbon remobilization from stems during the grain filling period,and a higher harvest index comapered with N1.At the same N treatment,the AWMD regime had better above traits than the CF regime,and therefore,the treatment combination of AWMD+N3 showed the best agronomic and physiological performance among all the treatment combinations.3.Either in the AWMD or in the CF regime and at the mid and late growth stages,the CRF treatments(N2,N3)significantly increased available N content and the activities of invertase,uraese,nitrate reductase and nitrite reductase in the soil in comparison with the N1 treatment.Compared with the CF,the AWMD increased soil nitrate N content and the activities of invertase and uraese,and showed no significantly decreases in ammonium N content and activities of nitrate reductase,nitrite reductase in the soil.Among all the treatments,AWMD+N3 exihibited the most improvement in the above soil properties.In conclusion,an AWMD regime combined with the N treatment of 70%CRF+30%FRF(the total rate at 200 kg N/ha)could acieve higher grain yield and higher wate and N use efficiencies in rice.The improvement in the photosynthetic capacity of population,root activity,soil nutritions and biological properties are the important physiological and ecological reasons for the higher grain yield and higher wate and N use efficiencies in rice through synergistic interaction between the alternate wetting and merate drying irrigation and the application of controlled-release nitrogen fertilizer with a suitable proportion of fast-release N fertilizer.