Effects Of Optimizing Nitrogen Managent Practice On Population Productivity In Rice-wheat Cropping System

To alleviate the pressure of population growth and economic development of the demand for food,especially in the form of reduction of cultivated land area and the expansion of grain acreage,increasing crop yield has become an important way to guarantee food security.The establishment of soil-plant-environment optimization,synchronous crop yield and fertilizer efficiency has become one of the important measures for sustainable development of agriculture.This experiment conducted from 2014 to 2015 in a long-term experiments site in the Agriculture Science Research Institute of Rugao of Jiangsu.five treatments were designed as follows:CK(No fertilizer),FFP(Farmer’s fertilizer practices),andoptimized fertilizer management including:Super high yield,(SHY),High yield and high efficiency(HYHE)and HYHE substitute nitrogen(HYHE-SN).This study aimed to investigate the effects of nitrogen fertilizer management on biomass,yield,N accumulation,N transport,physiological characteristics and the relationships between them in rice and wheat plants,which would provide the theoretical basis for the high yield and high efficiency fertilization technology and practical guidance for the high yield and high yield production of rice wheat rotation system.The main findings are as follows:1.In Jiangsu Province,a high yield was still maintained in treatments with reduced N supply amount.Compared with FFP,three optimized fertilization treatments increased by 17.03%,14.14%and 7.05%in yield respectively andSHY obtained the highest yield which waswith 9325 kg hm-2.In wheat season,the yield of SHY was 6695 kg hm-2 and 9.57%higher than that in FFP.Application of nitrogen fertilizer increase the yield of grains per spike,seed setting rate and 1000 grain weight,while decrease the spike number in rice plant,and the increased yield in wheat plant was attributed to the increased spikes number,grains per spike andl000 grain weight.2.Nitrogen optimal management significantly improved nitrogen utilization efficiency in rice and wheat.The AEN,REN and PFPN of FFP treatment were significantly lower than those of SHY,HYHE and HYHE-SN,and the AEN,REN of HYHE treatment were higher than other treatments.Compared with FFP treatment,the AEN,REN and PFPN were increased by 53.79%,30.38%and 38.87%respectively.Due to the large amount of nitrogen fertilizer in rice season,the REN was only 35.9%in FFP,which was significantly lower than the optimized fertilization treatments,and the AEN and PFPN of FFP were significantly lower than that of optimal treatment,the nitrogen use efficiency of inorganic nitrogen fertilizer decrease with increasing nitrogen fertilizer application.The queue of AEN and REN in optimum treatment is HYHE>SHY>HYHE-SN,the queue of PFPN is HYHE>HYHE-SN>SHY.REN of SHY,HYHE and HYHE-SN increased by 54.3%,67.4%and 46.2%than that of FFP.The AEN,REN and PFPN of FFP treatment were significantly lower than that of SHY and HYHE in wheat season.The AEN and REN of inorganic nitrogen fertilizer showed a decreasing trend with the increase of nitrogen application rate.The REN of HYHE-SN treatment were lower than those of other nitrogen treatments.The queue of REN is HYHE>SHY>FFP>HYHE,The REN of HYHE-SN and SHY was increased by 7.73%and 29.08%thanthat in FFP.3.Optimized nutrient management actualized a bettwe N allocation and distribution in rice plant,which functioned through reducing the proportion of nitrogen uptake in the early stage of crop growth,and increasing the proportion of nitrogen accumulation in the later growth stages.The different nitrogen absorption model increased the dry matter production of rice and wheat in the later growth stages,and improved crop yield ultimately.The mean values of biomass accumulation in rice transplanting to tillering,tillering to jointing,jointing to flowering and flowering to harvesting stages were 11.22%,18.90%,25.40%and 44.48%.The biomass accumulation from transplanting to tiller and tiller to jointing were significantly lower in optimized nutrient management treatments than that in FFP treatment,and the biomass at the flowering and maturity was significantly higher in optimized nutrient management treatments than in FFP treatment,which indicated that FFP treatment was beneficial to the biomass accumulation in earlier stages of the rice.The averaged values of biomass accumulation in wheat transplanting to tillering,tillering to jointing,jointing to flowering and flowering to harvesting stages were 11.8%,10.2%,24.6%and 53.3%.The biomass in FFP treatment from transplanting to tiller satge was significantly higher than that in the optimized fertilization treatment,while it was significantly lower than the optimal fertilization treatment from the flowering to mature stage in FFP treatment.The optimization of nitrogen fertilizer could improve the population growth index of rice and wheat.FFP treatment promoted the crop growth in the early stage,which was decreased at late stages due to the decreased nitrogen supply and decreased photosynthesis,and indfluencethe formation of crop yield ultimately.In summary,The optimized management achieve high yield and high nitrogen use efficiency of rice,which was actualized by controlling the total amount of nitrogen fertilizer and distributing them in different growth stages,increased nitrogen supply amount after flowering stage maintain a high photosynthetic rate level and delay sencence,which was not only conducive to the production of assimilates,but also to promote the transfer of photosynthetic products to spike,increase capacity and grain-filling rate,and increase crop yield.