Effects Of Nitrogen Fertilizer Management On Rice Yield,Nitrogen Use And Soil Nutrients Under Returning Wheat Straw To The Field

Rice is a safe and convenient staple food,rich in bioactive ingredients.and provides energy and nutrition for more than half of the world's population.In rice production,the role of nitrogen is irreplaceable and is an important part of the external input cost of rice cultivation.Excessive application of nitrogen fertilizer increases the risk of nitrogen loss in paddy fields,causing problems such as degradation of farmland eco-environmental quality and exacerbating the deterioration of the eco-environment.Direct return to the field is currently the most important way of returning straw to the field.At the time of mechanical harvesting,the straw is shredded and thrown back to the soil.Returning farmland not only provides the opportunity to use crop straws,but also returns nutrients such as nitrogen,phosphorus and potassium to the farmland,thereby reducing the amount of fertilizer application and improving the efficiency of fertilizer use.In order to effectively alleviate the contradiction between high yield and excessive nitrogen application in rice,the pot experiment was carried out under the condition of the total amount of wheat straw returned to the field and 7500 kg · hm-2 returned to the field in Nanjing 9108.Two nitrogen application levels were set,i.e.conventional nitrogen application(270 kg.hm'2,)and reduced nitrogen application(240 kg·hm-2).The high proportion of basal nitrogen application(basal nitrogen:tiller nitrogen:ear nitrogen=5:2:3)and high proportion of tiller nitrogen application(basal nitrogen:tiller nitrogen:fraction)Tiller nitrogen:ear nitrogen=2:5:3)two nitrogen application models were used to explore the effects of nitrogen application level and nitrogen application on rice growth,yield,nitrogen absorption and utilization,soil nutrient status and straw decomposition characteristics in the critical growth period of rice.The main results are as follows:1.Effects of nitrogen fertilizer management on rice growth under the full returning wheat straw.The effects of nitrogen fertilizer management on rice plant height,number of stems and tillers and above-ground biomass were not apparent until the middle and late stages of growth.From the booting stage,the nitrogen planting treatment of rice plant height,stem and tiller number,and above-ground biomass accelerated growth,which was significantly higher than that of the control without nitrogen application.The amount of nitrogen applied was appropriately reduced(30 kg·hm-2),and the final plant height of the rice did not decrease under the two nitrogen fertilizer management modes;the plant height of rice at different growth stages did not differ significantly between different nitrogen fertilizer management treatments.The number of stalks and tillers in the middle and early growth stages of rice under constant nitrogen application was higher than that in the case of reduced nitrogen application,and the number of stalks and tillers during rice maturity was the same between the treatments of nitrogen fertilizer.Nitrogen fertilizer treatment can promote the growth of aboveground biomass of rice.Under the same nitrogen application rate,the high proportion of tillering nitrogen treatment of rice aboveground biomass at all growth stages is higher than the high proportion of basic nitrogen treatment,and the difference is not significant.2.Effects of nitrogen fertilizer management on rice yield and its components under the full returning wheat straw.Nitrogen application significantly increased the yield of rice.The yield of nitrogen fertilizer treatment was significantly higher than that of the non-nitrogen application,with an increase of up to 33.97?40.08%,but there was no significant difference in yield between the nitrogen fertilizer treatments.The number of effective panicles,number of grains per panicle,and seed setting rate of rice during nitrogen fertilizer treatment were higher than that of the control without nitrogen application,which were increased by 27.50?30.95%,25.27?27.30%,and 13.43?18.25%,respectively.Compared with the constant nitrogen application,the reduced nitrogen application treatment not only did not reduce the rice yield,but increased slightly.The use of a high proportion of tillering nitrogen operation model is conducive to higher rice yield.3.Effects of nitrogen fertilizer management on rice nitrogen absorption and utilization under the full returning wheat straw.The wheat straw was returned to the field in full,and under the two nitrogen fertilizer management models,the reduced nitrogen application rate of nitrogen fertilizer agronomic utilization rate,nitrogen fertilizer partial productivity and nitrogen fertilizer absorption utilization rate were higher than the constant nitrogen fertilizer treatment,while the nitrogen fertilizer operation mode had little effect on nitrogen fertilizer utilization.The nitrogen content of rice organs(stems,leaves,roots,spikes)gradually decreased with the growth process of rice.Nitrogen fertilizer management can increase the nitrogen content of rice organs;the nitrogen application rate under the two nitrogen fertilizer management models was reduced by 30 kg·hm-2,Nitrogen content of rice organs have decreased to varying degrees.4.Effects of nitrogen fertilizer management on paddy soil nutrients under the full returning wheat straw.The whole wheat straw was returned to the field,and the contents of organic matter,total nitrogen,available potassium,alkali-decomposed nitrogen,and available phosphorus in the paddy soil were treated with nitrogen fertilizer.The overall trend was to gradually decrease with the growth of rice.Under the same nitrogen fertilizer management model,the nitrogen application rate was reduced by 30 kg·hm-2,which had little effect on the soil available potassium content,but the soil organic matter and alkali nitrogen content were increased;in the early and middle stages of rice growth,a high proportion of tiller nitrogen operation model was adopted The soil total nitrogen content is high.5.Decomposition of wheat straw and nutrient release characteristics.As the rice grows,the dry matter residue quality of the returning wheat straw continues to decrease,and the decay rate gradually increases.The nitrogen fertilizer management treatment at each key growth stage of rice was close to the dry matter residual quality of the wheat straw returned to the field without nitrogen application.The amount of nitrogen applied decreased and the decomposition rate of the wheat straw returned to the field decreased.The nitrogen content of high-concentration nitrogen application and high ratio of basic nitrogen treatment is higher than the phosphorus content of the wheat straw and the organic carbon content before rice maturity.The potassium content of the wheat straw under reduced nitrogen application is higher than that of the constant nitrogen application.The proportional basic nitrogen model has a relatively high nitrogen content in wheat straw.