Effects Of Combined Application Of Organic And Inorganic Fertilizers On Nitrogen Utilization Of Winter Wheat And Soil Carbon And Nitrogen Dynamics In Guanzhong

In order to pursue sustainable high yield and meet the increasing food demand,the phenomenon of excessive application of nitrogen fertilizer in agricultural production is becoming more and more serious,and the contradiction between crop high yield and farmland ecological environment cannot be ignored.Combined application of organic and inorganic fertilizers is considered to be an effective way to achieve sustainable agricultural development.However,different studies on the optimal ratio of organic and inorganic fertilizers often have different measurement standards,which usually only consider a single factor such as yield,soil nutrients,greenhouse gases,etc.It needs further research to comprehensively consider multiple measurement factors and select the optimal ratio.Therefore,in this study,five fertilization treatments and one control were set under equal nitrogen conditions,and the proportion of organic fertilizer nitrogen replacing inorganic fertilizer nitrogen in fertilization treatment was 0,15%,30%,60%and 100%（no fertilizer、100U、15S+85U、30S+70U、60S+40U、100S）,respectively,to explore the winter wheat yield,nitrogen absorption and utilization,soil carbon sequestration effect,temporal and spatial changes of soil nitrogen,and greenhouse gas emission characteristics of farmland under different replacement ratios.Based on the above research content,this study aims to give consideration to yield and environmental benefits,so as to screen out the optimal proportion of organic and inorganic fertilizer application in Guanzhong area,and provide certain basis for the sustainable development of local agriculture.The main results of this study are as follows:（1）There were significant differences in the nitrogen accumulation amount in the ground part of wheat at maturity stage.The lowest nitrogen accumulation was found in no fertilization treatment.With the increase of organic fertilizer replacement ratio,the nitrogen accumulation of stem,leaf and ear increased first and then decreased.The nitrogen accumulation of ear in 30S+70U treatment was the highest,and the average increase was42.11%in two years compared with inorganic fertilizer alone.The accumulation of ¹⁵N in ear was higher than that in stem and leaf,and the accumulation of ¹⁵N in ear decreased with the increase of organic fertilizer replacement ratio.The crop yield under low organic fertilizer replacement ratio（15-30%）increased significantly compared with that without fertilizer,and the yield under 15S+85U treatment in the first year was higher,which increased 1736.22 kg/hm²（30.31%）,compared with that without fertilizer.In the second year,the yield of 30S+70U treatment was higher,which increased by 1455.61 kg/hm²（24.54%）compared with no fertilization.There was no significant difference in crop yield between total organic fertilizer and no fertilizer.（2）The combined application of organic and inorganic fertilizers significantly increased the content of soil particulate organic carbon（Particle Organic Carban POC）,and the POC content increased with the increase of the amount of organic fertilizer,but there was no significant difference between different treatments of mineral binding organic carbon（Mineral binding Organic Carbon MOC）.The increase of POC content led to the increase of soil organic carbon（SOC）.The SOC under 100S treatment was the highest among all treatments.The SOC under 100S treatment in the second wheat season increased by 15.39Mg/hm²（56.23%）compared with that without fertilization.The promotion effect of each treatment on organic carbon storage was as follows:high organic fertilizer replacement>low organic fertilizer replacement.Combined application of organic and inorganic fertilizers could effectively increase the total nitrogen content of 0-20cm soil.Low amount of organic fertilizer combined with inorganic fertilizer provided a higher level of NH₄⁺-N and NO₃-N contents for the whole wheat growth period.60S+40U treatment could effectively reduce the leaching loss of NH₄⁺-N in deep soil.The percentage of urea ¹⁵N and residue in the soil treated with 30S+70U were higher,indicating that the combined application of organic and inorganic fertilizer was beneficial to the retention of inorganic fertilizer nitrogen in the soil.（3）Among the three kinds of greenhouse gases,the cumulative emission of CO₂ was the highest,keeping at 1234.70-2121.01 kg·hm^-2·yr^-1;Combined application of organic and inorganic fertilizers increased the cumulative emissions of N₂O and CO₂,and the cumulative emissions of N₂O and CO₂ at 60S+40U increased by 0.90 and 89.21 kg·hm^-2·yr^-1,respectively,compared with 100U in the second wheat season.On the whole,there is no significant difference between the cumulative emissions of three kinds of greenhouse gases.In conclusion,the combined application of low amount organic and inorganic fertilizer can effectively promote the transfer of nitrogen to grain at the mature stage of wheat under the iso-nitrogen condition,and thus significantly improve the nitrogen utilization rate of wheat,and ultimately increase the crop yield.At the same time,the combination of organic and inorganic fertilizers can further reduce the leaching of available nitrogen into deep soil,and there is no significant difference in the cumulative emissions of greenhouse gases between the combination of organic and inorganic fertilizers and the single application of inorganic fertilizers.Therefore,under the premise of constant nitrogen application,the replacement of inorganic fertilizers by 15-30%organic fertilizers in Guanzhong area can reduce the application amount of inorganic nitrogen,giving consideration to the yield and ecological benefits.