Based On ¹⁵N Isotope Technology,the Effect Of Re-seeding Green Fertilizer After Wheat Reduced Fertilizer Application Was Studied

In this study,taking the decomposition of leguminous green manure Viciavillosa L.as the starting point,using the ¹⁵N isotope tracing technique combined with the long-term localization experiment of reduced chemical fertilizer,in order to clarify the effect of long-term planting of Vicia villosa L.on soil fertility and wheat yield of post-stubble crops in the cold and cool areas of Qinghai Plateau,to understand the accumulation and distribution of nitrogen from different sources of nitrogen,to elucidate the important role of green manure in agricultural production in Qinghai Plateau,and to explore the connection between planting Andyros Vicia villosa L.and the uptake and utilization of soil nitrogen reservoir and nitrogen,The mechanism of fertilization and improvement of soil ecological environment was revealed,to optimizing the allocation mechanism and utilization strategy of resources in agricultural ecosystems.（1）In order to clarify the decomposition characteristics of Vicia villosa L.and the nutrients release laws of nitrogen,phosphorus and potassium were studied with nylon mesh bags in the field.The results showed that the decomposition rate of green manure of dry matter was 38%within 50 days after being turned over,and the decomposition rate was slow at the later stage.After sampling,the cumulative decomposition rate was 86.39%.In the whole decomposition process,the release rate all ranked as N>P>K,showed the same trend,and the release rate of N and K was56.54%and 74.27%in 52 days,respectively,while the release rate was slow in the later stage.At the end of decomposition,the cumulative decomposition rate of nutrients reached 91.31%and 99.04%.The release rate of phosphorus is slow and fluctuating,and the content of phosphorus increases during the decomposition period.After sampling,the cumulative decomposition rate is 75.71%.The relationship between dry matter cumulative decomposition rate,nutrient cumulative release rate and decomposition time can be fitted by linear function and logarithmic function.Through this experiment,it is predicted that replanting green manuret can provide172.80 kghm^-2 of pure nitrogen,10.93 kghm^-2 of pure phosphorus and 139.63 kghm^-2of pure potassium for the following crops.（2）In the soil-plant system,the performance of the nitrogen from chemicalfertilizer was ranked as plant uptake and utilization>residues in the soil>losses.The fate of nitrogen from green manure was as follows:residues in the soil>losses>plant uptake and utilization.The uptake of nitrogen from chemical fertilizer by wheat was greater than that of nitrogen from green manure.The uptake of nitrogen from chemical fertilizer by wheat was in the range of 46.00～54.08%,while the uptake of nitrogen from green manure was 20.71～28.21%.The combined application of chemical fertilizer and green manure can increase the uptake of nitrogen by wheat from both sources.The residue of nitrogen from green manure in the soil（38.47～58.22%）was greater than that of nitrogen from chemical fertilizer（31.44～40.69%）;the loss of nitrogen from green manure（21.07～33.31%）was also more significant than that of nitrogen from chemical fertilizer（5.22～22.56%）.At the mature stage of wheat,the distribution of nitrogen from both sources in different organs was ranked as grain>glume>leaf>stem>root.The combined application had a significant（p<0.05）effect on nitrogen accumulation in the grains,with an increase in nitrogen accumulation of 10.14～59.77%.The combined application of green manure and chemical fertilizer could significantly raise dry matter accumulation in various wheat organs at different growth stages,with an increase of 8.70～51.9%.This strategy could also facilitate the accumulation of nitrogen in the reproductive organs of wheat.（3）Using Qingchun No.38 wheat and Turkmen hairy Vicia villosa L.as testmaterials,different proportions of chemical fertilizers were reduced under the condition of quantitative pressure of green manure,and the changes of nutrient accumulation and distribution ratio and fertilizer utilization rate of different organs in different growth periods of wheat were analyzed.The results showed that the dry matter accumulation and nutrient accumulation of wheat at each growth stage were significantly increased by the application of nitrogen 157.50 kg.hm^-2 and phosphorus78.75kg.hm^-2 with the treatment of turning green manure,and the transfer efficiency of nitrogen,phosphorus and potassium to reproductive organs was 0.91,0.92 and 0.71,respectively,and the absorption and utilization efficiency of nitrogen and phosphorus in wheat plants was 0.48 and 0.11,respectively.Therefore,the pressure of green manure hairy leaf Vicia villosa L.was 30000kg.hm^-2,the nitrogen application was157.50kg.hm^-2,and the phosphorus was 78.75kg.hm^-2,which was conducive to improving the dry matter accumulation and nutrient absorption and utilization efficiency of spring wheat in Qinghai Plateau,and under this condition,the yield unified with environmental,economic and ecological benefits could be obtained,which was 3.95%and 43.40%higher than that of conventional fertilization and control,respectively.Overall,in the wheat-green manure hairy leaf Vicia villosa L.plantingsystem,it can be seen from the positioning test of turning green manure that the over-pressed green manure replaces 30%of the chemical fertilizer,that is,the green manure turnover is 30000kg.hm^-2,the nitrogen content is 157.50kg.hm^-2,the phosphorus content is 78.75kg.hm^-2,the wheat yield is the highest,the plant has a high efficiency of nutrient absorption and utilization,and the distribution ratio of nitrogen in various organs can be optimized under this condition,and the nutrient transfer to the reproductive organs can be regulated.It is conducive to coordinating the source-reservoir relationship between soil and plants,and at the same time,the green mantle leaf Vicia villosa L.is decomposed in the soil system after rolling,which can provide pure nitrogen 172.80kg.hm^-2,pure phosphorus 10.93kg.hm^-2,pure potassium 139.63kg.hm^-2 to the stubble crop plot.In addition,the absorption of nitrogen from fertilizer sources by wheat was between 46.00 and 54.08%,and the absorption of nitrogen from green manure sources by wheat plants was between 20.71and 28.21%,and theoretically,the nitrogen absorbed by wheat was 72.45 to 85.18kg.hm^-2,there are 35.79～48.75 kg.hm^-2 green manure nitrogen for wheat absorption and utilization,in production,some of the nutrients required by crops during the growth period can be provided by the nutrients released after the decomposition of green manure hairy leaf Vicia villosa L.,thereby,the recycling of the soil nutrient bank can reduce the demand for fertilizer in the next season,and can effectively play the function of green mangoyle Vicia villosa L.weight loss and efficiency and fertilization soil.