Soil And Crop Yield Effects Of Winter Wheat-Alfalfa Intercropping System

Intercropping,as a diversified planting mode,can make more rational and efficient use of water resources,improve the nutrient accumulation in the soil caused by excessive fertilization,and improve the efficiency of soil water and nutrient utilization.During the whole growing period,wheat-alfalfa intercropping not only harvest wheat,alleviate the contradiction between the growing food demand and the limited land resources,but also increase the forage,and enrich the output of crops in the farmland.In general,it promotes the development of animal husbandry,improves people’s dietary habits,and ensures the common development of resources,ecological environment and economic benefits.The purpose of this study is to clarify the changing laws of soil moisture,nutrient content,crop yield and nutrient absorption efficiency under different planting modes through field experiments,so as to provide theoretical basis and feasible suggestions for the research of intercropping system of grain and grass and the development of green agricultural production in the new era.In this study,field experiments were conducted in Dongdu village,southwest of Shanxi Province.Wheat and alfalfa were selected as the research objects,and three planting modes were established:Wheat monoculture,alfalfa monoculture and wheat-alfalfa intercropping.Through the combination of field observation and indoor analysis,SPSS and other software were used to analyze soil water and nutrient,crop yield and nutrient absorption efficiency,and interspecific competitiveness of crops under different planting modes.The results are as follows:（1）In terms of the soil moisture,no matter which planting mode,the soil moisture content in the period of wheat returning to green and fallow was higher than that in the wheat harvest period,the soil moisture content in turn was wheat monoculture>wheat-alfalfa intercropping>alfalfa monoculture,and the water consumption in the symbiosis period of Wheat and alfalfa was higher than that in the fallow period of wheat.The water use efficiency of intercropping system was 19.81%～28.28%higher than that of wheat monoculture,20.37%～63.28%higher than that of alfalfa monoculture,and the water equivalent ratio was 1.31～1.71,indicating that wheat-alfalfa intercropping has significant water advantage.（2）In terms of soil nutrients,after Intercropping of wheat and alfalfa,alfalfa and wheat roots formed a nutrient concentration area in the soil,which became the main source of nutrients for crops.In the symbiosis period of wheat and alfalfa,the content of soil organic matter increased after intercropping because of the growth of alfalfa,and decreased significantly after the whole growth period.There was a close relationship between soil nitrogen and organic matter content in the soil profile.In the early stage of wheat alfalfa growth,the nitrogen content in the 0-60cm layer of soil in the intercropping system decreased significantly due to the competition between alfalfa and wheat.As the nitrogen consumption increased gradually after the growth of wheat alfalfa,the rhizosphere soil gradually entered the stage of nitrogen deficiency.After the fallow of wheat field,the soil nitrogen was restored.At this time,the nitrate nitrogen in the soil was accumulated in the deep soil along with the vertical leaching of its profile.After intercropping,the risk of nitrogen leaching in the soil profile was avoided due to the continuous growth of alfalfa,and the utilization rate of nitrogen was improved.The phosphorus content in 0-100cm layer soil decreased significantly due to the growth of alfalfa.After intercropping,not only slowed down the consumption of phosphorus,but also increased the phosphorus activity of the soil around the rhizosphere.In the agricultural production process,it was still necessary to apply phosphorus fertilizer to ensure the normal growth of crops.Alfalfa growth also consumed 0-60cm layer of soil potassium content.Intercropping to a certain extent alleviated the crop’s consumption of potassium,and reduced the 60-200cm layer of soil potassium content.Potassium fertilizer still needs to be applied in production practice.（3）In terms of the nutrient content and absorption efficiency of crops,wheat-alfalfa intercropping not only increased the nitrogen content of wheat plants（grain and stem leaf）,but also increased the phosphorus content of wheat stem leaf.The nitrogen content of wheat stem leaf in intercropping increased by 8.0%～12.5%,the phosphorus content increased by14.3%～35.7%and the grain nitrogen content increased by 8.5%～14.0%compared with wheat monoculture.Compared with wheat monoculture,the nitrogen accumulation of intercropping system increased by 10.7%～17.4%;Compared with alfalfa monoculture,the nitrogen accumulation of intercropping system increased by 32.8%～74.3%,the phosphorus accumulation increased by 34.4%～76.3%,and the potassium accumulation increased by40.7%～74.4%.The nitrogen absorption efficiency of intercropping system was increased by10.8%～17.2%than that of wheat monoculture and 20.0%～49.5%than that of alfalfa monoculture.The phosphorus and potassium absorption efficiency of intercropping system was increased by 33.3%～76.5%and 40.8%～74.6%respectively.Therefore,wheat-alfalfa intercropping was beneficial to the improvement of plant nutrient content and absorption efficiency.（4）In terms of crop yield,wheat-alfalfa intercropping reduced the grain yield by 19.68%～46.50%,biomass by 28.32%～38.76%and alfalfa biomass by 13.64%～19.27%compared with monoculture due to the competitive effect of two crops on soil water and nutrient resources.However,the yield of wheat-alfalfa intercropping system was significantly increased by 14.64%～32.14%compared with wheat monoculture,and 21.13%～63.60%compared with alfalfa monoculture,which realized the system crop yield advantage and provided theoretical basis for intercropping production practice.（5）From the perspective of interspecific competitiveness,the net yield of wheat-alfalfa intercropping crops was 1710.39～4251.19 kg·hm^-2,and the land equivalent ratio was 1.34～1.67,which had significant intercropping advantages.In the intercropping system,the Aaw of alfalfa to wheat was-0.55～（-1.33）and less than 0,and the CRaw was 0.49～0.68 and less than 1.It shows that with the intervention of alfalfa planting years and human management measures,the competition of alfalfa is gradually weakened,and wheat still has yield advantage in intercropping.Therefore,winter wheat-alfalfa intercropping improved soil fertility,increased crop output,developed animal husbandry,changed agricultural structure,and met the needs of human food in the new era.