Effects Of Biochar On Soybean Growth And Rhizosphere Soil Environment Under Different Water And Nitrogen Conditions

Soybeans are one of the traditional foods of Chinese dietary life,and improving soybean self-sufficiency is a step that cannot be ignored in the larger food perspective of food security.In order to increase soybean yields and improve quality,improve water and nutrient use efficiency while reducing soil and environmental pollution,and develop sustainable agriculture.Four graded levels of biochar treatments(B27:45t/hm~2,B18:30t/hm~2,B9:15t/hm~2,B0:0t/hm~2)were added to soybean trial plots in different soil types.By taking soybean inter-root soils at harvest time,soil environmental factor indicators were measured to determine the pattern of biochar effects on the physical and chemical properties of soybean inter-root soils,to monitor the pattern of changes in the growth status of biochar-treated soybeans throughout the reproductive period,to explain the effects of biochar on soybean growth and yield,and to investigate the factors contributing to the abundance and structure of diazotrophic microbial communities in biochar-modified soils.Different levels of irrigation(adequate irrigation W1,moderate deficit W2 and severe deficit W3),different levels of nitrogen application(N0:0kg/hm~2,N1:75 kg/hm~2and N2:150 kg/hm~2,respectively),and different levels of charcoal application(B0:0 t/hm~2,B1:15 t/hm~2and B2:A three-factor,three-level orthogonal experiment was conducted to determine the physical and chemical properties of soybean inter-root soil at harvest,and to analyse the effects of water and nitrogen coupled with biochar application on the physical and chemical properties of soybean inter-root soil,and to understand the growth pattern and yield and quality response of soybean under the coupled water,nitrogen and charcoal measures.The results of the study were used to screen out the optimal water,nitrogen and charcoal management combinations,providing a theoretical basis and technical support for reducing farming costs and promoting the development process of soybean in China.The main results achieved are as follows:(1)The application of different gradients of biochar in the bean field soil significantly affected the physicochemical properties of the soil,with the application of biochar decreasing the soil capacity and increasing the water content and p H.Under small mound soil conditions,the p H of biochar-treated soils increased but not significantly,but under red loam soil conditions,B27,B18 and B9 increased by 2.76%-15.62%compared to B0,improving soil acidification better.The organic carbon,fast-acting phosphorus and total nitrogen contents of the soil increased significantly in the biochar treatment,providing a large amount of nutrients to the soil.The ammonium nitrogen content was reduced and the nitrate nitrogen content did not change significantly.(2)The best yield was achieved in soybean field with 15/hm~2biochar treatment in group B9.The highest yield was achieved in group B9 treatment under small mound soil conditions,and both group B9 and B18 yielded more than the control group,increasing by 51.65%and10.28%respectively.There was no significant difference in seed yield between the B27treatment and the B0 treatment.There was no significant effect of biochar treatment on soybean quality.The pattern of effect of different levels of biochar application on soybean leaf area index in soybean fields was not significant,but it could be seen that the leaf area index of the biochar treatment group at pod stage was greater than that of the control group.(3)Compared to pure soil,biochar application reduced the diversity of nitrogen-fixing microorganisms in small mound soils but increased the abundance of nitrogen-fixing nif H genes,with the copy number of the treatment applying 45 t/hm~2biochar being four to six times higher than the copy number of the other three treatments.The addition of biochar altered the community structure of nitrogen-fixing microorganisms,with the microbial community remaining stable at smaller biochar application rates,but changing with increasing biochar application rates.In addition,biochar application reduced the proportion of its unique nitrogen-fixing bacteria,but did not affect the proportion of nitrogen-fixing bacteria common to biochar-amended soils versus pure soils.(4)In the three-way orthogonal test study of water,nitrogen and charcoal,the most significant factors affecting soil physicochemical properties were biochar,followed by water deficit,and finally nitrogen application level,and the other physicochemical properties increased to a certain extent with the decrease in the capacity of biochar addition.(5)In a three-factor,three-level orthogonal trial study of water,nitrogen and charcoal,the application of nitrogen fertiliser increased the height of soybean plants with the degree of irrigation deficit and,later in growth,with the application of nitrogen fertiliser.The water,nitrogen and charcoal treatments had a small effect on stem thickness and leaf area index in the early stages of soybean growth.During the peak growth period,deficit irrigation and nitrogen application had a significant effect on stem thickness and leaf area index,and in the later stages of growth,leaf drop and leaf area index decreased.(6)The main effects and interactions of water,nitrogen and charcoal had a significant effect on seed yield.The optimal combination of water,nitrogen and charcoal for soybean yield was W1N1B1,based on the orthogonal test and the analysis of the results.W3N2B1 treatment.The effect of irrigation deficit and nitrogen application on soybean seed oil content was highly significant,with seed oil content increasing with deficit and nitrogen application.