Study On The Mechanism Of Bacillus Subtilis To Improve The Salt Tolerance And Nitrogen Fertilizer Utilization Of Cotton In Saline Alkali Soil

Increased soil salinization and low nitrogen fertilizer utilization have become the main problems restricting the sustainable development of agriculture in Northwest China.Therefore,this paper adopts the "3414" experimental design plan,through a potting experiment of bacterial fertilizer and salt coupling with Xinjiang typical crop cotton as the research object,to study the influence of Bacillus subtilis on soil indicators and cotton physiological growth indicators in saline soil,and discuss The influence of Bacillus subtilis on nitrogen absorption,distribution and utilization was established.A ternary quadratic regression model was established based on experimental data to analyze the influence of the three factors of bacterial salt nitrogen on cotton yield,and proposed the Bacillus subtilis inoculant,salt,and nitrogen fertilizer The best combination plan for cotton growth in Xinjiang provides a certain reference for the combined application of bacterial fertilizers for cotton growth.The main conclusions are as follows:(1)The application of Bacillus subtilis could effectively improve soil water content and change the distribution of salt in root zone.The water content of soil profile first increased and then decreased with the application rate of bacteria;The water consumption of the treatment with fungicides was lower than that of the treatment without fungicides.Secondly,Bacillus subtilis played a positive role in promoting the transformation of nutrients such as nitrogen,phosphorus,and potassium in salinized soil,and played a certain role in nitrogen fixation,phosphorus release and potassium release.With the increase of application rate,soil available potassium and available phosphorus content increased first and then decreased.(2)The effect of Bacillus subtilis on cotton growth physiological indexes was significant.Under salt stress,the application of Bacillus subtilis could promote the growth of cotton plants in a certain range.Plant height,stem diameter and leaf area index increased first and then decreased with the increase of bacterial fertilizer application.Bacillus subtilis can increase the nitrogen uptake of each part of cotton to a certain extent.The final nitrogen content of each part of cotton organs is shown as bell>leaf>stem>root,and the bacterial fertilizer treatment has a greater promoting effect on the nitrogen uptake of cotton roots.Bacillus subtilis can alleviate oxidative damage under salt stress by improving leaf physiological activity and regulating leaf environment.Except for MDA,the physiological indexes of cotton were promoted by Bacillus subtilis,and the effect of Bacillus subtilis on proline was greater.Secondly,Bacillus subtilis is conducive to the efficient use of captured light energy for photosynthesis,increasing the utilization of light energy in leaves.The application of bacterial fertilizer improves the maximum photochemical efficiency(Fv/Fm)and photosynthetic performance index(Plabs)of PSII.(3)The yield and water use efficiency of cotton increased first and then decreased with the increase of bacterial application amount,and all treatments were higher than the bacterial fertilizer control treatment,with the yield increasing by 10.47%～43.13%and water use efficiency increasing by 13.37%～45.34%.(4)A regression model of bacterial salt-nitrogen coupling was established,and the regression equation was verified to be valid and can be used for yield prediction.The order of influence of each factor in the equation is as follows:nitrogen application amount>soil salinity>bacteria application amount.Through the double-effect analysis,it can be known that nitrogen bacteria and nitrogen salts are synergistic effects,and the synergistic effect of nitrogen bacteria>the synergistic effect of bacteria salt,and the antagonistic effect of salt bacteria.Bacillus subtilis has a more obvious promotion effect on cotton in mildly and moderately saline soil.Both the amount of bacteria applied and the yield of cotton showed a parabolic relationship,but with the increase of the amount of nitrogen fertilizer applied,the optimal amount of applied bacteria increased continuously.Through simulation calculation,the combination plan of bacterial fertilizer and salt at maximum yield is calculated.When the nitrogen application rate is 381.195 kg/hm2,the soil is mildly saline soil,and the bacteria application rate is 6 mg/kg,the cotton yield reaches the maximum.