Effects Of γ-polyglutamic Acid On Water And Salt Transport In Saline-alkali Soil And Cotton Growth

China has a large population,less land and scarce cultivated land resources.Improving saline-alkali land is of great significance for increasing cultivated land reserve resources and ensuring food security.y-Polyglutamic acid（γ-PGA）is an ’ environmentally friendly ’ polymer material.Because it contains a large number of carboxyl groups and amide groups,it has great potential in controlling saline-alkali soil and enhancing soil water holding capacity.In this paper,the response characteristics of water and salt transport characteristics and water redistribution toγ-PGA（0%,0.4%,0.6%,0.8%）in soils with different salinization degrees（mild salinization soil and moderate salinization soil）under the condition of water infiltration were studied by indoor soil column test.A pot experiment was conducted to study the effects of γ-PGA（0%,0.2%,0.4%,0.6%）on soil water and salt distribution and cotton growth in different saline-alkali soils（non-saline soil,mild saline-alkali soil,moderate saline-alkali soil）under different irrigation amounts（3600 m³/hm²,4500 m³/hm²,5400 m³/hm²）.The main research results are as follows:（1）The regulation effect of γ-PGA on soil water transport and water holding capacity under different salinization degrees was clarified.The application of γ-PGA in saline-alkali soil can reduce soil water infiltration capacity,increase soil water content and soil water holding capacity.Under the condition of ponding infiltration,with the increase of γ-PGA application amount,the cumulative infiltration amount of mild saline-alkali soil and moderate saline-alkali soil decreased by 17.8%-26.8%and 16.30%29.20%respectively compared with that of non-applied treatment.At the end of infiltration,the soil water content increased by 1.25%-4.62%and 1.83%-6.82%,respectively.During the water redistribution period,the soil water content increased by 0.30%-8.63%and 0.84%-8.54%,respectively.The water movement parameters of mild saline-alkali soil were more sensitive to the amount of γ-PGA application,and the water movement parameters of moderate saline-alkali soil were less sensitive to the amount of γ-PGA application.Under the condition of pot experiment,with the increase of γ-PGA application amount,the soil water content increased by 0.31%-16.44%compared with that without γ-PGA application during the seedling stage to flowering and boll stage of cotton growth.（2）The distribution characteristics of soil salinity and salt ions in different saline-alkali soils under different irrigation amounts and γ-PGA application amounts were clarified,and the regulation effect of γ-PGA on soil salinity was clarified.At the end of infiltration and during water redistribution:the application of γ-PGA in slightly saline-alkali soil reduced the soil salt content in 0-20 cm soil layer and increased the soil salt content at 30 cm at the bottom of soil layer.With the increase of γ-PGA application rate,the soil salt content at the bottom of the soil layer increased significantly.The soil salt content at the bottom of the soil layer treated with γ-PGA was 1.08-3.97 g/kg higher than that without treatment.Under the condition of pot experiment,the soil salt content of γ-PGA treatment increased in the early stage of cotton growth,but more salt was concentrated in the bottom layer of pot during the flowering and boll opening stage of cotton growth.The application of γ-PGA increased the amount of salt leaching from cotton seedling stage to boll opening stage,and the amount of salt leaching was the highest in 0.2%γ-PGA treatment in both saline-alkali soils.The contents of Na⁺,Ca²⁺and Mg²⁺in the 0-10 cm soil layer were lower than those in the untreated soil at the end of infiltration and during water redistribution.During the flowering and boll-opening stage of cotton growth,the content of salt ions in the shallow soil of cotton roots decreased.During the whole growth period of cotton,the application of γ-PGA increased the ratio of potassium to sodium in the soil,reduced the ratio of sodium adsorption and structural stability cation ratio in each soil layer during the bud stage to the opening stage of cotton.（3）The physiological response characteristics of cotton to different γ-PGA application and irrigation amount were revealed,and the effect of γ-PGA on cotton growth and yield was clarified.Under the condition of pot experiment,the plant height and leaf area index of cotton without treatment were the highest in the same period.The plant height and leaf area index of cotton treated with 0.4%γ-PGA were the smallest in the same period.In the rapid growth and development stage of cotton,the application of γ-PGA promoted the growth of cotton from bud stage to boll opening stage,increased the activity of antioxidant enzymes in cotton,especially the most significant effect on catalase,increased the plant height and leaf area index of cotton,and increased the yield and dry matter quality of cotton.The application of γ-PGA increased the water use efficiency of cotton,but under the premise of the same amount of γ-PGA,excessive irrigation not only led to the decrease of water use efficiency but also inhibited the early growth of cotton.（4）The regulation mechanism of γ-PGA on soil salinity and cotton yield was clarified,and the suitable application amount of γ-PGA with ideal improvement effect on saline-alkali land was proposed.By analyzing the correlation between the amount of γ-PGA applied and the various influencing factors,it was found that the amount of γ-PGA applied reduced the correlation coefficient of salt-yield,Mg²⁺-yield and Ca²⁺-yield,and increased the correlation degree of cotton leaf enzyme activity-yield.The indirect path coefficients of γ-PGA application amount with soil salt content,Na⁺and Mg²⁺content were all negative,and the indirect path coefficients with catalase,superoxide dismutase and irrigation amount were all greater than 0.The principal component analysis showed that the comprehensive score of 0.4%,0.6%γ-PGA treatment was higher in two different degrees of salinization soil.（5）The cotton growth model under the condition of applying γ-PGA was constructed,and the optimization scheme of γ-PGA application amount and irrigation amount in different degrees of saline-alkali soil considering production cost was proposed.The combined optimization model based on Logistic model and Richards model can accurately estimate the plant height of cotton under different degrees of salinization soil and different γ-PGA application amounts.By establishing the multiple regression equation of γ-PGA application amount-soil salt content-irrigation water amount,the application of γ-PGA can increase cotton yield under salt stress and deficit irrigation conditions.The multi-objective fuzzy optimization model showed that the comprehensive benefit of 0.2%γ-PGA treatment,4500m³/hm² irrigation treatment in non-saline-alkali soil,0%γ-PGA treatment,4500m³/hm² irrigation treatment in mild saline-alkali soil,0.2%γ-PGA treatment and 5400m³/hm² irrigation treatment in moderate saline-alkali soil was the highest.