Study On The Improvement Mechanism Of Fulvic Acid Application Rate On Saline-alkali Soil

Object:Soil salinization is the main obstacle to land resource utilization,which threatens land sustainable utilization,reduces agricultural productivity and directly causes farmers economic losses.Maintaining and steadily improving the soil fertility and productivity of farmland is an important link to improve the yield of cash crops.As a green and efficient organic amendment,fulvic acid combines soil improvement and plant growth regulation.At present,the improvement mechanism and effect of fulvic acid on Xinjiang saline-alkali soil need to be further explored.Methods:In 2021 and 2022,field tests were carried out in the 4th Company of the 51st Regiment in Tumshuk City,Xinjiang.Four application levels of fulvic acid were set:T1:150 kg·hm^-2,T2:300 kg·hm^-2,T3:450kg·hm^-2,T4:600 kg·hm^-2,CK was treated without fulvic acid as control.Results:Based on two years of field experiments,the changes of soil structure,physicochemical properties and humus degree under different application amounts of fulvic acid,as well as the response analysis of cotton growth,yield and quality to the improvement effect of saline-alkali soil were investigated,and the optimal application amount of fulvic acid in saline-alkali soil was determined,providing theoretical basis for the rational utilization and treatment of Xinjiang saline-alkali soil.The results of the study are as follows（1）After two years of improvement experiment,fulvic acid can significantly increase the content of soil hydrostable aggregates（p<0.05）,increase the large aggregates,mean mass diameter and geometric mean diameter,and reduce the fractal dimension of soil,which is conducive to the promotion and stability of soil structure.With the increase of the amount of fulvic acid applied,the effect on the soil structure showed a trend of first increasing and then decreasing.The effect was best when the application amount was 600 kg·hm^-2,but the difference was not significant compared with 450 kg·hm^-2（p>0.05）.（2）Fulvic acid can retain water and fertilizer,desalinate and reduce alkali.After two years of improvement experiment,compared with the control,the average soil moisture of 0～60 cm section increased by 6.16%-15.68%,the salinity decreased by 10.36%～25.63%,and the p H value decreased by 0.07～0.24,respectively.The profile content of soil organic matter was 0～20>20～40>40～60 cm.The effect on soil organic matter content first increased and then decreased with the increase of the application amount,but the difference was not significant compared with 450 kg·hm^-2（p>0.05）,and reached the maximum at 450kg·hm^-2,which increased by 27.46%compared with the control.（3）The contents of each component of soil humus in the profile of saline-alkali soil were0～20>20～40>40～60 cm,and the humin content in the same soil layer accounted for the highest proportion,while the contents of water-soluble substance and water-floating substance accounted for the lowest proportion.The application of fulvic acid significantly increased the ratio of humic acid to fulvic acid（CHA/CFA）and the ratio of humic acid to the sum of humic acid and fulvic acid（PQ value）in 0～20 cm soil（p<0.05）by 8.17～15.80%and 5.23～9.78%compared with the control,respectively.With the increase of fulvic acid application amount,the contents of humic acid and humin,humic acid and fulvic acid increased first and then tended to be stable.（4）When the application rate of fulvic acid was 600 kg·hm^-2,plant height,stem diameter,leaf area index,above-ground dry matter accumulation,seed cotton yield and fiber quality of cotton reached the maximum values under all treatments,but the difference was not significant compared with 450 kg·hm^-2（p>0.05）.In2022,compared with the control,the seed cotton yield increased by 11.09%under 450 kg·hm^-2 treatment.The yield composition was analyzed,and the increase was mainly due to the increase of boll number and boll weight per plant.（5）The correlation analysis between soil indexes and cotton growth showed that the yield of seed cotton had extremely significant or significant levels with soil aggregate,water content,salt content,p H,organic matter content and humification degree（p<0.05）.The yield of seed cotton was positively correlated with aggregate,water content,organic matter content and soil humus（p<0.05）,and negatively correlated with soil salinity and p H value（p<0.05）.Conclusion:The application of fulvic acid to saline-alkali soil improved soil structure and physical and chemical properties,enhanced soil humification,soil quality and soil fertility,and cotton growth positively responded to the effect of fulvic acid to improve saline-alkali soil.