| In order to solve the problems of high soil salinity,insufficient water holding capacity,and salt leaching difficulties in the Yellow River Delta,experimental and theoretical studies on the application of humic acid to improve clayey saline soils were conducted.The method of combining laboratory test and field test was used to design the soil moisture characteristic curve determination experiment,soil saturation hydraulic conductivity measurement and field soil profile water and salt change determination experiment under different humic acid addition amounts.The humic acid was clarified.It affects the soil water characteristic curve,water constant,and soil saturation hydraulic conductivity,and explores the action mechanism of humic acid to improve the moisture characteristics of clayey saline soil.The main research conclusions are as follows:(1)By using Gardner equation,exponential empirical equation and Rational equation to fit the measured data of soil water content,it is found that the fitting effect of Rational equation is higher than that of the other two equations,the relative error between the fitting value and the measured value under each treatment is less than 2%,the correlation coefficient R~2 is 0.9976,the maximum value is 0.9999,the root mean square error is under 0.5 and the fitting effect is better.(2)The soil moisture characteristic curve at 1 bar and 3 bar changes with the increase of the proportion of humic acid.The soil moisture content is the smallest under the CK treatment,the largest under the T8 treatment and increased by 80.26%and 51.42%compared with CK treatment.The difference is extremely significant(P<0.01).(3)After the application of humic acid,the soil water suction of each treatment was changed under the same water content.When the soil water content is CK,the soil saturated water content,capillary water holding capacity,and field water holding capacity are significantly improved.Among them,the soil water suction is under the CK treatment.Compared with CK,they have increased by 17.50%,116.50%,58.38%,158.38%,192.13%,229.13%,216.50%and 341.75%,among which the relative change in T1 is the smallest,the relative change in T8 is the largest,and the difference is extremely significant(P<0.01),Each water constant increases with the increase of the proportion of humic acid,and the change law is consistent with the change of soil water suction.(4)The soil saturated hydraulic conductivity changed significantly with the increase of the humic acid ratio.The soil saturated hydraulic conductivity increased by 5.59%,36.96%,8.59%,8.70%,and 59.52%compared with CK under T1~T8 treatment,respectively,73.29%of which the saturated hydraulic conductivity of T2,T5,T7,and T8 treatments increased by36.96%,59.52%,73.29%,and 128.05%,respectively,compared with CK,and the differences were extremely significant(P<0.01).Studies have shown that an appropriate amount of humic acid can increase soil saturated hydraulic conductivity and promote water infiltration and salt leaching of clay soil.(5)The ratio of the amount of humic acid added to the saturated hydraulic conductivity has a significant power function relationship with the increase of the humic acid ratio.The increase in the amount of humic acid increases the saturated hydraulic conductivity of the soil,which is conducive to soil salt leaching.(6)Humic acid can effectively increase soil water content and reduce soil salt content.By analyzing the changes of soil profile moisture in the spring of 2016 and 2017,it can be seen that the soil moisture content changes with the increase of soil depth and then increases first and then decreases,and the soil moisture content after humic acid is applied to the surface soil of 0~20 cm The amount of water changes significantly.Among them,in the soil of 0~20cm in spring of 2016,the soil moisture content increased first,then decreased and then increased with the increase of the humic acid ratio T1,T2,and T4 treatments increased by15.36,8.59%and 5.11%compared with CK,the changes were significant(P<0.05).By analyzing the changes of salinity in the soil profile in the spring of 2016 and 2017,we can see that the soil salinity changes with the depth of the soil layer,and then it increases first and then decreases.With the increase of the proportion of humic acid,it showed a trend of first decrease,then increase and decrease.Compared with CK treatment,T1,T2,T3 and T4treatments reduced the soil salt content by 26.10%,31.79%,20.43%and 23.64%,the salt reduction effect is obvious,and the difference is extremely significant(P<0.01).Based on the above studies,it has been shown that the soil moisture characteristic curve,water constant and soil saturated hydraulic conductivity have changed significantly by applying humic acid to improve the clay soil.The increase of soil water content and the decrease of soil salinity significantly occur.Based on the analysis results of indoor and field experiments,the optimal application amount of humic acid in the field is 0.12 kg/m~2. |
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