Effect of thickness of gravel cover on infiltration process of tidal soil and its model optimization

Background  As an important agricultural soil in China, tidal soil is widely distributed in the Huang-Huai-Hai plain, and also in the middle and lower reaches of the Yangtze River. Due to unscientific human production activities in recent years, soil fertility is reduced and soil and water are easily lost. Here we aim to explore an effective method of improving the current situation of soil and water loss in tidal soil area.

Methods  S-shaped sampling was adopted. Based on an indoor one-dimensional vertical constant head infiltration experiment, the variation of tidal soil water infiltration process under gravel coverage (0, 3, 6, 9 and 12cm) was studied. The migration distance between the Mahalanobis reading and the wetting front of the soil column was recorded. Correlation analysis and variance analysis were carried out on the data, and 3 models of Philip, Kostiakov and exponential model were used to simulate the infiltration process of tidal soil.

Results  Gravel cover led to the significant increase in the migration distance of the wetting fronts (P < 0.05). In the same period, the cumulative infiltration of each treatments were higher than that of the control group (P < 0.05), The migration distance of the wetting fronts and cumulative infiltration capacity of the tidal soil can all be described by power function with the thickness of gravel cover, and the coefficient of determination was successively 0.995 as well as 0.983. The gravel cover changed the water infiltration curve of the tidal soil, and increased the initial infiltration rate, stable infiltration rate and average infiltration rate. When the thickness of gravel cover exceeded 9cm, the stable infiltration time of the tidal soil increased significantly (P < 0.01). The initial infiltration rate, stable infiltration rate and average infiltration rate of tidal soil were all positively correlated with the thickness of gravel cover.

Conclusions  Gravel cover can promote moisture infiltration of tidal soil and Kostiakov infiltration model has the best fitting effect on the results of tidal soil infiltration, which made it suitable to analyze and predict the tidal soil infiltration process under gravel cover.