Abstract:Coastal saline-alkali land is an important land reserve resource, as well as an important way to ease the pressure on agricultural land. Soil amendments are widely used in soil improvement. Grasping its effect on water movement and salt transport is the first problem for amendment application. In order to explore the effects of humic acid on soil water movement and salt transport characteristics and infiltration parameters, one-dimensional vertical infiltration experiments were performed at five application rates (0, 1, 3, 5, 7 g/kg). The results showed that when the infiltration time was same, the cumulative infiltration amount and wetting front of each treatment decreased with the increase of humic acid application; for the same infiltration depth, the infiltration time required with the increase of humic acid application, cumulative infiltration and average water content in the profile increased significantly. Compared with CK, the cumulative infiltration and water contents increased by 8.0% and 10.0% respectively when the application rate was 7 g/kg when infiltration finished; the application of humic acid could promote the migration of salt from the soil profile to the deep soil layer and effectively reduce soil pH, compared with the CK application rate of 7 g/kg, the average desalination rate of 0—20 cm increased by 10.2%. The results showed that Philip and algebraic models could better describe the characteristics of water infiltration under the condition of humic acid application. The permeability (S) decreased with the increase of the amount of humic acid applied, and the overall shape coefficient α increased with the increase of the amount. Between the model parameters and the amount of humic acid had a follow linear relationship. In addition, the root mean square error and the average absolute error were 0.005~0.018, 0.004~0.014 cm3/cm3, indicating that the algebraic models could better describe the distribution of water content. The above research results provide a certain reference for the application of amendment in the improvement of coastal saline-alkali land.