The soil infiltration test was carried out under the main forest types (Robinia pseudoacacia Linn.

Pinus tabulaeformis Carr.

Robinia pseudoacacia×Pinus tabulaeformis mixed forest

and Populus davidiana and Pinus communis natural secondary forest) in the gully region of the Loess Plateau by the double-ring infiltration method

and the soils were analyzed for physical and chemical characteristics to analyze their influence on the process of soil infiltration. The results showed that: (1) There were certain differences in soil physical and chemical characteristics of different forest types in the study area

and the soil physical and chemical properties of the natural secondary forest of Populus davidiana and Pinus communis were generally the best. The mixed forest of Robinia pseudoacacia×Pinus tabulaeformis was better than that of Robinia pseudoacacia Linn. and Pinus tabulaeformis Carr.; (2) Within the test period of 0~90 min

the soil infiltration rate of different forest types showed a rapid decrease (0~5 min) and a gradual decrease (5~60 min) over time

and the process of stabilization (60~90 min); the initial soil infiltration rate

stable infiltration rate and average infiltration rate of the four forests in descending order were as follows: Populus davidiana and Pinus communis natural secondary forests

Robinia pseudoacacia×Pinus tabulaeformis mixed forest

Robinia pseudoacacia Linn.

and Pinus tabulaeformis Carr.; (3) Among the four common soil infiltration models (Kostiakov model

Horton model

Philip model and general empirical model)

the general empirical model had the best fit for the soil infiltration process under different forest types in the study area

the fitting accuracy was above 0.990; (4) Correlation analysis results showed that the soil infiltration indices under different forest types were significantly negatively correlated with soil bulk density (P<0.01)

and were positively related to non-capillary porosity

> 0.25 mm water-stable aggregate content

sand content and the organic matter content (P<0.01); through path analysis and calculation of the determination coefficient of the main influencing factors

the results showed that the factor that had the greatest influence on the initial soil infiltration rate was the soil bulk density (0.309). The factor that had the greatest influence on the stable soil infiltration rate was > 0.25 mm water-stable aggregate content (0.251)

and the factor that had the greatest influence on the average soil infiltration rate was organic matter (0.408). These research results could provide a certain reference for the selection of tree species and the evaluation of soil and water conservation functions in the study area to build soil and water conservation forests.