Background The black soil area in Northeast China is an important grain producing area in China. The problem of soil degradation caused by soil erosion in the black soil area is becoming more and more obvious. It is of great significance to study the infiltration characteristics of black soil with different degrees of erosion to control slope soil erosion.The application of HYDRUS-1D model is more extensive, and it is mostly concentrated in the arid area of Northwest China.Whether the model can simulate the infiltration of black soil needs further study or not.

Methods The author collected black soil samples with slight, moderate and severe eroded degrees in the typical black soil area of Heshan Farm in Heilongjiang province, and determined the one-dimensional vertical infiltration process based on indoor soil column experiments. The black soil with different eroded degrees was determined according to the thickness of the black soil layer (layer A) and the thickness of the deposited layer (layer B). The HYDRUS-1D model was used to simulate soil infiltration. The simulation results were compared with the measured data, and the applicability of the model in the black soil area was evaluated by using Origin software.

Results 1) Firstly, the stable infiltration time of severe, moderate and slight eroded soil was 8, 26 and 36 h, respectively, and the infiltration rate was 0.72, 0.25 and 0.16 cm/h, respectively. The higher the degree of erosion, the greater the cumulative infiltration amount of soil in the same infiltration duration. 2) Secondly, in terms of the change characteristics of the wetting front with time, the soil with slight, moderate and severe eroded degrees has a slower infiltration rate to the lower layer, and the wetting front migration rate slows down accordingly, and the average speed of the wetting front migration of the soil with three erosion degrees is: 2.52, 3.32 and 9.85 cm/h, respectively. 3) Finally, there are some differences in the trend of soil moisture content with time in the infiltration process of the three soils. The saturated water content of soil decreases with the increase of erosion degree. The saturated water content of slight eroded soil is about 4.9 % higher than that of moderate eroded soil, and the saturated water content of specific severe eroded soil is about 9.4 % higher than that of moderate eroded soil. The saturated water content of each soil decreased with the deepening of soil layers. According to the erosion intensity from weak to strong, the saturated water content of the surface soil was 7.8 %, 8.0 % and 12.8 % higher than that of the lowest layer, respectively.

Conclusions The infiltration process simulated by HYDRUS-1D underestimates the infiltration of soil with high sand content and overestimates the infiltration of soil with high clay content. The infiltration capacity of slight and moderate eroded soil was overestimated, while the infiltration capacity of severe eroded soil was underestimated. Among them, the fitting results of moderate eroded soil infiltration are better than those of the other two erosded soils. We can try to further modify the parameter values of residual water content and saturated water content, and optimize the fitting results.