Background Domestic and foreign scholars have conducted a lot of researches on the selection and adaptability of reclaimed vegetation, infiltration characteristics and hydrological effects of reclaimed mine soil, water-holding capacity of soil, and the restoration of soil fertility in the dump. However, it is lack of study on the saturated hydraulic conductivity of reclaimed soil with different reclaimed vegetations in the dump. The saturated hydraulic conductivity of reclaimed soil has an important impact on the formation of surface runoff and soil erosion in the dump, and it is of great significance to understand the soil water movement and the characteristics water leakage in this area. At present, there are many methods for determining the soil saturated hydraulic conductivity of a dump, but the accuracy of the measurement results needs to be improved.

Methods In the present study, saturated hydraulic conductivity of surface soil with 3 types of reclaimed vegetations (Robinia pseudoacacia forest land, Ulmus pumila forest land, and weeds) was measured and calculated by indoor-ring infiltration method, double-ring infiltration method and Hood infiltrometer, and 3 samples of every forests sample plot were taken. The soil water content, bulk density, porosity and gravel content were measured indoor and their effects on saturated hydraulic conductivity were analyzed. Saturated soil hydraulic conductivity of surface soil in the reclaimed soil was evaluated by analytic hierarchy process. The differences and its reasons of the results by indoor-ring infiltration method and double-ring infiltration method were clarified, and the optimal method of saturated water conductivity was discussed.

Results 1) Soil moisture content with different reclaimed vegetations was 13.51%-15.48%, and soil bulk density was R. pseudoacacia forest land > weeds > U. pumila forest land. The soil organic matter was 6.17-8.05 g/kg. The gravel content of R. pseudoacacia forest land, U. pumila forest land and weeds were 52.39%, 47.52%, and 54.03%, respectively. The sand content of three reclaimed vegetations was 36.80%-41.43%, silt content was 48.87%-54.27%, and clay content was 8.30%-9.70%. 2) The soil saturated hydraulic conductivity increased significantly with the increasing reclamation years, which was due to the improvement of soil structure by vegetation restoration. The surface soil saturated hydraulic conductivity of R. pseudoacacia forest land, U. pumila forest land, and weeds were 0.77, 0.54, 0.48 mm/min, respectively, and there was no significant difference among three reclaimed vegetations (P>0.05). 3) The results of different measurement methods were Hood infiltrometer < double-ring infiltration method < indoor-ring infiltration method, and the accuracy of Hood infiltrometer was the highest. 4) The saturated hydraulic conductivity was a significant positive correlation with gravel content and silt content, and was a significant negative correlation with bulk density and clay content. The water conductivity of surface soil in the dump was U. pumila forest land (0.523) > R. pseudoacacia forest land (0.501) > weeds (0.488).

Conclusions The soil saturated hydraulic conductivity is shown as follows U. pumila forest land > R. pseudoacacia forest land > weeds. The results of soil saturated hydraulic conductivity measured by the three methods differed. The dispersion degree and error of the results measured by Hood infiltrator are less than those measured by indoor-ring infiltration method and double-ring infiltration method, there is no need to disturb soil and no head pressure, which is more in line with the actual process of soil water infiltration. Hood infiltrometer shows better applicability in measuring surface soil saturated hydraulic conductivity.