Objective  This paper aims to explore the influence of structure and quantity of macropores with different diameter classes on the saturated hydraulic conductivity of soil, and to provide a theoretical reference for the study of soil water solute transport law, soil erosion control and soil pollution control in this area.

  Method  The study was carried out on water conservation forest in Wuzuoshan Forest Farm of Miyun Reservoir in Beijing suburb. Based on the industrial CT scanning technology, the three-dimensional spatial structure of soil macropores in the soil column was reconstructed to explore the influence of structural parameter density and quantity density of macropores with different diameter classes on the soil saturated hydraulic conductivity.

  Result  (1) Excepting for equivalent diameter large than 4.30 mm, the larger the equivalent diameter of macropores was, the smaller the quantity density and structural parameter density of macropores were. (2) In three soil layers of six sample plots, the proportion of macropores with an equivalent diameter of 0.31−2.30 mm to all macropores was higher than 95%. (3) The maximum saturated hydraulic conductivity of sample plot 1, 2, 5 and 6 was in 0−10 cm soil layer, and it decreased with the increase of soil depth, but except for sample plot 6. The saturated hydraulic conductivity of sample plot 4 increased with the soil depth increasing. (4) Except for the volume density of macropores with an equivalent diameter greater than 4.30 mm, all the other eigenvalue densities of macropores had a significantly positive correlation with the saturated hydraulic conductivity.

  Conclusion  (1) In the 0−30 cm soil layer, the saturated hydraulic conductivity of most sample plots decreases with the soil depth increasing, but it possibly increases with the soil depth increasing. (2) The equivalent diameter of macropores in the soil of forest is mainly concentrated in 0.31−2.30 mm, and its occupancy rate is more than 95%. (3) When equivalent diameter of macropores is smaller, the density of characteristic parameter of macropore structure is greater except for the volume and surface area of macropores. (4) There is a significantly positive correlation between the characteristic parameter of macropores and the saturated hydraulic conductivity except for the volume density of macropores with equivalent diameter greater than 4.30 mm. The influence of macropore number on saturated hydraulic conductivity is significantly greater than structure parameters of macropores.