Test material
The test soil samples include HS, which has not been disturbed by human activities, and W-RS with a high humus content. These were taken from the surface layer of a mountainous area in the Guishui River Basin (see Fig. 1). The soil particle size (SPS) was measured using a Malvern 2000 laser particle size analyzer (Master-sizer Instruments Ltd., UK). The organic matter content (OMC) was measured via oxidation with a potassium dichromate solution (K2Cr2O7) in the presence of concentrated sulfuric acid (H2SO4). The soil total nitrogen (TN) and total phosphorus (TP) were measured with a UPG-722 ultraviolet spectrophotometer (Beijing Upu Technology Co., Ltd., China). Soil pH was measured with an MIK-PH6.0 meter (Hangzhou Asmik Sensing Technology Co., Ltd., China). The soil bulk density (SBD) was measured (Erbach, 1987) using the oven dry method, whereby an intact sample ring (UMS No. 006895, volume 250 ml, inner diameter 80 mm, height 50 mm) is placed into an oven and dried for 24 h at 105°C. The soil saturated hydraulic conductivity (Ks) was measured with a UMS KSAT device (Metergroup, Inc., USA) based on the German standards DIN 19683-9 and DIN 18130-1 and using Darcy’s equation; the saturation time of HS was 24 hr and that of W-RS was 48 hr. The soil water repellency was quantified with the water drop penetration time (WDPT) (Dekker et al., 2009). The soil samples were air-dried for one week indoors, then droplets of deionized water were placed on flattened subsamples with a pipette (0.48 ml/drop), and the complete infiltration time was measured. The mean time over seven droplet infiltrations was taken as the WDPT value. The measured physicochemical properties (P-CP) of the samples are listed in Table 1.
Table 1 Particle size distribution (%) and physicochemical properties of test soils