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