3.1 Study Area
This study was conducted in six experimental plots, three located in each of the Xindiangou (XDG) and Chabagou (CBG) watersheds, which are all in the hilly region of the Loess Plateau (Fig. 1).
The XDG watershed (latitude: 37°29′N, longitude: 110°08′E; elevation: 990–1,010 MASL; area: 30 km2) is located in Suide county. It has a mean annual temperature of 8 °C and a mean annual precipitation of 470 mm, most of which falls between June and September. The main soil type is silty loam. Soil particle size distribution and physical characteristics are highly homogeneous within the 0–30 cm surface soil layer (Liu et al., 1994).
The CBG watershed (latitude: 37°31′N, longitude: 109°47′E; elevation: 900–1,100 MASL; area: 205 km2) is located in Zizhou county. It has a mean temperature of 8 °C and an mean annual precipitation of 450 mm, of which more than 70% occurs from July to August, usually falling as high-intensity and short-duration rainstorms. The CBG watershed possesses Malan loess with less than 40% clay particles, leading to its large porosity and easy erodibility (Kimura et al., 2005).
The three experimental plots in the XDG watershed were planted with alfalfa (Medicago sativa L.), sweet clover (Melilotus suavcolen ) and millet (Setaria italica ) during the monitoring period. In the CBG watershed, pasture (Arundinella hirta ), potato (Solanum tuberosum  L. ) and millet were grown in the three respective experimental plots during the study period (Table 1).