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Based on the long-term observation and from the viewpoints of water balance and runoff-and sediment generation, this paper studied the generation processes of runoff and sediment on two typical woodlands, artificial P. tabulaeformis and secondary natural P. dadidiana, and uncultivated slope-land in Loess Plateau under hypo-rainfall. The results showed that within the range of 5.0 - 50.0 mm rainfall, the total interception of canopy and litter was 15.45 % - 56.80 % for P. tabulaeformis and 20.56% - 47.81% for P. dadidiana, and decreased with increasing rainfall. Woodlands had a higher soil water infiltration capacity than uncultivated slope-land, especially in 0-20 cm soil layer. Both the two woodlands did not generate runoff under regular rainfall. Under the assumed rainfall of 2.5 mm x min(-1) intensity and 30 min duration, P. dadidiana stand did not produce runoff, but the runoff velocity and sediment-carrying capacity of uncultivated slope-land were 23.5 times, and runoff shearing stress and energy were 8 times as much as P. tabulaeformis stand. The runoff-and sediment generation on P. tabulaeformis stand decreased by 87.6% and 99.4%, respectively, compared with those on uncultivated slopeland, which was well accorded with the average observed value in runoff plots during 1988 - 2000. The theoretical analysis on the generation mechanism of woodland runoff and sediment may be effective to evaluate the benefits of forest in soil and water conservation.

For the sustainable development and ecological construction in the loessial semiarid region, it is important to describe the variability of slopeland soil properties and the affecting factors of slopeland productivity. In this study, soil samples were taken from eroded steep slopeland, and leaf area index (LAI) and above-ground biomass (AGB) were measured at the sampling locations. The soil water content (WC) of 2 m depth at 20 cm intervals, and the soil organic matter (OM), total nitrogen (TN), total phosphorus (TP), available nitrogen (AN) and available phosphorus (AP) contents of 0-20 and 20-40 cm soil layers were determined in the laboratory. The results showed that the majority of the properties was normally distributed, and the nutrient contents were higher in 0-20 cm than in 20-40 cm layer, but the variations of soil nutrients were much smaller in 0-20 cm than in 20-40 cm layer. Soil nutrients had a significantly larger variation than soil moisture. Soil nutrient contents in 20-40 cm layer kept increasing from upslope to downslope, while those in 0-20 cm layer varied slightly. Slope topography had more obvious impact on soil organic matter, total nitrogen and available phosphorus than other affecting factors. Soil water and nutrient contents on the shallow gully trough were notably higher than those on the upslope, but above-ground biomass was less than that on the upslope. Though longitudinal slope (35 degrees-45 degrees) was obviously larger than the horizontal one (5 degrees-10 degrees), horizontal slope position had a greater influence on soil nutrients, but much weaker effect on soil moisture than longitudinal direction. There were significant correlations between 0-120 cm soil moisture and 20-40 cm soil nutrients, and among soil nutrients except 0-20 cm soil available phosphorus. Slopeland position had a great impact on soil moisture and nutrients, but soil moisture and/or nutrients had no significant impact on above-ground biomass.