Protective function of narrow grass hedges on soil and water loss on sloping croplands in Northern China

Soil and water loss have become a critical problem on sloping croplands in Northern China. Vetiver grass (Vetiveria zizanioides (L.) Nash) hedges have been suggested to be effective in preventing soil and water in tropical and subtropical regions but appear to be ineffective in temperate regions because they cannot withstand the low temperatures in winter time. Here we evaluated the soil and water conservation function of two native grass hedges, Pennisetum alopecuroide (Pennisetum alopecuroides (Linn.) Spreng.) and Arundinella hirta (Arundinella hirta (Thunb.) C. Tanaka), in Northern China. Three hydrologically isolated plots were used to test each combination of hedges and slope gradients (5%, 10%, 15% and 20%) under different levels of rainfall intensities (i.e. 14, 22, 36 and 63 mm h−1). The experiments were carried out on a different type of croplands (i.e. soybean (Glycine max (L.) Merr.), winter wheat (Triticum aestivum L.), alfalfa (Medicago sativa L.), and no crops) alternatively in a four-year period (2006–2009). Comparing to the case of using no grass hedges, on average Pennisetum hedges reduced soil loss by 84% and overland flow by 68%, and Arundinella hedges reduced soil loss and overland flow by 55% and 38%, respectively. These results suggested that both Pennisetum and Arundinella hedges provided effective protection against soil and water loss, and Pennisetum hedges had almost doubled efficacies over Arundinella hedges. Their protection efficacies varied across different types of croplands. However grass hedges action alone, under the experimental conditions, did not provide sufficient protection under steep slope and intense rain conditions. It was found that the impact of grass hedges on the control of runoff and erosion is more significant than rain intensity and slope gradient. The influence of root architecture on overland flow was assessed. One empiric model was derived to describe the influence of the independent variables (including slope gradient, rainfall intensity, age and type of grass hedges, and type of crops) on overland flow and soil transport and simulated the extent of protection under the range of experimental conditions. These findings may be helpful in the remediation of serious soil and water losses on sloping croplands in northern China and similar regions.