Field Study on Preferential Flow under Different Land Uses in the Loess Hilly Region

Evaluating the effects of different land uses on soil preferential flow is essential to improve the decision support systems for water management in the Loess hilly region in China. The objective of this study was to assess the response of preferential flow to different land uses (cropland, woodland, grassland). The study site was located in the Changwu Agri-ecological Experiment Station of the Chinese Academy of Sciences. In these experiments, an amount of 100 mm of Brilliant Blue dye solution was irrigated into the soil at constant heads of 10 mm, several vertical profiles were prepared to visualize dye stain patterns after each experiment, and photographs of the dye profile were processed by image analysis to discriminate stained and unstained areas. The results demonstrated that the preferential flow obviously existed in three land uses. The highest dye coverage was found at the soil depth of 0∼10 cm, while the dye area presented serrate dye peak, dye island or dye loop below 10 cm. The average depth of dye infiltration area (D_ave) was found highest in woodland (35.31 cm) followed by cropland (25.75 cm) and grassland (24.49 cm). The average value of maximum depth of dye infiltration (D_max) was significantly higher in grassland (49.93 cm) and lower in woodland (64.50 cm) and cropland (58.22 cm). The results indicated that vegetation types and initial moisture content would be the key factors affecting the preferential flow. This paper would be helpful in soil moisture and nutrient management in the hilly region of Loess Plateau.