Impacts of landform, land use and soil type on soil chemical properties and enzymatic activities in a Loessial Gully watershed

Understanding the relationships among soil properties and, in turn, their relationships with landform, land use and soil type is essential for assessing soil quality and soil productivity. In this study, we examined the differences in the chemical properties and enzymatic activities of soils in a variety of landforms (plateau land, sloping land, terraced land and gully bottoms), land uses (woodland, grassland, cropland and orchard) and soil types (Chernozems, Cambisols and Regosols) in a gully watershed on the Loess Plateau, China. In total, 202 samples of surface soil (0-20 cm) were collected from different representative landscape units of the watershed. The chemical properties and enzymatic activities of the soils were measured. The results showed that chemical properties and enzymatic activities of the soils were all significantly influenced by landform, land use and soil type. There were interactive effects between landform and soil type. Soil pH varied the least, while invertase activity varied the most with landscape conditions. Soil pH, cation exchange capacity, organic carbon and total nitrogen contents, and enzymatic activities were all highest on plateau land and lowest on terraced land. Soil organic carbon and total nitrogen contents and alkaline phosphatase and invertase activities were higher in Chernozems than in Regosols, but the opposite trend was noted for pH, cation exchange capacity and catalase activity. Significantly higher values for most soil properties or enzymatic activities occurred in combinations including plateau land, Chernozems or Regosols. Soil pH was significantly lower in woodland soils than for other land uses, whereas the other properties had higher values in grassland and woodland soils than in orchard soils. The results from this study indicate the roles of landform, land use and soil type on the spatial patterns of chemical properties and enzymatic activities of soils and suggest that crops and orchards should be arranged on plateau land, and grasses and woodland on terraced and sloping land, respectively, for better economic and ecological efficiency in the area.