Wind erodibility of major soils in the farming-pastoral ecotone of China

Wind erosion and desertification are severe problems in Chinaʹs farming-pastoral ecotone. In this study, wind erodibility of five major soils in both uncultivated and simulated cultivated conditions, were determined through wind tunnel tests at nine wind speeds ranging from 10 to 26 m s−1. The average wind erosion rate (g m−2 min−1) under the uncultivated condition (q0) for the five soils could be set in the order: chestnut soil (28.5)>brown soil (24.8)>sierozem (21.8)>chernozem (19.9)>fixed sandy soil (11.4). The highest natural wind erosion might take place in the semi-arid steppe zone where the Chestnut soils predominate. Cultivation can significantly accelerate wind erosion, the mean wind erosion rate under the cultivated condition (qc) for all five soils was 743.7 g m−2 min−1 in the following order: sandy soil (3313.2)>brown soil (227.2)>chernozem (221.8)>sierozem (85.1)>chestnut soil (81.2). For both the uncultivated and cultivated soil samples, the relationship between wind erosion rate (q) and wind speed (U) could be expressed in general as q=A eBU (A and B are constant coefficients). There was a critical wind speed for each soil type except for the sandy soil. Below the critical wind speed, cultivation reduced wind erosion rate possibly due to soil clodiness and roughness effects. Above the critical speed, cultivation greatly intensified wind erosion rates due to the break down of the original soil structure. The critical wind speed measured at 20 cm above the soil surface was 20 m s−1 for the brown soil, 14 m s−1 for chernozem and the chestnut soils, and 10 m s−1 for the sierozem. Among the five tested soils, the high wind erosion rate of the cultivated sandy soil showed its extreme sensitivity to cultivation, possibly because of the structureless nature of the loose sand. The “effect of cultivation on wind erosion” index, η (=qc/q0), increased exponentially with the increase of wind speed, indicating that under higher wind speed conditions, cultivation could result in more severe wind erosion.