Spatial variation of topsoil features in soil wind erosion areas of northern China

The particle size distribution (PSD), contents of soil organic matter (SOM) and calcium carbonate (CaCO3), and surface gravel coverage (GC) are the crucial factors affecting topsoil features, and consequently, these factors influence soil wind erosion and land use. The aim of this study is to understand the topsoil features in northern China, which is one of the regions of the world that experiences the most severe soil wind erosion. We used the topsoil data of the PSD, SOM content, CaCO3 content and GC derived from 610, 608, 503 and 2372 topsoil sampling sites, respectively. The results of the calculations and statistics showed that the particles in the topsoil were generally coarse; the areas of sandy loam, loam, loamy sand and silty loam accounted for 39.53%, 21.05%, 16.31% and 12.15% of the total area, respectively, and the other eight types of soils combined accounted for 10.96% of the total area. The areas with SOM contents of ≥5%, 1-5% and <1% accounted for 5.58%, 52.62% and 41.79% of the total area, respectively. The areas with CaCO3 contents of ≥10%, 5-10%, 1-5% and <1% accounted for 19.46%, 32.98%, 39.30% and 8.26% of the total area, respectively, in which sandy loam and silty loam soils with a CaCO3 content of 1-5% were the most susceptible to wind erosion. The areas with GC of 50-100%, 20-50%, 5-20% and <5% accounted for 10.77%, 12.80%, 18.90% and 57.53% of the total area, respectively; the areas with GC of >20% were mainly distributed in the northwest regions, which were occupied by Gobis and gravel deserts with rare vegetation. The areas with higher intensity levels of soil wind erosion were mainly distributed in the areas with higher values of gravel coverage; this seemingly abnormal phenomenon is caused by an abundance of erodible particles (0.02-0.84 mm in diameter) hiding amongst the gravels, rare vegetation and long duration of effective wind speeds that cause erosion.