Effects of Different Land-Use Systems on Soil Aggregates: A Case Study of the Loess Plateau (Northern China)

Soil aggregate stability is an important indicator for controlling soil losses and can improve soil quality, particularly in an area such as the Loess Plateau. The objective of this study was to estimate the differences in soil aggregates across six different land-use systems (grassland, apple orchard, abandoned apple orchard, cropland maize, cropland wheat, and shrub-grassland). For this purpose, dry and wet sieving techniques were employed to assess aggregate content and aggregate stability. Higher percentages of water stable aggregates were observed in the abandoned apple orchard and shrub-grassland at 63% and 61%, respectively. The maximum dry aggregate stability (%) was recorded at 78% and 77% in both wheat cropland and common apple orchard, and the abandoned apple orchard was only 74%. Both mean weight diameters and geometric mean diameters of aggregate were recorded as higher in grassland, shrub-grassland, and the abandoned apple orchard, than the other land uses. The formation of soil aggregates and their stability were positively correlated with soil organic carbon content and root biomass of different plant communities. Higher amounts of soil organic carbon content were noted in the abandoned apple orchard, common apple orchard, and natural grassland at the 0–20 cm soil layer. The results of the correlation coefficient showed a positive significant correlation between the mean weight diameter, geometric diameter, root biomass, and soil organic carbon content. Conclusively, the type of land use affected the soil aggregation and distribution of size fractions; the small fractions of the aggregates formed large fractions by combining with fresh organic matter, and increased soil organic carbon concentrations were closely linked with the formation of macro-aggregates. Thus, converting slope farmland to forestland and grassland could improve water-stable aggregate and reduce soil disturbances in areas (like the Loess Plateau) with the highest erosion risk.