Soil organic carbon fractions and their stability under different land uses in wind erosion area of Northeast China.

Exploring the physical fractions of organic carbon and influencing mechanisms in grassland, forest, and farmland soils in wind erosion area can provide scientific basis for carbon sequestration, land utilization, wind prevention measure making, and fertility restoration of sloping farmland in the region. We examined the differentiation of aggregate organic carbon and density fractionation organic carbon in 0-15 cm soil layer across grassland, forest, and sloping farmland with 350 m long and 5° slope gradient in the wind erosion area of Meilisi District, Qiqihar, Heilongjiang, as well as the sloping farmland in the downhill section, middle section, and uphill section with every 100 m apart from the bottom to the top. The results showed that soil aggregates >2 mm were all destroyed across grassland, forest, and farmland soils, while the percentage of aggregates <0.053 mm was significantly higher than that of other sizes. The percentage of various soil aggregates, organic carbon content from density fractionations, and the proportion of organic carbon in the heavy fraction aggregates in farmland were significantly lower than that in grassland and forest soils. Soil aggregates in the uphill section of farmland were completely destroyed, and organic carbon content in various size aggregates and density fractionations gradually decreased with increasing slope. The proportion of organic carbon in the heavy fraction aggregates decreased, but that in light fraction aggregates increased gradually. Soil organic carbon and available potassium were key factors affecting aggregate stability, aggregate organic carbon content, and organic carbon content in density fractionations, while the loss of organic carbon in aggregate led to a decrease in aggregate stability. In summary, compared with grassland and forest soils, the stability of soil aggregates, the aggregate organic carbon content, the organic carbon content in density fractionations, and the proportion of organic carbon in heavy fraction aggregates in farmland all decreased in the wind erosion area of Northeast China. With the increases of slope, the aggregate organic carbon content, the organic carbon content in density fractionations, and the proportion of organic carbon in the heavy fraction aggregates in sloping farmland all decreased. Planting trees, conserving and expanding grassland area, and increasing the application of organic materials in sloping farmland in wind erosion area are effective approaches to stabilize and increase carbon storage, improve soil structure, and enhance soil quality.