Impact of Soil Management on Organic Carbon Content and Aggregate Stability

Abstract

Soil cultivation influences organic carbon storage and soil structures. To evaluate the impact of different soil‐management practices on soil organic carbon (SOC) pools and aggregate stability in black soils, SOC in whole soil, various size aggregates, and density‐separated fractions from three long‐term experiments (20 years) was examined. The three soil‐management systems were grassland (GL), bare land (BL), and croplands. The croplands had two treatments: nitrogen and phosphorus fertilizer application (NP) and NP together with organic manure (NPM). The SOC in the 0‐ to 10‐cm layer decreased in the order NPM>GL>NP>BL and also declined with the soil depth. The SOC of GL increased by 9.7% as compared to NP after 20 years of natural vegetation restoration. The SOC of NPM increased by 11% over NP after 13 years of organic manure application. The percentages of water‐stable aggregate (>0.25 mm) (WSA>0.25mm) decreased in the order GL>BL>NPM>NP in the top 0‐ to 20‐cm horizon. WSA>2mm, the most important fraction for carbon (C) storage in GL and NPM, accounted for 33 and 45% of the whole soil for GL in the depths of 0–10 and 10–20 cm, respectively, and 25 and 18% for NPM in the same soil layers. A significant positive correlation was found between the C stored in WSA>2mm and total SOC (r=0.81, P<0.05) and between the mean weight diameters (MWD) of aggregates and total SOC (r=0.78, P<0.05). Water‐stable aggregate0.25–2mm was the largest fraction of WSA>0.25mm, ranging from 54 to 72% for the 0‐ to 10‐cm layer and 46 to 71% for the 10‐ to 20‐cm layer; thus these aggregates would play a major role in soil sustainability as well as the resistance to soil erosion. The organic carbon (OC) of heavy fraction (HF) accounted for 94–99% of the OC in the WSA0.25–2mm, whereas free particulate organic matter (fPOM) and occluded particulate organic matter (oPOM) contributed a minor fraction of the OC in the WSA0.25–2mm, suggesting that C sequestration in HF could enhance the stability of aggregates and C pools in black soil.