Soil Aggregates Stability and Carbon Density Under Three Plantations on Loess Plateau, China

Abstract [Background] This paper aimed to research the influence of types of plantations on soil aggregate stability and carbon density. The soils of Robinia pseudoacacia, Pinus tabulaeformis and M. pumila plantations were selected as the research objects in the south of Loess Plateau. The mass percentages of soil water stable aggregates with different sizes were measured by fast wetting method, and then, the mean weight diameter (MWD) was calculated to asses soil aggregate stability. Soil organic carbon, inorganic carbon and bulk density were analyzed using traditional analysis methods. The roles played by soil organic and inorganic carbon in the formation of water stable aggregates were discussed. [Results] The content of soil organic carbon and MWD was significantly higher in P. tabuliformis plantation compared with R. pseudoacacia and M. pumila plantations. Conversely, the content of soil calcium carbonate and total carbon density was the lowest in P. tabuliformis plantation. Soil organic carbon was the highest at the surface soils (0-10 cm), which was 2.21-3.96, 2.10-3.00 and 1.65-2.53 times compared with subsurface soils in Robinia pseudoacacia, Pinus tabulaeformis and M. pumila plantations respectively. While soil carbonate calcium and inorganic carbon density fluctuated with the increasing of soil layers. Aggregate organic carbon increased while carbonate calcium content decreased with the increasing of aggregate size respectively. [Conclusion] We concluded that: (1) P. tabuliformis played a more important role in soil organic carbon sequestration compared with R. pseudoacacia and M. pumila; (2) there was a threshold value of carbonate calcium content, when it was lower or higher than this threshold, it had positive or negative correlation with MWD; (3) bigger water stable aggregates had higher soil organic matter and lower carbonate calcium.