A quantitative study of the influence of soil organic carbon and pore characteristics on the stability of aggregates of the karst peak-cluster depression area in Southwest China.

Purpose: Rock desertification is the most serious ecological problem in karst areas and can easily cause soil structure instability. The aim of this work was to analyze the influences of organic carbon, carbon components and pore structural differences on the stability of aggregates in rocky desertification areas. Materials and methods: Soil samples were collected from the karst peak-cluster depression area in Southwest China. Soil aggregate stability was determined by the Le Bissonnais (LB) method. The relationship between variables was analyzed via the structural equation model (SEM). Results and discussion: There were significant differences in the stability of aggregates among different land uses in the study area: secondary forest (SF) > coppice forest (CF) > plantation forest (PF) > citrus plantation (CP) > cultivated land (CL). The main crushing mechanisms of aggregates were slaking and mechanical failure. Aggregate pores were mainly < 30 μm storage pores, with pore throat diameters concentrated in the 0–20 μm range, which was associated with the cohesive soil texture of the study area. The pore connectivity of aggregates was better in SF and CF, followed by PF, while CP and CL had lower colloidal material contents, isolated pore structure and poor connectivity due to the heavy application of inorganic fertilizers and influences from human disturbances. Conclusions: SEM analysis showed that SOC and POC determined aggregate stability, mainly by directly or indirectly influencing aggregate porosity and the number of storage pores. The POC was the main variable in organic carbon composition to determine the pore characteristics and stability of aggregates. To meet the bidirectional demand of production and improvement of soil structure, it is necessary to rationally distribute fertilizer and reduce disturbance frequency in agricultural production land. [ABSTRACT FROM AUTHOR]