Soil Aggregate Stability And Soil Organic Carbon Characteristics In Different Plantations In Karst Area

Studies on soil aggregates stability and their organic carbon distribution characteristics are active, however, few of them were carried out in Karst areas. In order to clarify the changes and influence factors of soil aggregates stability and their organic carbon characteristics in a Karst area located in Guangxi Zhuang Autonomous Region, soils from four main plantations [i.e., PinusmassonianaLamb, Eucalyptus, Phyllostachys heterocycla (Carr.) Mitford cv. Pubescens, and Cunninghamia lanceolata (Lamb.)Hook] and a natural secondary forest were investigated and analyzed in this study. Soil nutrient, soil aggregates stability, particle size distributions, and organic carbon contents in water-stable aggregates of surface (0～20 cm) and subsurface (20～40 mm) soil samples were tested and compared. The results are sumarised as follows:Adverse effects on soil quality had been found for areas where the natural secondary forests were transformed into artificial forests. Soil nutrient, soil aggregates stability (both water stability and mechanical stability), and soil carbon density in artificial forests were generally lower than that of natural secondary forests. For instance, compared with the natural secondary forests, the soil carbon density of the four artificial forests declined 12.2%-41.8%. The soil aggregates water-stability of surface soils was higher than that of subsurface soil for all of the four artificial forests, while the soil aggregates water-stability of the Cunninghamia lanceolata (Lamb.)Hook. plantation was the highest, and that of the Eucalyptus plantation were the lowest.Soil physical and chemical properties had little influence on mechanical stability of soil aggregates, but they were close related with water-stability of soil aggregates. After dry sieving treatments, soil physical and chemical indicators (total N, P, K, soil bulk density, soil organic matter) had non-significant correlation with mean mass diameter, geometric mean diameter and fractal dimension of soils, except that the total N had a significant correlation with the fractal dimension of soils. After wet screening treatments, soil physical and chemical indexes (except for total P, total K) were closely related with mass average diameter and geometric mean diameter of soils. The mean mass diameter had extremely significantly positive correlations with soil organic matter and total N, and had a significantly native correlation with soil bulk density. The geometric mean diameter were significantly positively correlated to soil organic matter and total N, and negatively correlated to soil bulk density. The fractal dimension and total N showed a significant positive correlation.The anti-erosion ability of soils could be enhanced by increasing contents of large aggregates (> 5 mm) and soil organic carbon. While, the increase of relivelively small aggregates with diameters less than 5 mm would reduce soil stability and anti-erosion ability. Contents of soil organic carbon could also been increased by increasing contents of large aggregates (>5 mm), since the maximum organic carbon contribution rates for four forests (except Eucalyptus plantations) appeared in large aggregates (>5 mm).The soil organic carbon density of the five forest types (Eucalyptus,PinusmassonianaLamb, Phyllostachys heterocycla (Carr.) Mitford cv. Pubescens, Cunninghamia lanceolata (Lamb.)Hook. plantation, and secondary natural forest) in the 0～40cm layer was 7.75,9.72,11.12,11.70, 13.32kg/m2, respectively. The soil organic carbon density of the five types of forests in the 0-20cm soil layer was higher than that in the 20～40cm soil layer. It was suggested that construction of Cunninghamia lanceolata (Lamb.)Hook. artificial forest in Karst area could increase soil carbon storage.