Differences in soil nutrient and carbon pool management index under different land management and utilization modes in karst slope region

The study area, located at Huanjiang karst eco-system station of Chinese Academy of Sciences, falls into typical karst peak cluster depression landscape unit. In order to provide scientific basis for determining reasonable method of land management and utilization and further improving land quality under different slope land use conditions in karst region, the differences in soil nutrient and carbon pool management indexes in different land management and utilization conditions were investigated in this study. Six types of land use were implemented on the karst slope, via the measures of natural afforestation, maize planting, pasture planting, vegetation burning, tree/grass mowing and mowing plus root removal. Afterwards, the soil samples in 0 to 20 cm depth were collected at 5 localities respectively in the upper, middle and lower slope of each land treatment, from which the soil nutrient content, organic carbon, active organic carbon and carbon pool management indexes were measure, respectively. The results showed that the contents of soil nutrient and organic carbon and carbon pool management indexes were significantly different at different treated lands. The contents of total nitrogen, total phosphorus, available nitrogen, available potassium, organic carbon and active organic carbon in soils decreased with the increase of human interference on soils, and the above mentioned indexes under maize planting, pasture planting and mowing plus root removal treatments were significantly lower than those of natural afforestation and burning treatments, because of much more human interference on the soils. The lowest contents of total nitrogen, total phosphorus, and available nitrogen occurred on maize planting lands, while the lowest content of available potassium on both maize planting and mowing plus root removal ones. The contents of total potassium and available phosphorus in the soils reached the highest on the land after maize planting treatment, but their lowest values occurred along with the tree/grass mowing treatment. The highest content of slowly available potassium in the soils occurred on the land with afforestation treatment, followed by that of maize and pasture planting treatments, while the lowest was on tree/grass mowing treatment. The lowest contents of soil organic carbon and active organic carbon were on those associated with maize planting treatment, decreased by 37.04% and 41.14%, respectively, comparing with the contents related to afforestation treatment. Except for the afforestation, the lands with the other treatments had a significant decrease in the carbon pool management index, of which the lowest occurred on those with maize planting and burning treatments. In addition, the contents of total nitrogen, total phosphorus, total potassium, available nitrogen and organic carbon in soils decreased along with the slope altitude. From this study, it is understood that in ecological vulnerable karst region, natural afforestation is the most beneficial to the maintenance and improvement of soil nutrient and carbon pool management index. On contrary, by the increase of human interference on soils, the soil nutrient content and the carbon pool management index can be significantly reduced.