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| Carbon management index as an indicator for changes in soil organic carbon pool under conversion from cropland to forestland |
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Abstract Soil organic carbon pool and its indicative indices including carbon management index (CMI), ratio of labile organic carbon (LOC) to total organic carbon (TOC), and non-labile organic carbon (A) were investigated for three typical kinds of forestlands: Caragana, Buckthorn, and Robinia, which have been converted from cropland for 10 to 40 years in Loess Hilly Area. Our objective was to determine the indicative capacity of CMI for changes in soil organic carbon. In general, the contents of TOC and LOC at 0~100 cm soil depth increased significantly. At 0~40 cm soil depth, soil organic carbon increased 10 years after conversion from cropland to forestland, while at 40~100 cm soil depth it began to show increases 20 years after conversion. Among the carbon indices, LOC/TOC (0.35~0.75) and A (0.25~0.42) did not increase with the increasing carbon pool during long-term conversion in the three kinds of forestlands indicating that they only reflected the active extent of soil carbon pool. In contrast, CMI showed increasing trends with soil carbon pool and its labile fraction, with greater increases for shallower soil (0~40 cm) and lower increases for deeper soil (40~100 cm), as confirmed by a positive linear correlation between CMI and content of carbon pool. Moreover, after 40 years of farmlands being converted to forestlands, CMI was significantly different among forestlands with an order: Robinia > Buckthorn > Caragana, which was the same sequences of TOC and LOC in the three forestland soils. Thus, CMI could be a better quantitative and qualitative indicator for the changes in soil organic carbon pool under conversion from cropland to forestland.
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Received: 19 June 2012
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