Long-Term Management Impacts on Soil C and Labile Organic C Part I: Vegetation Restoration and Fertilization.

ABSTRACT Labile soil organic carbon (SOCL) is an important indicator of soil quality and sensitive to soil management changes. This paper investigated the dynamics of total organic C (CTOT), and labile C (CLOC) in response to different soil managements in an experiment commenced in 1985 on a black soil in Hailun National Field Research Station. We also examined the effects of residues of grass and crops (Bare fallow, Grassland, Cropland) on CLOC measured by chemical fractionation using permanganate digestion, and further calculated carbon management index (CMI). In addition, we evaluated the effects of long-term fertilization (received no fertilizers, CK; N and P fertilizers, NP; N and P fertilizers along with pig manure, NPM) during1993¨C2005 on CLOC and CMI. The results indicated that different kinds of residues returned to soil had remarkable influences on the formation of CLOC. CTOT and CLOC under Bare fallow were observed to decline by 11.2 and 17.2% compared with those in 1985, by contrast, increases of 13.2and 39.9% were found in Grassland. SOC in cropland increased by 1.1% and CLOC declined by 12.6% , accordingly. CMI of Bare fallow and cropland decreased by 38.5 and 15.4, while an increase of 51.4 was observed in Grassland. Application of 30 t ha-1year-1 of organic manure increased CTOT and CLOC by 25.5 and 31.4%, respectively, as compared with no manure application to make them equivalent to, or greater than that of Grassland, and CMI increased by 33.1, correspondingly. There were similar significant positive correlations between C fractions and total N on both experimental sites but stronger relationships were found in the fertilizer-treated experiments. Key words: black soil£¨Udic Mollisols£©, organic carbon, labile soil organic carbon, carbon management index