Effects of contrasting agricultural management on microbial residues in a Mollisol in China

Microbial residue represents a significant amount of soil organic matter, and its component amino sugar can serve as time-integrated indicators that reflect chronic effects of agricultural management. We evaluated the influence of different land-use and fertilization treatments on the amounts and patterns of amino sugars (glucosamine and galactosamine) and muramic acid in a Mollisol (Udolls, USDA Soil Taxonomy System) in northeastern China. The treatments included: BL, bareland, without any vegetation; GL, restored grassland which allows plants to re-vegetate naturally; AL, arable land without any fertilizer; ALF, arable land with chemical fertilizer; and ALMF, arable land with chemical fertilizer and pig manure. The amino sugar concentrations differed significantly between various treatments after 26 years, with the order of ALMF > GL > ALF > AL > BL. This suggests that long-term contrasting management changed microbial residue accumulation in soil, which is strongly related to soil organic carbon content. The larger ratios of glucosamine to muramic acid in the GL plots than the AL and BL plots indicated a shift toward fungal-derived residues after 26 years of natural restoration. Our results suggested that different land-use and fertilization treatments clearly influenced amounts and patterns of microbial residues and their contribution to SOM accumulation, primarily due to differences in organic C inputs.