Microbial biomass and metabolic quotient of soils under different land use in the Three Gorges Reservoir area

Alternative land use systems, and especially agroforestry, are currently being promoted in the Three Gorges area to enhance soil retention and improve soil quality. The soil microbial biomass (C-mic) is intimately associated with the build up of organic matter (C,,). Different land uses including mixed cropping systems were compared with respect to their soil microbial biomass, basal respiration (R), the C-mic/C-org ratio and metabolic quotient. Microbial biomass C of citrus/wheat soils ranged widely from 54 to 194 mug g(-1) soil and formed 0.48-2.11% of the total organic C. For forests, citrus/wheat (wheat area) and tea bush, microbial biomass C as a percent of soil organic C were roughly four times that for citrus and citrus/wheat (citrus area). There were no significant differences between tea bush and forest in microbial biomass C, respiration rate and metabolic quotient. Significant relationships between microbial biomass C, C-mic/C-org ratio and readily available N were found for all samples except citrus/wheat (wheat area) and forest soils. Terraced systems and especially terraced agroforestry promoted the retention of organic matter and this was reflected in the microbial indicators. (C) 2003 Elsevier Science B.V. All rights reserved.