Potential C and N mineralization and microbial biomass from intact and increasingly disturbed soils of varying texture

Potential C and N mineralization and soil microbial biomass C were determined following disturbance (i.e. drying and sieving) pretreatments in ®ve soils varying in texture (30±350 mg clay gÿ1 soil) from the southern Piedmont USA. Soil disturbance by drying (i.e. rewetting following drying at 558C for 72 h) of intact soil cores resulted in a ̄ush of C mineralization (70% to 2.5-fold greater) during 0±3 d of incubation, but was not signi®cantly di€erent during 3±10 and 10±24 d periods compared with ®eld-moist-intact soil cores. Soil disturbance by sieving resulted in greater C mineralization earlier than later in the incubation and led to signi®cant immobilization of N of surface soil where respiration was highest. Increasing soil disturbance through smaller sieve openings resulted in a 10±60% greater ̄ush of C mineralization that may have been due to disruption of macroaggregates, which protected soil organic C. With a conditioning period of 10 d following rewetting of dried soil, soil microbial biomass C was una€ected by drying or extent of sieving. Soil texture (i.e. clay content) did not interact with disturbance e€ects. Immobilization of N was predominant in surface soils (0±40 mm) of this bermudagrass pasture, where mineralizable C was very high. Carbon mineralization during 0±3 d was highly related (r =0.9620.04) to C mineralization during 0±24 d, basal soil respiration and soil microbial biomass C, although increasing soil disturbance (i.e. drying and extent of sieving) altered these relationships in a predictable manner. I conclude that dried and coarsely sieved soil compares favorably to ®eld-moist-intact soil cores for estimating soil microbial biomass and potential activity in landscapes scoured by various degrees of erosion. Published by Elsevier Science Ltd.