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 five soils varying in texture (30–350 mg clay g−1 soil) from the southern Piedmont USA. Soil disturbance by drying (i.e. rewetting following drying at 55°C for 72 h) of intact soil cores resulted in a flush of C mineralization (70% to 2.5-fold greater) during 0–3 d of incubation, but was not significantly different during 3–10 and 10–24 d periods compared with field-moist-intact soil cores. Soil disturbance by sieving resulted in greater C mineralization earlier than later in the incubation and led to significant immobilization of N of surface soil where respiration was highest. Increasing soil disturbance through smaller sieve openings resulted in a 10–60% greater flush 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 unaffected by drying or extent of sieving. Soil texture (i.e. clay content) did not interact with disturbance effects. 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 (r2=0.96±0.04) 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 field-moist-intact soil cores for estimating soil microbial biomass and potential activity in landscapes scoured by various degrees of erosion.