Rewetting of dry soil induces a flush of respiration, but less is known about the effect of the number of drying and rewetting (DRW) cycles on the distribution of respiration and how the length of the moist period influences respiration and microbial biomass in residue-amended soil. Two experiments were conducted. In the first experiment, the effect of number of DRW cycles on soil respiration and microbial biomass was assessed. We exposed a sandy loam amended with finely ground pea residues (C/N 26) to up to three DRW cycles, each cycle consisting of one week drying and one week moist incubation. Soils which were maintained moist throughout served as controls. The flush in respiration was greatest in the first DRW where it was 3 times higher than in the following cycles, but did not differ between the second and third DRW. Cumulative respiration at the end of the experiment was highest in the constantly moist soil and lowest with three DRW cycles (20% lower than in the constantly moist soil). Microbial biomass C did not differ between the constantly moist treatment and the DRW treatments on days 14 and 28, but at the end of the experiment (d 42) the MBC concentration was 40% higher in the treatments with 2 and 3 DRW cycles than in the constantly moist treatment. The second experiment was conducted to test the hypothesis that the amount of C respired at the end of the preceding cycle may influence respiration in the second cycle. In this experiment, the soil was maintained moist or subjected to two DRW cycles where the length of the moist period in the first cycle lasted between one and five days followed by 7 days dry. The second moist period was three days in all DRW treatments. Cumulative respiration at the end of the experiment was lowest in the soil with one moist day in the first cycle (1 mg CO2-C g(-1)) and highest in the constantly moist control (1.6 mg CO2-C g(-1)). Among the DRW treatments, cumulative respiration over the entire incubation period (two DRW cycles) was about 30% higher in treatments with four to five moist days in the first DRW than in the treatments with one, two or three moist days which did not differ in cumulative respiration. Cumulative respiration in the second cycle was about 30% higher in treatments with 1-2 moist days in the first cycle compared to treatments with 3-5 moist days. Both cumulative respiration in the second DRW cycle and in the second moist period were negatively correlated with cumulative respiration at the end of the first period. Microbial biomass C (MBC) differed little between the moisture treatments except for a 50% higher MBC concentration at the end of the first moist period in the treatment with 1 moist day. It can be concluded that cumulative respiration is reduced by DRW and that the negative effect of DRW on cumulative respiration is exacerbated if the moist period after rewetting is short. The finding that cumulative respiration in the second DRW cycle is negatively correlated with cumulative respiration in the first cycle indicates that substrate availability at the start of the second cycle plays an important role in respiration in the second cycle.

　　Rewetting of dry soil induces a flush of respiration, but less is known about the effect of the number of drying and rewetting (DRW) cycles on the distribution of respiration and how the length of the moist period influences respiration and microbial biomass in residue-amended soil. Two experiments were conducted. In the first experiment, the effect of number of DRW cycles on soil respiration and microbial biomass was assessed. We exposed a sandy loam amended with finely ground pea residues (C/N 26) to up to three DRW cycles, each cycle consisting of one week drying and one week moist incubation. Soils which were maintained moist throughout served as controls. The flush in respiration was greatest in the first DRW where it was 3 times higher than in the following cycles, but did not differ between the second and third DRW. Cumulative respiration at the end of the experiment was highest in the constantly moist soil and lowest with three DRW cycles (20% lower than in the constantly moist soil). Microbial biomass C did not differ between the constantly moist treatment and the DRW treatments on days 14 and 28, but at the end of the experiment (d 42) the MBC concentration was 40% higher in the treatments with 2 and 3 DRW cycles than in the constantly moist treatment. The second experiment was conducted to test the hypothesis that the amount of C respired at the end of the preceding cycle may influence respiration in the second cycle. In this experiment, the soil was maintained moist or subjected to two DRW cycles where the length of the moist period in the first cycle lasted between one and five days followed by 7 days dry. The second moist period was three days in all DRW treatments. Cumulative respiration at the end of the experiment was lowest in the soil with one moist day in the first cycle (1 mg CO2-C g(-1)) and highest in the constantly moist control (1.6 mg CO2-C g(-1)). Among the DRW treatments, cumulative respiration over the entire incubation period (two DRW cycles) was about 30% higher in treatments with four to five moist days in the first DRW than in the treatments with one, two or three moist days which did not differ in cumulative respiration. Cumulative respiration in the second cycle was about 30% higher in treatments with 1-2 moist days in the first cycle compared to treatments with 3-5 moist days. Both cumulative respiration in the second DRW cycle and in the second moist period were negatively correlated with cumulative respiration at the end of the first period. Microbial biomass C (MBC) differed little between the moisture treatments except for a 50% higher MBC concentration at the end of the first moist period in the treatment with 1 moist day. It can be concluded that cumulative respiration is reduced by DRW and that the negative effect of DRW on cumulative respiration is exacerbated if the moist period after rewetting is short. The finding that cumulative respiration in the second DRW cycle is negatively correlated with cumulative respiration in the first cycle indicates that substrate availability at the start of the second cycle plays an important role in respiration in the second cycle.