Rewetting Intensity Influences Soil Respiration and Nitrogen Availability

It is not clear how different rewetting intensities (rapid, slow or partial rewetting) influence soil respiration and nitrogen (N) availability. Moist soil left unamended or amended with low C/N faba bean residue and incubated for 21 days was dried to <5% WHC within 3 days. After 14 days of incubation, dry soils were rewetted to 50% water holding capacity (WHC), once within few seconds (rapid), by two applications at 25% WHC each, with 6-h interval between rewetting events (slow), or single application at 25% WHC (partial). The soils were further incubated for another 14 days. One day after rewetting in unamended and amended soils, respiration rate followed the order slow > rapid > partial rewetting. From day 4 onwards, moisture treatments differed little in respiration rate. In unamended soils, the rewetting intensity had little effect on available N. But 1 day after rewetting, MBN was lowest in CM, and twofold, fourfold and tenfold higher with rapid, slow and partial rewetting, respectively. In amended soils 1 day after rewetting, available N was about twofold higher in CM and with rapid than slow and partial rewetting, while MBN was about twofold higher with CM and rapid rewetting than slow and partial rewetting. Treatments differed little in available N and MBN 7 and 14 days after rewetting. Slow rewetting induced greater soil respiration and microbial N uptake than rapid rewetting. But effects were short-lived.