Microbial biomass dynamics and soil wettability as affected by the intensity and frequency of wetting and drying during straw decomposition

Water repellency is influenced by soil management and biological process. We carried out a 60-day laboratory incubation experiment to evaluate the effects of straw amendment, together with the intensity and frequency of wetting and drying (W/D), on microbial processes and water repellency. One W/D cycle consisted of 1.5-day wetting at -0.03 kPa from the soil core bottom and different drying lengths in a temperature-controlled laboratory, resulting in different drying intensities. At a regular interval, soil respiration rate (SRR) on drying and wetting, soil microbial biomass C and N (SMB-C and N), and soil water repellency (SWR) after the wetting were measured simultaneously. Rice straw amendment had a greater effect on SRR, but smaller influences on SMB and SMB-C : N than W/D frequency and drying intensity. The first W/D caused the largest decrease in soil respiration and the soil respiration recovered partly in the subsequent W/D cycles. The increase in SMB and SMB-C : N as well as metabolic quotient with W/D frequency and intensity suggested a shift of microbial community from bacterial dominance to fungal dominance. SWR was significantly related to SMB-C (R-2 = 0.689, P < 0.001). However, this study was limited to these indirect measurements. Direct measurements of fungal biomass and microbial community are needed in the future. The results suggest that rice straw amendment in dry season may increase C sequestration due to reduced decomposition and stabilize soil structure due to the enhancement of microbial induced water repellency.