Soil microbial biomass carbon and phosphorus as affected by frequent drying–rewetting

Abstract

Drying and rewetting (DRW) events are very common in arable land. However, it is not clear how the frequency of DRW stress history influences soil carbon (C) and phosphorus (P) dynamics under field conditions. In this study, an arable loam calcareous soil was treated with simulated farming practices that included wheat straw and nitrogen incorporation and three DRW cycles at intervals of 14 days during a 90-day experimental period of incubation at 25°C. The DRW events significantly increased cumulative CO2-C evolution, but the increase rate of cumulative CO2-C evolution declined with increasing DRW cycles. Microbial biomass C (MBC) and P (MBP) decreased by 9–55% and 9–29%, respectively, following each DRW event, but recovered to the level before DRW treatment within 7 days. Frequent drying and rewetting caused significant increases in both extractable organic C and NaHCO3-extractable P, by 10–112% and 10–18%, respectively. The fluctuation of the tested parameters became less with increasing frequency of DRW cycles. Changes in microbial biomass, either MBC or MBP, were poorly correlated with those of extractable organic C and NaHCO3-extractable P. Overall, frequent DRW cycles had much stronger and longer lasting impact on soil biomass P dynamics than biomass C. These findings may imply certain links among soil moisture, microbial activity and nutrient bioavailability that are important in water and nutrient management.