Microbial Respiration and Nitrogen and Phosphorus Mineralization in Cow Dung-Amended Soils Depending on Moisture Contents: a Microcosm Study

Moisture is one of the most critical factors affecting nutrient mineralization in soils due to its effect on microbial activities. This study was carried out to determine the optimum moisture content that enhances microbial mineralization of N and P from organically amended ultisol and oxisol. One kilogram (1 kg) portion of air-dried samples of loamy sand and sandy clay loam was amended with composted cow dung at the rate of 10 g kg(-1). The soils' moisture contents were adjusted to 10, 30, 50, 70 and 100% of their field moisture capacities (FMC), and incubated for a period of 10 weeks in the laboratory. Microbial respiration measured as CO2 evolution and the concentrations of mineralized N and P in the amended soils were determined fortnightly for the 10-week period. There was significant positive correlation between moisture content and CO2-C, and between CO2-C and mineralized N. Concentrations of CO2-C, mineralized N and P were highest between 50 and 70% of the soils' FMC and lowest at 10 and 100% of the FMC. Varying moisture contents had clear significant effects on microbial mineralization of N and P in soils. Microbial mineralization of N and P from the cow dung-amended soils was optimized at the moisture levels ranging from 50 to 70% of the test soils' FMC.