Microbial C and N dynamics during mesophilic and thermophilic incubations of ryegrass

摘要

Laboratory studies were conducted to determine C and N dynamics during the decomposition of ryegrass straw under mesophilic and thermophilic conditions. A KCof 0.61 was developed for the chloroform-fumigation extraction method to estimate microbial biomass C. These estimates showed that the C and N requirement of the thermophilic biomass was approximately 50 of the mesophilic biomass. There was no relationship between chloroform-fumigation microbial biomass estimates and plating of microorganisms from straw on specific media. Mineralized C was measured as 185 and 210 g kg-1straw in the 25°C and 50°C treatments, respectively. The efficiency of microbial substrate use, on a total straw basis, was 34 and 28 in the 25°C and 50°C incubations, respectively. The level of soluble C declined more slowly than total C mineralization at both temperatures, indicating that a portion of the labile C was not readily biodegradable. The addition of N decreased the rate of C mineralization at both temperatures. The reduced N requirement of the thermophiles explains why rapid degradation of the high C:N residue occurred without additional N or the need for the addition of a low C:N ratio substrate. Additional inoculum did not affect the decomposition process. We conclude that the promotion of thermophilic biomass activities, through composting for example, may prove useful in upgrading agricultural wastes for introduction into sustainable cropping syst