| Abstract: | Abstract On air‐drying, the ATP contents of two moist soils fell to about one quarter of their original values. When a freshly‐sampled soil (field temperature 5.5°C) was stored moist (43% water holding capacity) for 7 days at 25°C the ATP content increased from 4.54 to 7.84 μg ATP g‐1 soil. Storage at 10°C caused a smaller increase; to 5.39 μg g‐1 soil. Microbial biomass C also increased on storage but the relative increase was less than that of ATP. Thus the biomass C/ATP ratio fell from 234 in the freshly sampled soil to 168 in the soil stored moist for 7 days at 25°C. The ATP content declined to less than half its starting value if storage was under waterlogged conditions. The ATP method for determining microbial biomass in soil depends on the use of a constant factor (5.85 mg ATP g‐1 biomass C) for converting ATP content to biomass C. This factor came from work on soils that had been stored moist at 25°C for several days before biomass C and ATP measurements were made: it is only applicable to soils that have been stored in this way. |
