ATP, respiration, phosphatase, and pectinolyase were measured in samples taken from Montana coal strip mine spoils reclamation plots during 1975 and 1977. ATP correlated with respiration and pectinolyase, for the 1975 samples, and with respiration and phosphatase for the 1977 samples. Respiration correlated with phosphatase in the 1977 samples. ATP also showed a significant correlation with the sum of the other measurements for both years. Respiration correlated significantly with the sum of all other measurements only in the 1977 samples.
ATP was concluded to be the most satisfactory measurement of soil microbial activity in these samples. Arguments are presented for the use of ATP as an index of microbial activity in these developing soils.