Soil microbial biomass and enzyme activity in subarctic agricultural and forest soils

Summary Microbial biomass, activities of dehydrogenase, phosphatase, and urease, and numbers of ammonium oxidizers were determined at monthly intervals on soil samples obtained from an on-going tillage residue-management study during the summers of 1985 and 1986. The site was cleared of black spruce (Picea mariana, Mill.) in 1979 and has been planted to spring barley (Hordeum vulgare) since 1982. Tillage treatments were no-tillage or disked twice, and residuemanagement treatments were removal of stubble and loose straw or leaving all straw on the plots. Microbial biomass and enzyme activities were moderate to high in the Ap horizon but very low in the B horizon. There was no difference in any parameter measured due to tillage or residue management. In 1986, comparisons were made between the Ap horizon and the agricultural soil and the A horizon of the soil beneath an adjacent black-spruce forest. Total microbial biomass and enzyme activities were generally greater in the forest soil than in the agricultural soil. However, specific activity of the biomass was generally greater in the agricultural soil. Soil microbial biomass and urease activities of both agricultural and forest soils were similar to those reported for warmer climates, but dehydrogenase activity was higher and phosphatase was lower.