Effects of three fertility amendments on soil dehydrogenase activity, organic C and pH

An Acadia silty clay and a Pugwash sandy loam were each fertilized with three rates of either composted chicken manure, fresh chicken manure, or synthetic fertilizer. The effects of these amendments on soil microbial activity (dehydrogenase enzyme activity, DHA), organic C and pH were monitored. The sandy loam soil, which was relatively high in organic C, did not experience increases in DHA due to organic amendments while compost produced higher DHA than manure or fertilizer treatments to the silty clay soil. There was no treatment effect on soil organic C in the sandy loam, while organic treatments increased organic C in the silty clay soil. Soil pH was affected by treatments to both soils with compost amendments producing the greatest increases in this parameter. The results emphasize the importance of considering initial soil organic C and soil texture when planning studies of the effect of organic amendments on soil microbial activity.