Microbial metabolic activities in soils of old-field communities following eleven years of nutrient enrichment.

Effects of 11 years (1978-1988) of nutrient enrichment (fertilizer or sludge) on microbial metabolic activity in soil samples collected from contrasting types of old-field communities were studied during September 1989. During the 1989 growing season, subplots were manipulated by tilling and/or liming to evaluate mechanisms of ecosystem recovery or were left undisturbed. Metabolic activities of soil microorganisms were determined by measuring dehydrogenase activity within soil samples collected from these subplots. The amounts of 2,3,5-triphenyltetrazolium formazan formed during incubation by the reduction of 2,3,5-triphenyltetrazolium chloride were used to evaluate dehydrogenase activity. Plots that had received long-term applications of sludge or fertilizer had significantly lower rates of microbial activity (P<0.05) than did control plots. Fertilizer and sludge plots treated with lime had significantly higher microbial metabolic activity (P<0.05) than those not receiving lime. Whereas liming stimulated microbial activity to near control levels, tilling had no significant treatment effect.