Changes in enzyme activities and microbial biomass of tallgrass prairie soil as related to burning and nitrogen fertilization

Microbial biomass and enzyme activities are affected by management practice s and can be used as sensitive indicators of ecological stability. Microbia l biomass C (MBC), microbial biomass N (MBN) and eight enzyme activities in volved in the cycling of C, N, P and S were studied in the surface (0-5 cm) of an Irwin silty clay loam soil (fine, mixed, mesic, Pachic Arguistoll) i n a tallgrass prairie ecosystem. Treatments of annual spring burning and N fertilization were initiated in 1986 and encompassed: (1) unburned-unfertil ized, (2) burned-unfertilized, (3) burned-fertilized, and (3) unburned-fert ilized, Activities of dehydrogenase, beta-glucosidase, urease, deaminase, d enitrifying enzyme, acid phosphatase, alkaline phosphatase, and arylsulfata se were assayed. Long-term burning and N fertilization of the tallgrass pra irie soil reduced MBC and MBN relative to the unburned-unfertilized treatme nt. The effects of burning and N fertilization varied among the enzymes and the time of sampling. Long-term burning significantly (P < 0.05) increased activities of urease and acid phosphatase, but decreased activities of bet a-glucosidase, deaminase and alkaline phosphatase. Long-term N fertilizatio n significantly increased activities of beta-glucosidase and acid phosphata se but decreased urease activity. This study found that several soil enzyme activities can be used as indicators of ecological changes caused by N fer tilization and long-term burning management practices. The relevance of the se changes in surface soil to the long-term sustainability of this ecosyste m needs further evaluation. (C) 1999 Elsevier Science Ltd. All rights reser ved.