Application of soil enzyme activity test kit in a field experiment

We developed a test kit utilizing fluorogenic substrate analogues for the m easurement of several enzyme activities in soil samples. Our hypothesis was that the pattern of different enzyme activities reflects changes in microb ial structure and activity in a more sensitive way than total microbial bio mass or activities of individual enzymes. In the test kit activities of 11 soil enzymes were measured simultaneously from diluted soil slurries on mul tiwell plates. After incubation for 3 h the fluorescence was measured quant itatively using an automated plate reader. The test kit was evaluated in a field experiment designed to investigate various management practices. Duri ng the years 1981-1993 the experimental field was divided into four sites. One of the plots received full mineral fertilization on the basis of chemic al soil analysis, another received 50% of the recommended mineral fertiliza tion, the third plot received green manure (harvested crop residues) and th e fourth plot received composted crop residues. Since 1994 the sampling a-r ea included sites in a transitional stage to organic cultivation and the mi nerally fertilized site. Season, crop plant and management practice all gav e rise to differences in the enzyme activity profile. The fluorogenic analy sis was sensitive and allowed quantification of all the enzyme activities i n all the samples. When four replicate measurements were used the standard deviation was usually less than 10%, depending on the enzyme. (C) 2001 Else vier Science Ltd. All rights reserved.