Application of soil enzyme activity test kit in a field experiment

We developed a test kit utilizing fluorogenic substrate analogues for the measurement of several enzyme activities in soil samples. Our hypothesis was that the pattern of different enzyme activities reflects changes in microbial structure and activity in a more sensitive way than total microbial biomass or activities of individual enzymes. In the test kit activities of 11 soil enzymes were measured simultaneously from diluted soil slurries on multiwell plates. After incubation for 3 h the fluorescence was measured quantitatively using an automated plate reader. The test kit was evaluated in a field experiment designed to investigate various management practices. During the years 1981–1993 the experimental field was divided into four sites. One of the plots received full mineral fertilization on the basis of chemical soil analysis, another received 50% of the recommended mineral fertilization, the third plot received green manure (harvested crop residues) and the fourth plot received composted crop residues. Since 1994 the sampling area included sites in a transitional stage to organic cultivation and the minerally fertilized site. Season, crop plant and management practice all gave rise to differences in the enzyme activity profile. The fluorogenic analysis was sensitive and allowed quantification of all the enzyme activities in all the samples. When four replicate measurements were used the standard deviation was usually less than 10%, depending on the enzyme.