DENITRIFICATION AS A MEASURE OF SOIL BIOL OGICAL-ACTIVITY

Biological denitrification is the microbial dissimilative reduction of nitrates or nitrites to produce gaseous nitrous oxide arid elemental nitrogen. As reported by some authors (T i e d j e et al., 1984), the ability to denitrify is a property very much spread among soil microor ganisms. For this reason and for the general importance of denitrifica tion in the soil nitrogen cycle, denitrification activity (or any othe r characteristics of denitrification) can be considered as an importan t soil biological parameter. The present contribution summarizes the p rinciples of the determination of denitrification. Two methods of meas uring denitrification activity are described in detail: the method of inhibition of N2O reduction by acetylene (acetylene inhibition method) and the method of reduction of added N2O. Results of denitrification measurement by the acetylene inhibition method in soil cores, taken fr om three stages of a secondary succession on entric cambisol, are pres ented. It follows from the results given in Tab. I, that there is a ma rked seasonal variability of denitrification activity - the highest va lues were recorded in spring. A high general variability of the result s, expressed by variation coefficients, is also evident. This denitrif ication activity represents a certain actual soil parameter which is s trongly influenced by environmental factors and characterized by consi derably high space heterogeneity. Furthermore, results of denitrificat ion activity measurement in soil layers of mollisol in samples in the form of sieved and homogenized soil, incubated under partly optimized conditions (preincubation, glucose addition), are presented. Denitrifi cation was measured simultaneously using two different techniques: ace tylene inhibition method and method of the reduction of N2O added. Bot h methods gave similar results (Tab. II). The highest denitrification activity was found in the surface layer 0 to 4 cm, and it decreased wi th the depth. A significantly lower variability of the results is appa rent in comparison with the results presented in Tab. I. Data on the d enitrification activity measured under optimum conditions reflect die suitability or unsuitability of various environmental and soil conditi ons for denitrifiers and denitrification on the site prior to sampling . It was concluded that the measurement of denitrification enzyme acti vity - the DEA method (T i e d j e et al., 1989) should be a suitable method for quantification of denitrification as a microbial soil param eter. Using this method all three most important conditions of denitri fication are optimized: pO2, nitrate and carbon. This possibility is t o be verified.