Applicability of biochemical indices to quality assessmnet of soil pulluted with heavy metals

The objective of this study has been to test a series of soil quality biochemical indices so as to select the one(s) that would mainly rely on enzymes participating in the processes of carbon and nitrogen transformations and reflect objectively the quality of soil. Moreover, an ideal index should be comparable to yields of crops. A vegetative experiment with 5 replications was set up on two soils: loamy sand and sandy loam, which had been polluted with cadmium, copper and zinc. Once the soil moisture content was raised to the level of 60% capillary water retention capacity, the following plants were sown: oat, spring oilseed rape and yellow lupine. Twice during the growing season, the activity of soil enzymes such as dehydrogenases, catalase, urease, ß-glucosidase, acid phosphatase, alkaline phosphatase and arylsulphatase was determined. Next, based on the soil enzymatic activity as well as the content of clay and organic carbon, 21 indices of the biochemical soil activity (BA1 to BA21) were proposed, which were divided into two groups: simple and complex ones. In addition, coefficients of correlation between yields of plants and biochemical soil quality indices were calculated. The experiment has demonstrated that the activity of enzymes should be expressed in units of the product of a catalyzed reaction in 1 h time calculated per 1 kg d.m. of soil, i.e. the activity of dehydrogenases in ìmol TFF, catalase – mol O2, alkaline phosphatase and arylsulphatase – mmol PNP, while that of urease in mmol N-NH4 +. Introduction of uniform units facilitates comparison of the results and quality assessment of different soils, irrespective of the author or research centre they originate from. It has also been shown that among the 21 tested biochemical indices of soil quality assessment, the best ones are BA20 = %C × (Deh + Pal + Pac + Ure), derived from the content of organic carbon and activity of four enzymes: dehydrogenase, alkaline phosphatase, acid phosphatase and urease, and BA21 = Deh + Kat + Pal + Pac + Ure + Glu + Aryl, calculated from the activity of seven enzymes: dehydrogenases (Deh), catalase (Cat), acid phosphatase (Pac), alkaline phosphatase (Pal), urease (Ure), β-glucosidase (glu) and arylsulphatase (Aryl).