The metabolic activity of soil microorganisms is essential for organic matter turnover. The metabolization and immobilization of inorganic nutrients and trace elements are also mainly a result of microbial activities. Metabolic activities are determined by the species composition, which in turn is influenced by the available litter, the soil type and other environmental conditions. Special enzymes catalyze the organic matter turnover. These enzymes are produced by the organisms and act intra- or extracellularly. Soil enzymes include a wide spectrum of oxidoreductases, transferases, hydrolases and lyases. Soil enzymes are mainly of bacterial and fungal origin. Only a small fraction is excreted by plants and/ or animal. The dehydrogenase activity of a soil is thus the result of the activity of different dehydrogenases, which are an important component of the enzyme system of all microorganisms. Actual and potential dehydrogenase activities were determined in the 0-20, 20-40 and 40-60 cm layers of a brown luvic soil submitted to a complex tillage, crop rotation and fertilisation experiment. Dehydrogenase activities in both non-tilled and conventionally tilled soil under all crops of both rotations decreased with increasing sampling depth. It was found that no-till - in comparison with conventional tillage - resulted in significantly higher soil enzymatic activities in the 0-20 cm layer and in significantly lower activities in the deeper layers. The soil under maize or wheat was more enzyme-active in the 6-than in the 2-crop rotation. In the 2-crop rotation, higher enzymatic activities were registered under wheat that under maize.In the 6- crop rotation, the enzymatic indicators of soil quality decreased, depending on the nature of crops and kind of fertilisers ( mineral NP or farmyard manure), in the following order: minerally fertilised (m.f) wheat ≈ m.f. oat . clover mixture >farmyard manured maize > m.f. soybean > m.f. clover > m.f. maize. Farmyard manuring of maize . in comparison with its mineral (NP) fertilisation . led to a significant increase in each activity.

dehydrogenase; preluvosoil; crop rotation; fertilizers

Presentation: oral