ACTIVITY OF FREE AND IMMOBILIZED UREASE IN SOIL - EFFECTS OF PESTICIDES

The effects of atrazine, carbaryl, glyphosate and paraquat on the acti vity of jack bean urease, free in solution or immobilized on a clean c lay (montmorillonite), an organic compound (tannic acid) or a syntheti c organo-mineral [Al(OH)x-tannate and Al(OH)x-tannate-montmorillonite] complexes were studied. For comparison, pesticide influence on urease activity in some soils and soil extracts was investigated, under labo ratory conditions. Urease was affected by pesticides to different degr ees, depending on its physical state, i.e. if free, immobilized or as total activity in soils or soil extracts. Glyphosate and paraquat enha nced the urease activity of soils (by 1.1-1.4-fold) and soil extracts (by 2.59-6.73-fold). No significant effects were detected on the activ ity of jack bean urease, either free in solution or absorbed on montmo rillonite. Similarly, no influence on the activity of urease immobiliz ed on synthetic organo-mineral complexes was observed with paraquat. S ince atrazine and carbaryl, which have low solubility in water, were a pplied in methanol, the effect of this solvent on urease activity was investigated. The activity of urease in soils and soil extracts was st rongly increased by methanol (by 1.48-7.47-fold and by 1.42-11.62-fold , respectively) and carbaryl (by 1.73-2.91-fold). Atrazine partly redu ced the increasing effect of methanol. Free and immobilized urease wer e generally inhibited by methanol and both pesticides (on average -40% ), but the extent of inhibition greatly depended on the nature of immo bilizing support.