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

The effects of atrazine, carbaryl, glyphosate and paraquat on the activity of jack bean urease, free in solution or immobilized on a clean clay (montmorillonite), an organic compound (tannic acid) or a synthetic 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 laboratory conditions. Urease was affected by pesticides to different degrees, depending on its physical state, i.e. if free, immobilized or as total activity in soils or soil extracts. Glyphosate and paraquat enhanced 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 activity of jack bean urease, either free in solution or absorbed on montmorillonite. Similarly, no influence on the activity of urease immobilized on synthetic organo-mineral complexes was observed with paraquat. Since atrazine and carbaryl, which have low solubility in water, were applied in methanol, the effect of this solvent on urease activity was investigated. The activity of urease in soils and soil extracts was strongly 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 reduced the increasing effect of methanol. Free and immobilized urease were generally inhibited by methanol and both pesticides (on average -40%), but the extent of inhibition greatly depended on the nature of immobilizing support.