EFFECT OF SUBSTRATE CONCENTRATION, SOIL-MOISTURE, AND ORGANIC AMENDMENTS ON UREASE ACTIVITY OF SOIL CONTAINING VARIABLE NICKEL AMOUNTS

Effects of substrate concentration, soil moisture, and type of added organic material on urease activity of soil containing variable Ni content were studied Urease activity ranged from 7.45 to 12.66 mug N hydrolyzed g-1 soil h-1 at 37-degrees-C. Activity was higher in unpolluted than in Ni-polluted soil and increased linearly with increasing substrate concentration. It also increased with increasing moisture content up to field capacity (0.03 MPa) and decreased at flooding. Addition of wheat straw had no effect on soil urease activity, however, activity was increased with the addition of sewage sludge, pressmud, or farmyard manure. Increasing levels of farmyard manure (up to 4%) increased the urease activity of soils at all Ni concentrations, but the increase was less marked at the high Ni concentration.