Thermal stabilities of urease enzymes in some irish soils

The thermal stabilities of urease enzymes in six re-wetted, air-dry soils were characterized and compared by incubation at 4, 37 and 70°C. Inactivation rates were dependent on temperature and soil type. Calculated half-lives (t_1/2 values) of soil urease were 384-768 h at 4°C, 79-229 h at 37°C and <2-6 h at 70°C. At 37°C, soil urease decay patterns were best described by first-order kinetics. Half-life values (t_1/2) at 37°C were significantly correlated with soil pH values (r = 0.944; P < 0.05) but less strongly with organic-C (r = 0.699; NS) and CEC (r = 0.671; NS). Almost all (98.9%; P < 0.05) of the variation in t_1/2 values was accounted for by a multiple regression equation incorporating the foregoing variables.