KINETICS OF SOIL UREASE AFFECTED BY UREASE INHIBITORS AT CONTRASTING MOISTURE REGIMES

With black soil (Pachic Udic Argiboroll) of Northeastern China as the test object, an incubation test was conducted to investigate the effects of urease inhibitors, hydroquinone (HQ), phenyl phosphorodiamidate (PPD) and N-(n-Butyl) thiophosphoric triamide (NBPT), on the kinetic characteristics of soil urease under normal moisture and waterlogged conditions, aimed to study the changes of catalytic potential of soil urease and the inhibition mechanisms. The results showed that test urease exhibited typical Michaelis-Menten kinetic behaviors, and all test inhibitors increased the Km and decreased the Vmax of soil urease, behaving as mixed inhibitors to soil urease. Under both normal and waterlogged conditions, compared with HQ, PPD and NBPT made Km increase and Vmax and Vmax/Km decrease more greatly, and the duration of these effects was longer (ca. 30 days vs. 10 days). Under water-logging, PPD made more increment of Km and more decrement of Vmax and Vmax/Km than NBPT, compared with that under normal soil moisture condition, suggesting that NBPT was more available under normal soil moisture condition, while PPD was promising under water-logging condition. To apply urease inhibitors and to control soil moisture condition could be a feasible way in increasing fertilizer N use efficiency affected by soil urease.