Effect of urease inhibitors on denitrification in soil

Abstract. The influence of three urease inhibitors, hydroquinone (HQ), phenyl phosphorodiamidate (PPDA) and N-(n-butyl) phosphorothioic triamide (NBPT) on denitrification of nitrate in soil was studied in an incubation experiment under waterlogged conditions, at 25°C and in the presence of increasing amounts (0.0, 0.1 and 1 %) of ground barley straw. Two hundred milligrams of nitrate-N (as potassium nitrate) was added with the respective urease inhibitors.
Addition of barley straw increased the denitrification rate in the soil. Within 2 days the added nitrate-N was completely reduced. This result was confirmed by the measurement of nitrous oxide. HQ decreased gaseous nitrogen loss by decreasing the activity of the denitrifiers in the soil. The inhibitory effect was increased by adding increasing amounts of HQ. Because denitrification is stimulated by readily decomposable organic matter, the retardation seems to be a short-term effect. The other urease inhibitors, PPDA and NBPT, had no significant influence on the denitrification process when they were applied at the rate of 4 mg per kilogram of soil.