Nitrogen Losses from Urea as Affected by Altering Soil Urease Activity

Laboratory incubation experiments were conducted to determine whether nitrogen losses from urea could be reduced by manipulating the urease activity of the soil. The natural urease activity of Chalmers silt loam and Plainfield sand was modified directly by applications of either additional urease enzyme or an enzyme inhibitor and indirectly by applications of a decomposing mulch and liming material. Additional urease enzyme increased the rate of urea hydrolysis, the rate of ammonia volatilization during the early part of the incubation period, and also the rate of nitrification during the latter part of the incubation period. The enzyme inhibitor, p ‐chloromercuribenzoate, decreased the rate of urea hydrolysis but maintained soil ammonium contents at a high level throughout the entire incubation period due to inhibition of nitrification. Treatments had no significant effect on total volatile ammonia losses. The presence of a corn mulch layer ( Zea mays ) in the zone of urea application increased urea hydrolysis rates only when the mulch was undergoing rapid decomposition. The mulch layer increased initial rates of ammonia volatilization but reduced leaching losses of nitrogen significantly. Significantly lower volatile ammonia losses were observed when lime and urea were applied together on the surface of a corn mulch than when they were applied to bare soil.