Turnover of Urea in a Soil from the North China Plain as Affected by the Urease Inhibitor NBPT and Wheat Straw

In the North China Plain (NCP), urea is applied to predominantly high-pH soils and high gaseous losses of N are observed in the forms of ammonia (NH3) and nitrous oxide (N2O). The production of N2O and N2 is further stimulated by the addition of fresh organic materials. The urease inhibitor (UI) N-(n-butyl) thiophosphoric triamide (NBPT) restricts the loss of N by reducing the rate of urea hydrolysis and limiting the substrates for NH3 and N2O emission. We investigated the turnover of N—as well as the emissions of NH3, N2O and CO2—as affected by the addition of wheat straw and urea +NBPT in an incubation experiment using soil from a farmer’s field, typical for the NCP. Added wheat straw prolonged the persistence of NH4+ after the application of both urea and urea +NBPT, while reducing the formation of nitrate. Wheat straw may therefore either act as a stimulant of hydrolysis or as an inhibitor of nitrification. Urea increased soil respiration and the emission of N2O, possibly acting as a primer for microbial activity as described in earlier studies. In combination with the application of organic C sources, this effect of urea may be a main driver of gaseous N loss.