Effect of urease/nitrification inhibitors on transformation of urea-N in albic soil

Using an incubation test under a constant temperature, the effects of an urease inhibitor (NBPT), a nitrification inhibitor (DMPP), and their combined application on urea nitrogen transformation in albic soil on the Sanjiang Plain was investigated. In albic soil, the effective reaction time of NBPT is less than 13 d, which was shorter than that of brown and blank soil, and the effects of NBPT on soil ammonium, nitrate nitrogen (NO3--N) and nitrification rate were consistent with the application of urea. During the 4?7 d after the application of slow-release urea with the combination of NBPT and DMPP to the soil, NBPT effectively inhibited the activity of urea-hydrolyzing enzymes, and thus delayed the hydrolysis of urea. The inhibitory effect of DMPP on ammonium nitrogen (NH4+-N) was identical to the effect of combined application of NBPT and DMPP, which maintained a high level of soil NH4+-N for more than 80 d. DMPP can effectively inhibit the transformation from NH4+-N to NO3--N At 80 d, 54.5856.85% of the nitrogen remaining in the soil was in the form of NH4+-N, thus the nitrification rate was only about 50% and the inhibitory effect of DMPP on nitrification was significant in albic soil. Therefore, in albic soil, when using the slow-release urea with NBPT, DMPP, or a combination of NBPT and DMPP, we recommend that adding 1% DMPP to urea is the best option.