Evaluation of Controlled Release Urea on the Dynamics of Nitrate, Ammonium, and Its Nitrogen Release in Black Soils of Northeast China

Controlled release urea (CRU) is considered to enhance crop yields while alleviating negative environmental problems caused by the hazardous gas emissions that are associated with high concentrations of ammonium (NH₄⁺) and nitrate (NO₃-) in black soils. Short-term effects of sulfur-coated urea (SCU) and polyurethane-coated urea (PCU), compared with conventional urea, on NO₃- and NH₄⁺ in black soils were studied through the buried bag experiment conducted in an artificial climate chamber. We also investigated nitrogen (N) release kinetics of CRU and correlations between the cumulative N release rate and concentrations of NO₃- and NH₄⁺. CRU can reduce concentrations of NO₃- and NH₄⁺, and PCU was more effective in maintaining lower soil NO₃-/NH₄⁺ ratios than SCU and U. Parabolic equation could describe the kinetics of NO₃- and NH₄⁺ treated with PCU. The Elovich equation could describe the kinetics of NO₃- and NH₄⁺ treated with SCU. The binary linear regression model was established to predict N release from PCU because of significant correlations between the cumulative N release rate and concentrations of NO₃- and NH₄⁺. These results provided a methodology and data support for characterizing and predicting the N release from PCU in black soils.