Preparation, characterization, and performance evaluation of a controlled-release inhibitor-enhanced nitrogen...

Improving nitrogen fertilizer use efficiency while reducing nitrogen losses is a major challenge for sustainable crop production. In this study, a controlled-release inhibitor-enhanced nitrogen fertilizer (CYRF) was developed by integrating a polyurethane controlled-release membrane with a 3,4-dimethylpyrazole phosphate (DMPP) nitrification-inhibitor layer. Its structural characteristics, nutrient release behavior, and nitrogen-regulating performance were evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, static water incubation, soil incubation at different temperatures and field nitrogen-15 (¹⁵N) tracing. Morphological and elemental analyses confirmed that CYRF possessed a distinct multilayer structure consisting of an outer controlled-release membrane and an inner DMPP-containing inhibitor layer, providing a structural basis for the coordinated release of urea nitrogen and DMPP. Under static water incubation at 25 °C, the cumulative release of urea nitrogen increased from 0.40% at 7 d to 87.50% at 98 d, while DMPP release increased from 0.70% to 79.00% over the same period. DMPP was released slightly earlier than urea nitrogen during the 21-49 d incubation period, and their cumulative release rates were strongly positively correlated (r = 0.975, P < 0.001). Soil incubation showed that CYRF consistently enhanced ammonium nitrogen retention while suppressing nitrate nitrogen accumulation across different temperatures. Compared with the controlled-release fertilizer (CRF), CYRF increased ammonium nitrogen retention by 37.3% and reduced nitrate nitrogen accumulation by 16.4% at 15 °C. At 25 °C, CYRF reduced nitrate nitrogen accumulation by 97.0-98.7% during the 50-90 d incubation period, while at 35 °C it decreased nitrate nitrogen accumulation by 42.0%. Field ¹⁵N tracing further showed that, compared with CRF(¹⁵N), CYRF(¹⁵N) significantly increased ¹⁵N utilization rates by 14.60 and 5.30 percentage points and reduced nitrogen loss rates by 11.45 and 11.11 percentage points in winter wheat and summer maize, respectively. Overall, CYRF effectively synchronized controlled nitrogen release with nitrification inhibition, providing a promising strategy for improving nitrogen use efficiency and reducing nitrogen losses in agricultural production.