Objectives The combined use of urease and nitrification inhibitors with urea can improve crop yield and nitrogen use efficiency (NUE). However, the effectiveness of inhibitors is often limited by environmental factors, preventing them from achieving their maximum benefits. This study aimed to develop a novel stabilized nitrogen fertilizer that can fully utilize the potential of inhibitors, evaluate its slow-release properties, and assess its effects on plant growth, yield, quality, and soil nitrogen supply capacity. The research provides technical and theoretical support for the development of new stabilized fertilizers.

Methods Urease inhibitor (hydroquinone, HQ) and nitrification inhibitor (dicyandiamide, DCD) were dissolved in 75% ethanol and sprayed onto the surface of inorganic fiber particles, which were then dried at 45℃ overnight. The particles were mixed with urea to prepare a novel stabilized nitrogen fertilizer−inorganic fiber particles carrying inhibitor mixed with urea (MHDU). The microstructure and slow-release properties of MHDU were evaluated using scanning electron microscopy and soil column leaching experiments. The residence time of inhibitors in the soil was determined using the soil column leaching method. A field experiment was conducted with five fertilization treatments: no nitrogen fertilizer (CK), urea alone (U), HQ + DCD + urea (HDU), inorganic fiber particles + urea (MU), and MHDU. The effects of each treatment on pepper growth, yield, quality, NUE, and soil nitrogen supply capacity were compared.

Results The inorganic fiber particles were composed of interwoven filamentous fibers of varying thicknesses, with HQ and DCD uniformly attached to the fiber surfaces. On the 1st and 6th days of the soil column incubation, the leaching amounts of inhibitors in the MHDU treatment were significantly lower than those in the HDU treatment, with HQ reduced by 40.62% and 77.28%, and DCD reduced by 51.14% and 34.94%, respectively. From the 11th to the 31st day of incubation, no inhibitors were leached in the HDU treatment, whereas the MHDU treatment showed HQ leaching of 0.70−1.48 mg and DCD leaching of 1.26−11.18 mg, indicating that the slow-release inhibitor particles extended the residence time of inhibitors in the soil to 31 days. The leaching amount of soil inorganic nitrogen in the MHDU treatment was significantly reduced by 22.47%, 6.65%, and 14.79% compared to the U, HDU, and MU treatments, respectively. Compared to the U, HDU and MU treatments, the MHDU treatment reduced plant height by 8.96%−15.05%, increased stem diameter by 27.64%−29.39%, MHDU treatment significantly increased yield by 21.59%−39.88%, compared to the U, HDU, and MU treatments, and effectively improved the soluble protein and vitamin C contents in peppers. The soluble protein increased by 30.86%−39.04% compared to the U, HDU, and MU treatments, the vitamin C content increased by 23.53%−24.02% compared to the HDU and MU treatments. The MHDU treatment resulted in the highest plant nitrogen accumulation, NUE, and apparent nitrogen fertilizer recovery efficiency, which were significantly increased by 23.11%, 39.88%, and 68.97%, respectively, compared to the U treatment. Compared to the MU treatment, the MHDU treatment significantly reduced soil urease activity during the seedling and initial flowering stages. Compared to the HDU and MU treatments, the MHDU treatment increased soil ammonium nitrogen content during the fruiting and peak fruiting stages and reduced soil nitrate nitrogen content throughout the entire growth period. In the U, HDU, and MU treatments, soil ammonium and nitrate nitrogen contents were significantly positively correlated with soil urease activity, whereas no significant correlation was observed in the MHDU treatment.

Conclusion By uniformly attaching the inhibitors HQ and DCD to the surfaces of interwoven filamentous fibers, direct contact between the inhibitors and the soil was effectively avoided, and the sustained release of inhibitors was extended to 31 days. When mixed with urea to form the inorganic fiber particles carrying inhibitor mixed with urea (MHDU) and applied to the soil, it suppressed soil urease activity in the early growth stages, maintained high inorganic nitrogen content in soil during the fruiting and peak fruiting stages, promoted nitrogen supply during the reproductive phase of peppers, and ultimately significantly improved pepper yield, quality, and nitrogen fertilizer efficiency. Therefore, the inorganic fiber-adsorbed stabilized nitrogen fertilizer is more effective in synchronizing fertilizer nutrient release with crop uptake.