A new core-inhibitor coated urea that increases wheat yield and nitrogen use efficiency by reducing nitrogen loss and regulating soil nitrogen supply

Context

Escalating demographic and environmental constraints demand enhanced crop productivity with reduced ecological footprints in agriculture. Consequently, coated fertilizers and inhibitors have gained widespread adoption. Nevertheless, coated fertilizers demonstrate imprecise nutrient release profiles, whereas inhibitors exhibit constrained functional persistence and pronounced environmental susceptibility. Current studies on integrated application of coated fertilizers with inhibitors remain insufficient and require systematic evaluation.

Objectives

To develop a novel fertilizer (core-inhibitor coated urea, CICU) enabling synchronized slow-release of nitrogen (N) and inhibitors. To elucidate underlying mechanisms of yield and nitrogen use efficiency (NUE) enhancement through synchronized N-inhibitor release, and to assess its economic benefits.

Methods

The CICU was prepared by proportionally blending powdered urea, the urease inhibitor hydroquinone (HQ), and the nitrification inhibitor dicyandiamide (DCD) into granules, followed by epoxy resin coating. Preparation parameters were optimized based on an interactive test of response. The surface morphology and release characteristics of CICU were evaluated through laboratory experiments, followed by concurrent field experiments in fields in Tai’an (yield level of 6000 kg·hm⁻²) and Zibo (yield level of 7500 kg·hm⁻²), China. Seven experimental treatments were established: CK (no N fertilizer), U (normal urea), CU (epoxy resin coated urea), CHDU (epoxy-coated urea with surface sprayed HQ and DCD), IFU (agglomerated urea with novel inorganic material), HDIFU (agglomerated urea with HQ, DCD and novel inorganic material), and CHDIFU (HDIFU coated with epoxy resin).

Results

Scanning electron microscopy and hydrostatic release tests reveal a uniform distribution of urea and inhibitors in CHDIFU, with good binding of the membrane shell to the granule core, and a controlled release period of 58 days for N and 46 days for HQ and DCD with a 5 % coating. Similarity factors reveal the N-inhibitor release synchronicity in CHDIFU outperformed than CHDU (f2 = 66.38 vs. 34.14). Compared with CU, soil incubation tests reveal CHDIFU reduces ammonia volatilization by 24.95 % and N leaching losses by 16.2 %. Field experiments demonstrated that CHDIFU's inhibition of urease, hydroxylamine reductase, and nitrate reductase persisted until flowering, resulting in 25.39 %-33.14 % higher soil NO₃⁻-N and 14.67 %-23.27 % higher NH₄⁺-N versus CHDU. Compared to CHDU, CHDIFU increased post-anthesis dry matter accumulation by 8.62–11.57 % and N accumulation contribution to grains by 7.99–18.04 %, ultimately elevating yield and N fertilizer apparent utilization efficiency by 8.82 %-12.09 % and 16.91 %-26.24 %, respectively. Cost-benefit analysis showed a 57.84 $·ha⁻¹ fertilization cost increase for CHDIFU over CU, but net benefits rose by 174.83–466.04 $·ha⁻¹.

Conclusions

The granulation-coating approach enables prolonged inhibitor efficacy and synergistic N-inhibitor release. Through sustained regulation of N release and transformation, CICU mitigates ammonia volatilization and N leaching while enhancing soil N supply-crop demand synchronization, thereby elevating grain yield and NUE. Although CHDIFU incurs higher production costs than CU and CHDU, its viability is evidenced by reduced environmental remediation expenditures and enhanced net profitability. Consequently, CICU application with precision N management represents a viable strategy for sustainable agriculture.