Synergistic Effect of Urea·Gallic Acid Cocrystal for Sustained Nitrogen Release and Plant Growth Enhancement

Urea as a fertilizer suffers from its higher water solubility, leading to low nitrogen use efficiency (NUE), environmental pollution, and reduced agricultural productivity. In this study, we developed a novel urea-based cocrystal system, the urea·gallic acid 1:1 cocrystal (UGA), using a mechanochemical synthesis approach, designed for sustained release of nitrogen. The UGA synthesized was assessed for its solubility, hydration stability, nitrogen release behavior, and bioavailability under glasshouse conditions. UGA exhibited exceptional hydration stability and low solubility (34.1 mg/mL) compared with conventional urea. Slow-release behavior of UGA was associated with a 2.5-fold reduction in nitrogen emissions, as observed in soil column experiments. Bioavailability studies demonstrated that all fertilized treatments significantly improved Solanum lycopersicum growth (P < 0.01). Shoot elongation increased by 28% (urea), 23% (UGA), and 20% (half-dose UGA), while UGA enhanced root growth by 42% (P = 0.04). Shoot and root dry weight increased by 214 and 228%, respectively (P < 0.001). UGA-treated plants also exhibited enhanced nitrogen uptake, with the highest N uptake efficiency observed at half-dose UGA treatment. These findings highlight UGA’s potential as a slow-release nitrogen fertilizer to significantly impact global food production by enhancing NUE and minimizing environmental pollution, contributing to a more sustainable agriculture.