Multifunctional Urea Cocrystal with Combined Ureolysis and Nitrification Inhibiting Capabilities for Enhanced Nitrogen Management

Abstract

The novel ternary Zn(II)-thiourea–urea ionic cocrystal [Zn(thiourea)(urea)Cl₂], (ZnTU) has been prepared by both solution and mechanochemical processes and structurally characterized by solid-state methods. ZnTU exhibited improved response properties to water as relative humidity as inherited from thiourea. The results of enzymatic activity measurements provide evidence that ZnTU is effective in modulating urea hydrolysis both in vitro (negatively impacting on the activity of isolated urease) and in vivo (decreasing the ureolytic activity of Sporosarcina pasteurii, a widespread soil bacterium), and that Zn(II) is the component of the cocrystal acting as the actual urease inhibitor. Concomitantly, the analysis of the ammonia monooxygenase (AMO) enzymatic activity in Nitrosomonas europaea, taken as a representative of soil ammonia-oxidizing bacteria, in the presence of ZnTU reveals that thiourea is the only component of ZnTU able to inhibit ammonia conversion to nitrite. It has also been shown that ZnTU maintains these capabilities when applied to bacterial cultures containing both S. pasteurii and N. europaea working in tandem. The compound can thus act both as a fertilizer via urea and via the Zn(II) and thiourea components, as a dual action inhibitor of the activities of the enzymes urease and AMO, which are responsible for the negative environmental and economic impact of the agricultural use of urea as soil fertilizer. These results indicate that ZnTU should be considered a novel material to improve N fertilization efficiency, toward a more environment-friendly agricultural practice.