Zinc Oxide-Based Fertilizers are Better Foliar Sources of Zinc than Zinc Sulfate for the Growth of Common Bean

Zinc (Zn) deficiency limits common bean (Phaseolus vulgaris L.) production and quality. We evaluated foliar applications of zinc sulfate (ZnSO4) and zinc oxide (ZnO) - based fertilizers (nano - zinc oxide, ZINTRAC (TM), and Maxi Zinc (R)), at 2, 4, or 6 mg per plant in hydroponically grown common bean. A negative (no Zn supply) and a positive control (Zn supply via roots) were included as treatments. The nano - zinc oxide did not reach nanoscale dimensions and performed similarly to ZINTRAC (TM) and Maxi Zinc (R). Notably, ZnO - based fertilizers outperformed ZnSO4 in enhancing pod biomass and shoot Zn concentration. The highest shoot Zn concentrations were observed with 6 mg Zn per plant of nano - ZnO, ZINTRAC (TM), and Maxi Zinc (R). Also, agronomic efficiency index (AEI) and applied Zn recovery (AZnR) indicated that ZnO - based fertilizers were a better foliar Zn source than ZnSO4 for the growth of common bean. The highest AEI was observed with 6 mg Zn per plant of nano - ZnO, ZINTRAC (TM), and Maxi Zinc (R). These findings support the recommendation of ZnO - based fertilizers over ZnSO4 for foliar Zn supply in common bean, but further research is needed to pinpoint the optimal foliar Zn dose for maximizing common bean growth.