Humic Acid Improves Zn Fertilization in Oxisols Successively Cultivated with Maize-Brachiaria

Zinc (Zn) is an essential micronutrient for plant growth, and Zn deficiency is a global issue, especially in tropical soils. This study aimed to investigate the effects of humic acid (HA) and the Zn addition (Zn sulfate + HA) on the growth of maize and brachiaria in two contrasting Oxisols. The potential complexation of Zn sulfate by HA was evaluated by Fourier-transform infrared (FTIR) spectroscopy analysis. Zinc content and its availability in solution and the shoot and root biomass of maize and brachiaria were determined. FTIR spectroscopy revealed the complexation of Zn sulfate by HA through its S and C functional groups. In both Oxisols, solution Zn increased due to the combined use of Zn and HA. In a soil type-dependent manner, maize biomass and Zn in its shoots were affected only by the exclusive use of Zn fertilization. In the Yellow Oxisol, brachiaria growth and Zn accumulated in its shoot were positively affected by the combined use of Zn fertilization with HA. In the Oxisol with lower organic matter content, HA can assure adequate supplying of residual Zn, while increasing growth of brachiaria cultivated in sequence to maize.

Exposure to Weathered and Fresh Nanoparticle and Ionic Zn in Soil Promotes Grain Yield and Modulates Nutrient Acquisition in Wheat ( Triticum aestivum L.)

This study evaluated weathered and fresh ZnO-nanoparticles and Zn-salt effects on nutrient acquisition and redistribution in wheat. Weathered and fresh ZnO-nanoparticles and Zn-salt significantly increased grain yield by 15% and 29%, respectively. Postharvest soil acidification indicated ZnO-nanoparticles dissolved during growth. Zn was significantly bioaccumulated from both Zn types, but with low root-to-shoot bioaccumulation efficiency: 24% and 20% for weathered nanoparticles and salt, and 48% and 30% for fresh nanoparticles and salt. Grain Zn content was increased 186% and 229% by weathered nanoparticles and salt, and 229% and 300% by fresh nanoparticles and salt. Shoot-to-grain translocation efficiency was high: 167% and 177% for weathered nanoparticles and salt, and 209% and 155% for fresh nanoparticles and salt. However, Zincon assay indicated grain Zn does not exist as ions. This study demonstrates that ZnO-nanoparticles and Zn-salt vary in their effects on nutrient acquisition in wheat, with relevance for biofortification of Zn for human nutrition.