How Do NPK-Organomineral Fertilizers Affect the Soil Availability and Uptake of Iron, Manganese, Copper, and Zinc by Maize Cultivated in Red and Yellow Oxisols?

Micronutrient availability is low in Oxisols. Additionally, organic compounds in organomineral fertilizers (OMFs) used as a source of nitrogen (N), phosphorus (P), and potassium (K) may interact with metallic micronutrients in the soil, altering their dynamics and availability to crops. Therefore, the aim of this study was to assess the effects of NPK-OMFs, produced by composting mixtures of organic residues (chicken manure and coffee husk) and monoammonium phosphate (MAP), on the dynamics of iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in the soil. The study also aimed to examine the availability and uptake of these micronutrients by maize cultivated in Oxisols. NPK-OMFs were produced using various proportions of organic residues and MAP. The availability of Fe, Mn, Cu, and Zn from OMFs was determined in both whole soil and solution during maize cultivation under greenhouse conditions in Red and Yellow Oxisols, which had contrasting soil organic matter (SOM) contents. Additionally, the release rate of micronutrients was evaluated in incubated soil-OMF mixtures. Higher proportions of organic residues in OMFs decreased the Mn content in the soil solution of Oxisols. It increased Fe and Cu levels in the Oxisol with higher SOM, but reduced Fe levels in the Oxisol with the lowest SOM level. In all Oxisols, OMFs with higher organic residues enhanced the availability of Zn. In the SOM-poor Oxisol, biomass, Fe, and Mn increased in the maize shoot. The use of NPK-OMFs alters the dynamics and improves the use efficiency, significantly affecting the availability of Mn, Zn, and Fe in the soil solution and, to a lesser extent, in the whole Oxisols compared to mineral fertilizers.