Physicochemical characterization of fertilizers containing concentrated suspensions of CuO, MnCO3 and ZnO

Abstract

The utilization of insoluble sources of micronutrients as concentrated suspensions (CSs) is increasing in Brazilian agriculture; however, much information regarding the physicochemical characterization of these products is required to demonstrate the absorption behavior by plant leaves. This study aimed to characterize the CSs available on the Brazilian market to support their potential use as foliar fertilizers. We selected five CSs containing Mn, five CSs containing Zn and three CSs containing Cu from five different companies. In each product, the mean particle size was evaluated by dynamic light scattering (DLS), the particle shape and size were evaluated by scanning electron microscopy (SEM), the aggregation degree was determined by the zeta potential and the heavy metal contents were determined by acid digestion followed by reading on ICP-OES. The mean hydrodynamic diameter of fertilizers containing Cu, Mn and Zn was 315 ± 55, 378 ± 184 and 435 ± 107 nm, respectively. The zeta potential varied from –20 to –30 mV, indicating potential particle aggregation and formation of higher structures. SEM images indicated great variation in the size and shape of the particles in each product. All products exhibited concentrations of toxic elements within the legislation thresholds. The average particle size of CSs currently marketable in Brazil does not allow their classification as nanomaterials (< 100 nm). Therefore, their foliar absorption is unlikely, once the particle size is higher than the exclusion limit observed for stomata and cuticle pathways, as well as the nutrient content as ions is low according to the solubility constant.