PREPARATION OF FERTILIZERS WITH ROSIN AND TRICALCIUM PHOSPHATE COATEDZINC CHELATES - LABORATORY CHARACTERIZATION

Zinc fertilizers were obtained by adhering Zn-EDTA or Zn-lignosulfonat e over urea pellets of 1.6-2 mm diameter, to give a span of zinc weigh t percentages between 0.60 and 1.40. Some of these pellets were also c oated. The materials used as adhesives and coatings were mixtures of r osins (natural, dismutated, and esterified) and tricalcium phosphate. The weight percentages of coatings ranged from 0 to 47%. Water solubil ity kinetics showed that zinc solubilization in the base products (unc oated) were almost immediate, while the percentage released in the coa ted products diminished as the coating thicknesses were increased, up to 63 and 14% for the more heavily coated products of Zn-EDTA and Zn-l ignosulfonate, respectively. Equations were established that enabled t he behavior of products with the same percentage of coating in the two series to be predicted and compared. The tested products comply with national and international standards for commercial fertilizers with r egard to their chemical composition. Their physical properties were wi thin the Limits found with commercial fertilizers. A scanning electron microscopy study showed that the rosin coatings were fairly compact a nd homogeneous.