Hydrophobic coatings for granular fertilizers to improve physical handling and nutrient delivery

Abstract

Globally, fertilizer agglomeration (caking) during transport and storage leads to irreversible breakdown, dust, equipment blockages and inconsistent field application. Coatings which are hydrophobic reduce moisture uptake at high humidity and reduce caking but still need to release plant nutrients. Here, natural and synthetic waxes coated onto fertilizer granules with powders to impart surface roughness reduced contact between condensed water droplets and the surface, lowering moisture ingress. The adhesive strength of the coatings and rate of nutrient release are shown with degree of roughness quantified using laser surface microscopy. The wax-only coatings on potassium chloride fertilizer (MOP, 50% K) reduced moisture uptake by up to 30%, while for coatings with wax and roughener reductions were between 56% and 80%. Beeswax with micronutrient rougheners reduced moisture uptake by over 65% whilst maintaining uninterrupted nutrient supply. Thus, these hydrophobic coatings can improve physical characteristics of fertilizer without compromising the kinetics of nutrient release.