Granular phosphorus (P) fertilizers are often treated with coatings, such as oil or wax, to decrease dust production during packaging, shipping, storage, and spreading. Unconfirmed reports from the field suggest these coatings may negatively impact plant response to applied P fertilizers. A three-phase study was conducted in Montana, USA to determine if these coatings significantly affect P dissolution rates, soil P test levels, P uptake, or yield. Coated and uncoated monoammonium phosphate granules were obtained from two fertilizer manufacturers. In Phase I, fertilizer dissolution rates in water were measured for fertilizer application rates representing both irrigated and dryland conditions. In Phase II, dissolution rates were evaluated in an acid-washed sand at two moisture contents. In Phase III, Olsen P, P uptake, and dry biomass in maize ( Zea mays) were measured in a low pH and high pH soil for both broadcast and incorporated fertilizer applications. Dust control coatings did not significantly decrease dissolution rates, Olsen P levels, P uptake amounts, or biomass for any of the treatments or at any time. In a small percentage of comparisons, coatings significantly increased solubility, Olsen P levels, P uptake, or biomass; although, in general, coatings caused no significant differences in these parameters.
