In Brazilian legislation, the control for micronutrient concentrations in mineral fertilizers considers the total content. As a consequence, low-cost by-products and even industrial residues are generally used as a source for micronutrients, despite their low availability to plants. To evaluate fertilizer solubilities, water, citric acid 20 g L-1, and neutral ammonium citrate (1 + 9) extracting solutions were applied to mixtures containing micronutrients. The same study was realized for micronutrient sources. Results were similar for both sources and mixtures. Citric acid solution 20 g L-1 was the most promising option to evaluate micronutrient contents in fertilizer mixtures. From the agronomic point of view, the total content is an inadequate criterion for the determination of micronutrient contents in chemical fertilizers.
micronutrients; mixed fertilizers; extracting solutions
