Nitric Acid as a Cold Extractor of Total Nutrient Contents from Mineral Fertilizers

Chemical characterization of fertilizers, in terms of total nutrient content, is essential for quality control and definition of field-based rates. The Ministry of Agriculture, Livestock and Supply (MAPA) by IN/2007 recommends different methods for nutrient content extraction for fertilizers. These methods can have high analytical costs, be laborious, and generate large quantities of residues. Therefore, this work proposes a simple and more environmentally friendly extraction method by using nitric acid solution to extract total content of nutrients from fertilizers, which has the advantage of a cold extraction, less residue generation, and easier execution. The experiment was carried out using eight nutrient sources (tricalcium phosphate, monocalcium phosphate, potassium chloride, zinc oxide, copper oxide, manganese oxide, ulexite, and a mixture of soluble sources of these nutrients), four nitric acid concentrations (0.0, 1.0, 2.5, or 5.0 mol L-1), and six shaking times (10, 20, 30, 40, 50, or 60 min). A completely randomized design with three replicates was used. These data indicated 2.5 mol L-1 HNO3 as suitable concentration to extract total nutrient content from the sources. In addition, as there was no shaking time effect on elements extraction; in a second trial, we compared the performance of HNO3- at 2.5 mol L-1 under a shaking time of 60 min across MAPA methods. The results evidenced that soluble contents extracted by both methods were highly correlated, recovering equivalent amounts of B and K. For other nutrients, nitric acid method extracted a greater amount than MAPA method. Therefore, this paper represents a first approach to the use of a method based on nitric acid for the recovery of total nutrient contents (P, K, Ca Mg, S, B, Cu, Mn, and Zn) in mineral fertilizers of varying solubility. [GRAPHICS] .