Extratores de potássio em fontes alternativas

Abstract

To evaluate and develop new methods for determining potassium solubility in alternative fertilizer sources, a greenhouse experiment was conducted using pearl millet grown in two soil types: a Dystrophic Red Oxisol (Latossolo Vermelho distrófico) and a Typic Orthic Quartzipsamment (Neossolo Quartzarênico órtico típico). Twelve ground potassium-rich rock materials were applied at a rate equivalent to 600 mg K₂O dm⁻³ of soil. For comparison, a treatment with potassium chloride (KCl) as the standard fertilizer and an absolute control without potassium addition were included. All other nutrients were supplied in sufficient amounts to meet the crop requirements. The experiment was arranged in a completely randomized design with 13 treatments. Data were subjected to analysis of variance (ANOVA), and treatment means were compared using the Scott-Knott test at the 5% significance level. The fertilizer sources were analyzed using the following extraction methods: water (official method); 2% citric acid solution; neutral ammonium citrate (NAC); 2% citric acid + 0.5% ammonium fluoride solution; 5% tartaric acid solution; and 5% tartaric acid + 0.5% sodium fluoride solution (newly proposed methods). At the end of the pot experiment, the following variables were evaluated: soil-extractable potassium after cultivation, soil silicon content, pearl millet shoot dry matter, and the concentration and accumulation of calcium, magnesium, and potassium in plant tissue. Potassium uptake by the plants was correlated with the potassium recovery obtained by each analytical method. Among the evaluated extraction methods, the 2% citric acid + 0.5% ammonium fluoride solution showed the strongest correlation with plant potassium uptake and was therefore identified as the most suitable method for assessing insoluble potassium sources, followed by the neutral ammonium citrate (NAC) method