ANÁLISE DE CALCÁRIO AGRÍCOLA: ESTUDO COMPARATIVO DE VIABILIDADE QUÍMICA-ECONÔMICA EM ENSAIOS DE CONTROLE DE QUALIDADE

Abstract

In Brazil, much of the soil destined for the agribusiness sector has high acidity, since the rocky environment of origin, the continuous use of fertilizers, the decomposition of organic matter and the possible removal of pre-planting natural substrates are factors that contribute to this outstanding characteristic. In plants, the high acidity of the soil can cause poor root development and this harmful effect can limit the use of water and nutrients. In this context, correcting soil acidity using agricultural correctives to increase crop productivity is an extremely necessary practice. However, for an agricultural corrective to be used safely and efficiently in agriculture, quality parameters such as RTNP (Relative Total Neutralizing Power), NP (Neutralizing Power), RE (Reactivity), in addition to levels of calcium (Ca) and magnesium (Mg) need to be evaluated. In this sense, this work presents a study on the practical aspects of methodologies involving the analysis of agricultural limestone, with a view to evaluating the precision and accuracy of the results of the quality parameters, similarity between the methods/procedures, in addition to aspects such as consumption and cost reagents and analytical frequency. The selected methodologies were those based on the method of the State Agency for Animal and Plant Sanitary Defense of MS (IAGRO) and the Ministry of Agriculture, Livestock and Supply (MAPA) with the determination of magnesium experimentally [Mg] and by theoretical method [Mg(t)] for both methods, in addition to defining the costs of reagents and analysis time. The results obtained for the evaluation of economic viability (cost for determination by sample) and the analytical frequency of the four methodologies were R$ 0.70 and 53 min, R$ 0.60 and 45 min, R$ 0.39 and 53 min, and R$ 0.28 and 44 min for Mg and Mg(t) IAGRO method and Mg and Mg(t) MAPA method, respectively. The similarity between the methods was evaluated by applying the paired t-test, which showed systematic differences between them. When the magnesium content was determined experimentally and theoretically, a tendency is observed that the experimental values are slightly higher, with an average difference of 1.5% and 2.3% for the IAGRO and MAPA methods respectively, when compared with the theoretical value. The precision and accuracy of the procedures were evaluated by participating in a national proficiency trial, where a single sample analysis was performed on 3 different days. Precision was obtained by calculating the relative standard deviation (RSD) between measurements, and values below 2.0% were achieved in the procedures. To assess accuracy, the value designated as true provided by the evaluating institute was used, and given this information, the relative error was calculated and less than 5.8%. Furthermore, an extremely important factor that deserves to be highlighted is that the parameters evaluated demonstrate that the values obtained are within acceptable limits to qualify the procedures/laboratories as proficient. Thus, it was demonstrated that the determination of theoretical Mg can be a viable alternative, as it increases the analytical frequency and reduces costs.