In an attempt to enhance the precision of chemical analyses of soil fertility and quantify different elements simultaneously, some laboratories have opted to use the technique of inductively coupled plasma for optical emission spectrometry (ICP) instead of the technique of Atomic Absorption Spectrometry (AAS), which currently is the most commonly used in soil analysis laboratories. In this study we compared the precision of the two dosage techniques, their repeatability and the magnitude of the concentrations of the micronutrients Fe, Zn, Cu and Mn, extracted through Mehlich-1, Mehlich-3 and DTPA-TEA; Additionaly, we aimed to select the wavelengths of lowest spectral interferences with the ICP. Thirty-six soil samples (0 to 0.2 m) from the states of Minas Gerais and Bahia, Brazil, with varied micronutrient concentrations were used. To define the ICP wavelengths and to evaluate the precision and repeatability of the dosage methods, three of the 36 collected soils were selected. The wavelengths with the lowest spectral interferences in the ICP were: 259.939 nm for Fe in Mehlich-1 and DTPA-TEA and 234.349 nm in Mehlich-3; 213.857 nm for Zn and 324.752 nm for Cu in the three extractors; and 259.372 nm for Mn in Mehlich-1 and DTPA-TEA and 260.568 nm in Mehlich-3. Both ICP and AAS were precise and reproducible for Fe and Mn dosage, while ICP, owing to the lower detection limit, was more precise and reproducible in the Zn and Cu dosages. The dosage methods differed statistically (p < 0.01) by the identity test applied for the Zn, Cu, and Mn dosages, using Mehlich-1, Mehlich-3 and DTPA-TEA, which affected the interpretation of the ICP results, based on the critical levels of AAS.
chemical soil analysis; ICP; comparison of methods; precision; reproducibility
