COMPARISON OF CONVENTIONAL AND ALTERNATIVE DETERMINATION METHODS FOR COPPER, IRON, MANGANESE AND ZINC IN MEHLICH-1 EXTRACTED SOIL SOLUTION

In Brazilian laboratories, the determination of micronutrient contents for soil fertility analyses is based on extraction with Mehlich-1 solution (M-1), at a 1: 5 w/v soil: extractant ratio, with subsequent quantification by atomic absorption spectrometry (AAS). However, many laboratories also use a 1: 10 w/v soil: extractant M-1 ratio for the determination of macronutrients, and/or quantification by optical emission spectrometry with inductively coupled plasma (ICP OES), instead of AAS. As comparative studies between the micronutrient concentrations obtained by these alternative methods are scarce, the aim of this work was to investigate significant differences in results from these different extraction and quantification methods. In this work, statistical analysis showed that the Fe and Mn concentrations using both soil: extractant M-1 ratios (1: 5 and 1: 10) and Zn concentrations at 1: 10 w/v soil: extractant M-1 ratio were similar regardless the quantification equipment. Howeve, the Cu concentrations using both soil: extractant M-1 ratios and the Zn concentrations at 1: 5 w/v soil: extractant M-1 ratio differend according to the equipment used to quantifiy these nutrients. Also, all Cu, Fe, Mn and Zn concentrations determined at 1: 5 w/v differed from those at 1: 10 w/v soil: extractant M-1 ratio, regardless of the quantification technique. Most of these concentrations were higher at a ratio of 1: 5 w/v and affected the classification of the contents. It is therefore not recommended to use a soil: extractant ratio of 1: 5 for the extraction of the micronutrients Cu, Fe, Mn and Zn from soil samples.