The search for methods to determine the content of soil organic matter (SOM) that do not generate hazardous waste is important. SOM oxidation with dichromate is used in most Brazilian soil laboratories and it generates chromium-contaminated waste. The objective of this study was to evaluate the weight loss-on-ignition (LOI) method in comparison to the wet digestion procedure based on sulfuric acid-chromium solution as commonly used in soil analysis laboratories of Rio Grande do Sul (RS) and Santa Catarina (SC) states, Brazil. The results obtained by the LOI method were further compared with the Walkley-Black standard-method, which also uses dichromate. The SOM content was determined in 19 samples from different soil units in RS and in 49 samples from the Central Depression of the same state. The 19 samples included: Vertisol (1), Gleysols (2), Argisols (6), Luvisol (1), Neosol (1), Latosols (3), Plinthosol (1), Planosol (1), Alisol (1), Nitosol (1), and Mollisol (1). Central Depression samples were provided by the Federal University of Santa Maria Soil Analysis Laboratory. The mean SOM contents obtained by LOI were 22 and 94 % higher than the means obtained with the sulfuric acid-chromium solution, and 27 and 46 % higher than that obtained with the Walkley-Black method, in Central-Depression and other RS soil samples, respectively. The LOI method was significantly correlated with the dichromate methodologies. Results indicate LOI for SOM analysis as a replacement of the dichromate methods. Equations that estimate the SOM content based on LOI should be developed for all RS soil classes.
Chromium; soil test; organic carbon; environmental contamination
