Comparison of different methods for the determination of total organic carbon and humic substances in Brazilian soils

Revista Ceres

Raphael Bragança Alves Fernandes¹  Ildeu Afonso De Carvalho Junior¹  Emerson Silva Ribeiro Junior¹  Eduardo De Sá Mendonça¹ 

关键词: Walkley-Black method;    dichromate-oxidation;    loss on ignition;    método Walkley-Black;    oxidação com dicromato;    perda por ignição.;   

DOI  :  10.1590/0034-737X201562050011

来源: SciELO

【 摘 要 】

ABSTRACTAiming to compare three different methods for the determination of organic carbon (OC) in the soil and fractions of humic substances, seventeen Brazilian soil samples of different classes and textures were evaluated. Amounts of OC in the soil samples and the humic fractions were measured by the dichromate-oxidation method, with and without external heating in a digestion block at 130 °C for 30 min; by the loss-on-ignition method at 450 °C during 5 h and at 600 °C during 6 h; and by the dry combustion method. Dry combustion was used as reference in order to measure the efficiency of the other methods. Soil OC measured by the dichromate-oxidation method with external heating had the highest efficiency and the best results comparing to the reference method. When external heating was not used, the mean recovery efficiency dropped to 71%. The amount of OC was overestimated by the loss-on-ignition methods. Regression equations obtained between total OC contents of the reference method and those of the other methods showed relatively good adjustment, but all intercepts were different from zero (p < 0.01), which suggests that more accuracy can be obtained using not one single correction factor, but considering also the intercept. The Walkley-Black method underestimated the OC contents of the humic fractions, which was associated with the partial oxidation of the humin fraction. Better results were obtained when external heating was used. For the organic matter fractions, the OC in the humic and fulvic acid fractions can be determined without external heating if the reference method is not available, but the humin fraction requires the external heating.

【 授权许可】

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