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6697810 
Journal Article 
Critical Comparison of Humic Acid Test Methods 
Lamar, RT; Talbot, KH; , 
2009 
Yes 
Communications in Soil Science and Plant Analysis
ISSN: 0010-3624
EISSN: 1532-2416 
TAYLOR & FRANCIS INC 
PHILADELPHIA 
2309-2322 
WOS:000274285300001 
The colorimetric method and the California Department of Food and Agriculture (CDFA) method of evaluating the humic acid content of five raw humate ores and three humate products were compared to the classical technique of extraction in a dilute base followed by precipitation of humic acid by extract acidification and ash removal by hydrochloric/hydrofluoric acid (HCl/HF) wash. Compared to the classical procedure, the colorimetric and CDFA methods overestimated the humic acid content of the eight samples by 120% and 52%, respectively. Therefore, these procedures do not produce a reliably accurate value for the humic acid contents of humates and products produced using materials extracted from them.