Photometric determination of humic matter in soils, a proposed method

There is need for a rapid, environmentally acceptable method to quantity the organic fraction In soils that has the greatest influence on herbicide bioactivity. A photometric method for measuring the alkali extractable humic substances is proposed. The extractant, 0.2N NaOH‐0.0032M DTPA ‐ 2% alcohol, poses no undue hazard in the laboratory or in the sewage disposal system. Any laboratory capable of soil testing can perform the test and, in high volume operations, at the rate of 500 per technician ‐ day. Preliminary laboratory and field studies suggest that the fraction of organic matter extracted is related to herbicide inactivation and could serve as a standard for the herbicide industry.