Auxins in Some American Soils

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Abstract
A proximate method is described for the extraction and assay of auxin in soils. 100 gm. of soil is shaken at intervals for 48 hrs. with sufficient lime water to keep the pH between 7 and 8 in a volume of 400 ml. The filtered extract is then concentrated and auxin measured by the standard Avena test. Auxin detns. were made on the 2 upper horizons of 11 virgin soils representative of 4 of the great soil groups in the U. S. In very fertile midwestern surface soils and subsoils auxin was found to the extent of about 0.175 [gamma] per kg. of soil (indoleacetic acid equivalents); in less fertile soils considerably less auxin was found in the surface horizons and little if any in the 2d horizon.