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Turbidimeter Technique for Measuring the Stability of Soil Aggregates in a Water-Glycerol Mixture¹

ABSTRACT

A technique is described for measuring the aggregate stability of soil with mechanical agitation in a waterglycerol mixture. The technique consists of uniformly mixing a weighted soil sample in a 1000-ml. test tube containing a known water-glycerol mixture. After uniformly mixing, the test tube containing the suspension is immediately placed in a turbidimeter and the change in light transmission with time at a specific depth is measured using a recording potentiometer. The tube is removed after a specific time and the contents again mixed uniformly by a standard technique and an additional curve obtained. This process may be repeated as many times as necessary to obtain the breakdown trends of the aggregates with mechanical agitation. The mean weightdiameter of the soil aggregates in each run may then be determined by plotting the logarithm of th potentiometer reading vs. the square of the aggregate diameter (as callculated using Stokes' law) and measuring the area under the curve. The change in mean weight-diameter is a measure of the breakdown of the aggregates due to mechanical agitation in the water-glycerol mixture. Results show that the method measures differencers in structure not measured by the usual wet-sieve method.

¹ Technical Paper No. 1217, Oregon Agr. Exp. Sta. Research done under Regional Project W-30.

² Research Assistant and Associate Soil Scientist, respectively. Senior author is now a Laboratory Technician II in the Irrigation Department at the University of California, Davis.

Received for publication July 24, 1959. Accepted for publication November 9, 1959.