Abstract
A turbidometric technique has been developed to quantify the coarse and fine clay in soil. This helps to elucidate the variations of clay sizes and amounts in the soil samples. The technique will be useful for pedologists in order to evaluate the coarse to fine clay ratio (C/F) of various soil series, which sometimes clearly demonstrate the illuviation (clay movement, translocation and deposition) process to be operative in the soil profile, which otherwise could only be concluded after studying the soil thin-sections with very specialized equipment. These equipment arc not easily available in laboratories. The turbidometric technique also gives close agreement for the total clay values (<2 Am) to those as measured by the routine hydrometer method.
INTRODUCTION
Soil texture is important in the sense that it is a major factor in water holding capacity, permeability, infiltration rate, consistence and porosity etc.. The analysis for soil texture can be made in the field and more accurately, in the laboratory. However, the quantification of the liner day fractions poses problems in the routine analysis of soil texture. Possible alternative technique to quantify the various size ranges within clay fraction, the use of Coulter Counter (Coulter Electronics, Inc., 1975) has also been investigated. Samples were prepared according to Pennington and Lewis, (1979), but this technique was found to be inadequate to quantify particles below 0.4 Am. The lower limit for the Pipette method is (cumulatively) less than 0.2 Arn, further quantification of finer clay is impossible by the existing routine techniques. It was therefore a need to develop a technique
which measures all size ranges within the clay fraction. 'It was for this reason that a turbidometric technique was developed, which allows the quantity of the various sizes of clay to be measured through the measurement of the optical density of the clay suspensions in spectrophotometric glass tubes. This measurement of coarse/fine clay is helpful to elucidate the results of clay migration in the soil profile, a pedogenic process of world importance.
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MATERIALS AND METHODS
Two disturbed soil samples were collected at 65-70 cm depths of the Lyallpur camborthid) and Khurrianwala (natric camborthid) soil series. These were air dried and sieved (less than 2 mm) for routine analysis. Routine physical and chemical measurements were carried out according to the methods as prescribed by Richards (1954) except otherwise mentioned.
