Abstract
Samples from various layers of the Khurrianwala soil series (Nor's cambor-11:1(1) were subjected to hydraulic conductivity measurements. Hydraulic conductivity was measured with a set of treatments 1) distilled water (DW), 2) gypsum saturated solution (GSS), and 3) GSS + deep ploughing. The results revealed the operation of dispersion, translocation and deposition of clay particles into the conducting pores as the dominant mechanism in the upper three layers (0-5, 5-10 and 25-30 cm), whereas swelling in three deeper layers (45-50, 65-7(l and 125-130 cm).
INTRODUCTION
The hydraulic conductivity (HC) of the soil is either reduced by dispersion of clay particles and their subsequent deposition in the conducting pores or through swelling. The importance of dispersion in affecting soil permeability was recognised by Fel-hendler et al. (1974) and Shainbcrg of al. (1981 a, b). Recently Yousaf of al. (1987) discussed the clay dispersion with respect to HC of the soils. McNeal cif at. (1968) re-ported a linear relationship between the HC reduction and macroscopic swelling of ex-tracted clays. The swelling of clay may be crystalline swelling (Norish, 1954; Norish and Quirk, 1954) or osmotic swelling (El-Swaify and Henderson, 1967; Van Olphan, 1977). The measurement of soil NC is of great importance in practical agriculture since related to the movement of soluble salts and nutrients. It also helps to forecast the drainage capacity of the soil for agricul-ture and engineering purposes and provides indirect informations of soil structure.
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The present project was started to ass-ess the hydraulic conductivities of the dense saline-sodic soil profile, Khurrianwala soil series (Natlic Canillorthid) under simulated rain conditions and improvement by gypsum and finally with gypsum and deep ploughing. Moreover, it was aimed to elucidate the im-portant mechanisms operating in the soil profile that can result in the reduction of soil permeability.
MATERIALS AND METHODS
Bulk samples were collected from 0-5, 5-1.0, 25-30, 45-50, 65-70 and 125-130 cm depths of the Khurrianwala soil series (KWSS). Physical and chemical measure-ments were made on the soil ( <2 mm) ac.-cording to the standard methods (Page of al., 1982), except otherwise mentioned. Soil texture was determined according to Day (1965) and the textural class was determined on the basis of particle site grades of the British Standards Institution and the Mas-sachusetts Institute of Technology-MIT (Hodgson, 1976).
