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Abstract
The purpose of the study was to determine the chemical, physical, and morphological changes which had occurred in a saline-sodic soil (Typic Natrargid) after it had been reclaimed. Study sites were selected which had been reclaimed for a minimum of 5, 8, 15, or 25 years. The properties of soils at these sites were compared to the same soil in its natural state.
Irrigation and leaching removed approximately 7 x 10('4) kg of soluble salt from the upper 100 cm of the soils in approximately five years. There was little additional removal of salt with time and the soil solution attained an apparent steady-state with the solid phase after approximately 15 years. Reclamation reduced the electrical conductivity of the soil saturation extracts to levels which would be detrimental to only the most salinity-sensitive crops. The sodium adsorption ratios in extracts from the reclaimed soils were a function of the soils' mineralogy and were not found to be related to the SARs of the irrigation waters.
Scanning electron microscopy revealed that surface textures of quartz grains in the soils were being altered primarily by the precipitation of silica (Si) on the grain surfaces. Evidence existed which suggested that in the reclaimed soils, Si had precipitated in a more crystalline form than in the undisturbed soil. Surface features attributable to chemical weathering were obscured by precipitated Si, indicating that the soils were once subjected to a more intense weathering environment.
Scanning electron microscopy also revealed that in the reclaimed soils, smectite minerals had undergone hydrolysis. X-ray diffraction analysis supported this, and showed that smectite had been altered to kaolinite in the reclaimed soils. Smectite hydrolysis was also reflected in a reduction in water dispersible clay in the soils after 15 years of cultivation.
Methods were developed to help determine whether pedogenic CaCO3(s) precipitated from the soil solution by evaporation or CO(,2)(aq) losses, and to calculate the amount of pedogenic CaCO(,3) which had dissolved and reprecipitated during reclamation. Both techniques relied upon the stable isotopic composition of the soil CaCO(,3)(s). . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI
