| Abstract
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Eleven saline-sodic soils in the Indus Plain of Pakistan were studied to characterize their profiles with respect to permeability to water, texture, pH, and soluble ions of Na, Ca, Mg, Co3\sp{2-}, HCO3\sp-, Cl, and SO4\sp{2-}. Surface and subsurface permeabilities were low, with values mostly between 1 usd\timesusd 10 m s and 5 usd\timesusd 10 m s. The analyses of the well waters collected from the sites indicated high adjusted sodium adsorption ratios (SARs). The formation of saline-sodic soils in the Indus Plain seems is related to the long-time use of poor-quality irrigation waters. NH4HCO3 + DTPA-extractable K, P, Fe, and Mn were deficient in some soils, while Zn was deficient in all the studied soils. A field experiment on a low permeability, saline-sodic soil compared the effect of various reclamation treatments. Treatments were: (1) deep-rooted perennial alfalfa, (2) sesbania-wheat-sesbania rotation, (3) incorporated wheat straw at 7.5 Mg ha and, (4) fallow. These four treatments were each combined with and without gypsum, with and without drainage, and with and without subsoiling. Field-saturated hydraulic conductivity (Kfs), SAR, soluble salts, Cl, and pH were measured to 120 cm depth, in 20 cm increments. Infiltration rate (IR), and penetrometer cone index (CI) were measured to evaluate improvement in the surface soil permeability. NH4HCO3 + DTPA-extractable K, P, Fe, Mn, Zn, and Cu were measured for changes in the nutritional status during reclamation. Gypsum application in the cropped plots improved the soil physio-chemical properties by increasing Kfs and IR, and decreasing SAR, Cl, and pH. In fallow plots, gypsum increased soluble Na in the soil profile, which slow percolating water did not leach. Eventually, the soluble Na remaining will again exchange for exchangeable Ca, which will precipitate during dry periods as carbonates and silicates. Alfalfa, with gypsum, increased Kfs and decreased SAR to a 80-cm depth. Improvement in the surface soil was greatest under crop rotation. The crop rotation also increased extractable K, P, Fe, Mn, Zn, and Cu in the top 20 cm of soil. In summary, a combination of gypsum plus sesbania-wheat-sesbania rotation produced the most surface soil improvement. Gypsum plus alfalfa was the most effective on deeper soil layers.
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