The Efficacy of Lime, Gypsum and Their Combination to Ameliorate Sodicity in Irrigated Cropping Soils in the Lachlan Valley of New South Wales

Two primary factors controlling dissolution rate of lime and gypsum chemical ameliorants are magnitude and frequency of water infiltration. Thus, it could be expected that longevity of these amendments is reduced under irrigated-systems, relative to dryland-systems. This paper examines efficacy of single and combined applications of lime and gypsum in two irrigated agricultural soils used for cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) production. Full-field, replicated experimental-strips consisting of control (L0G0) and combinations of 2.5t/ha lime (L2.5) and/or gypsum (G2.5), and of 5t/ha lime (L5) and/or gypsum (G5) were applied; there were seven treatments, that is, L0G0, L2.5G0, L0G2.5, L2.5G2.5, L2.5G5, L5G2.5, and L5G5. For both soils, exchangeable and soluble cation concentrations, cation exchange capacity (CEC), pH, electrical conductivity (EC), residual gypsum, aggregate stability in water (ASWAT), and crop production were measured 6 months and 2.5 years after amendment application. Exchange efficiency of calcium (Ca2+) applied as amendment was calculated after 6 months. Exchange of Ca2+ for sodium (Na+) was primarily attributable to gypsum, and generally at the higher rate at 6 months; effects did not persisting over 2.5 years. The EC effect of gypsum was not observed after 6 months or 2.5 years post-gypsum application and 12.85ML/ha of infiltrating irrigation-water/rain. Results indicate using lime and gypsum singly, or in combination, at low agronomic rates is not necessarily viable for broadacre-irrigated-agriculture on alkaline clayey soils.