Laboratory Assays for Sodic Soil Reclamation.

High levels of soil exchangeable sodium (Na) cause structural changes that affect soil crusting, soil hydraulic conductivity, soil water availability, soil porosity and crop rooting extension restriction. A Paso Seco soil (Fine, mixed, superactive, isohyperthermic Entic Udic Haplusterts) classified as sodic (exchangeable Na greater than 15%) in Guayama municipality, Puerto Rico was used to evaluate the effects of three gypsum sources (Agricultural Gypsum, Phusion® Gypsum, Reagent-grade Gypsum). The soil was collected from various areas of the same field, pooled, dried and sieved. The soil with each gypsum source was amended with five levels (750, 1,500, 3,000, 6,000 and 12,000 mg/kg soil dry wt). Soils were packed in 60 mL microcosms and leachate volume, pH, and electrical conductivity (EC) were measured during four lixiviation events using a mechanical extractor in the laboratory. The leachate volume collected increased with increasing gypsum levels. Leachate pH decreased with increasing amendment rate and incremental leaching event. Leachate EC increased with amendment rate and decreased with incremental leaching event. Improved leaching and leachate characteristics were observed at lower rates with Phusion® Gypsum. Leachate composition (Ca, Mg, Na) analysis of the soil amended with 4,500 mg/kg of Phusion® Gypsum revealed that 73% of the exchangeable Na was removed in three leaching events reducing exchangeable Na to 4.73 cmolc/kg. Further analysis of the solution composition for Ca, Mg, and Na will demonstrate the predominant cations in leachate and will show the extent of exchangeable Na that is being leached.