THE INFLUENCE OF SOIL TEXTURE AND IRRIGATION CHEMISTRY ON PEDOGENIC CaCO3 PRECIPITATION AND CO2 EMISSIONS OF AGRICULTURAL SOILS IN THE SOUTHWESTERN US

Recent studies of soils in agricultural fields in Tornillo, Texas have observed rapid salt accumulation as a result of flood irrigation, a common agricultural practice in drylands in the Southwestern United States. While the sources of evaporate salts including pedogenic carbonates have been identified and long-term accumulation rates estimated, little is known about short-term accumulation rates of these salts during each irrigation event and how those rates are controlled by soil horizons of differing soil texture and irrigation chemistry. The purpose of this study is to investigate the buildup of salts in typical irrigation events through column experiments in a controlled greenhouse. For the column experiments, two 20 cm-diameter, 80-cm tall PVC capsules were packed with sand-clay-sand layers to simulate contrasting soil texture observed in the field site. The sediments were irrigated by adding water of different chemistry and are monitored for temperature, soil moisture, electrical conductivity, pCO₂ and pO₂. The goal is to investigate the effects of time and salinity of irrigation water on pedogenic carbonate precipitation and CO₂ emission. After the irrigation, water has permeated, and the soils become dry, the sediments will be examined to: a) quantify the accumulation rates of salts; b) observe co-changes in soil moisture content, electrical conductivity, temperature, dissolved O₂ and dissolved CO₂, and c) to conduct chemical and isotopic analyses of pedogenic carbonate in layers of differing soil textures and relate to irrigation water characteristics.