PHYSICAL AND HYDRAULIC-PROPERTIES OF A CALCIC HORIZON

Movement of water through well developed calcic horizons, present in many North American Great Plains soils, is critical to groundwater recharge and crop water management; however, information about the hydraulic properties of these horizons is scarce. This study was conducted to measure physical and hydraulic properties of a calcic layer under an Acuff fine sandy loam (fine-loamy, mixed, thermic Aridic Paleustolls) in the southern Great Plains near Lubbock, TX. Site characterization included bulk density, particle size distribution, and water retention measurements. The saturated hydraulic conductivity (K(s)) was measured with the constant head method and estimated from infiltration rate data fitted to three models. Unsaturated hydraulic conductivity (K(theta(v))) was calculated using measured and estimated values of K(s) and the measured soil water retention curve (theta(v)(h)). Mean bulk density was 1.44 +/- 0.2 Mg m-3, and the textural classes of the calcic layer with and without carbonates were clay and sandy loam, respectively. The measured vertical K(s) of 0.87 x 10(-5) m s-1 and model estimated K(s) of 1.20 x 10(-5) m s-1 were consistent with the K(s) of a coarse textured soil. However, measured (theta(v)(h)) was consistent with a fine textured soil. These data suggest that a calcic horizon would not greatly impede water movement, but drain rapidly instead. For example, water reaching the caliche layer from excess irrigation will drain rapidly below the root zone. Ground water recharge from draining surface basins (playa lakes or unsealed water treatment lagoons) would not be hindered.