A comparison of the unsaturated hydraulic conductivities of calcareous and noncalcareous soils

In situ unsaturated hydraulic conductivities of calcareous soils have not been intensively investigated. The objective of this investigation was to compare the hydraulic properties of adjoining calcareous and noncalcareous soils in the field. Soils used for this investigation were the calcareous Estacado series (fine-loamy, mixed thermic, Calciorthidic Paleustoll) and the noncalcareous Friona series (fine-loamy, mixed, thermic, Petrocalcic Paleustoll). In situ, unsaturated hydraulic conductivities were determined in the Ap1, Ap2, Bt1, and Bt2 horizons of each soil. Water was ponded daily and allowed to infiltrate under falling head conditions. Water additions were terminated when the tensiometers in the Bt2 horizons indicated no change of soil water potential from the previous day. Plots were covered with Styrofoam and plastic to prevent evaporation. During infiltration and drainage, water potential was monitored with two replicated tensiometers within each soil horizon. Two replicated gravimetric soil samples were taken concurrently from each soil horizon and converted to volumetric water content. Soil water release curves were constructed from in situ soil water potentials and volumetric water content. Hydraulic conductivities were calculated using in situ change of soil water contents and soil water potentials with time. The noncalcareous soil had higher hydraulic conductivities than the calcareous soil at the same water content. The calcareous Ap1 and Ap2 horizons had higher hydraulic conductivities than the noncalcareous soil at the same soil water potential. In situ soil water release curves indicated that calcareous soil retained more water than the noncalcareous soil at the same soil water potential in the paired horizons. Unsaturated hydraulic conductivities increased with depth for both soils.