Hydraulic Properties of Three Mississippi River Alluvial Soils Under Row Crop Production.

Mississippi River alluvial soils range from fine to medium texture and in most cases a single row crop farm will have as many as four soil textural classes. This leads to variability of soil hydraulic properties which may consequently affect solute and water transport. We conducted a study to characterize and compare soil hydraulic properties of three soil series (Sharkey clay, Commerce silt loam, and Commerce clay loam) under non-irrigated corn (Zea mays) production in the Mississippi River Delta. Tension infiltrometer was used to measure unconfined, unsaturated infiltration over a range of descending water tensions (15, 10, 5, and 3 cm) at the surface and 15 cm depth. Undisturbed cores were extracted from the two depths to measure bulk density (r_b) and water retention curves θ(h) determined using the WP4 DewPoint PotentiaMeter.  The Wooding’s equation for steady state flow from a disk source was used to estimate unsaturated hydraulic conductivity K(h) over the range of tensions. The van Genuchten-Mualem model was used to fit K(h) and θ(h) data to parameter values for each soil and depth using the optimization computer code, RETC. Mean hydraulic conductivities in the Commerce soils were not significantly different (P≤0.5). Mean hydraulic conductivities were significantly higher in the Sharkey soil at 3 and 5 cm of water tension than the Commerce soils (P≤0.5), which suggests that during initial rainfall events higher infiltration rate will occur in the Sharkey due to macropore flow. When macropore flow was eliminated by exerting higher tensions (10 and 15 cm of water), there was no significant difference between soils and depths (P≤0.5). The fitted water retention curves showed significant difference between the Commerce soils and Sharkey clay.