Water flow in unsaturated soil below turfgrass: Observations and LEACHM (within EXPRES) predictions

In cropped soils, water sustains the plants, affects the transport of nutri ents within the root zone, and controls the leaching of nutrients and chemi cals to ground water. The objectives of this study were (i) to investigate the effects of turfgrass on water flow in sandy loam soil during the growin g season using field Lysimeters, and (ii) to test the abilities of the mode ls EXPRES and LEACHN with free-drainage and lysimeter bottom-boundary condi tions, respectively, to simulate water movement in the lysimeters. Twelve f ield lysimeters were parked with a three-horizon profile, topped with Kentu cky bluegrass (Poa pratensis L.) sod, and monitored for 2 Sr. Saturated hyd raulic conductivity, measured on cores, was much greater and more variable for turf than soil. The moisture-retention curve for turf also had a much s teeper drop in water content at low applied negative head than soil. The ly simeters became very dry during the summer, and only drained during the spr ing and autumn. The model EXPRES generally predicted water now well, but ha d some difficulty with water redistribution during the drying periods (grav ity drainage and evapotranspiration). In general, with the free-drainage bo ttom-boundary condition, EXPRES predicted more drainage and less drying dur ing the summer than was observed. Under conditions of Little to no irrigati on, the free-drainage condition over-predicted and the lysimeter condition under-predicted the total amount of measured drainage. Model predictions of drainage under heavily irrigated conditions were similar for both bottom-b oundary conditions.