Modeling Water Table Fluctuations During Subsurface Irrigation and Drainage In Sandy Soils.

Efficient management of shallow water table is one of the most critical aspects of crop production in low lying areas such as Florida. Proper understanding of the water table rise to (irrigation) and decline (drainage) from the crop root-zone is important to optimize the water supply, for which modeling approach can be very useful. In this study, water table dynamics in subsurface irrigated potato fields of northeast Florida was studied by numerical simulation of the non-linear Boussinesq equation of groundwater flow. An expression for the transient drainable porosity dependent on the depth to the water table, unsaturated moisture storage and steady state flux at the soil surface was derived and used in the simulation. Hourly water table data from the field was collected during the potato season of spring 2010 and compared with the simulation results. It was found that the diurnal variation in the water table strongly corresponded to the hourly evapotranspiration (ET) rate suggesting that most of the crop-ET demand is directly fulfilled by the water table. Comparison of observed and simulated water table data show good agreement for the water table movement during irrigation and drainage phases suggesting that the model can be used as a potential tool for optimizing irrigation-schedules in the area.