Poster Number 545
Wednesday, 8 October 2008
George R. Brown Convention Center, Exhibit Hall E
Approximately 15,000 hectares of crop land in the Tri-County Agricultural Area (TCAA) in the lower St. Johns River (LSJR) basin in northeast Florida is planted annually to potatoes produced under subsurface seepage irrigation system. Occurrence of natural hardpan in the soil profile at approximately one meter depth helps maintain an artificial perched water table through continuous surface application of pumped water through out the crop growth period enabling adequate water supply to the rootzone through capillary rise. Continuous pumping of water into the field for maintaining water table renders the system inherently inefficient. Since, the perched water can only move laterally below the surface, continuous pumping of water on the surface creates a steady subsurface lateral drainage pathway, potentially flushing the soluble nutrients from across the field into the ditches and eventually into LSJR. The primary objective of this experiment was to determine the extent of subsurface lateral flow of water in the potato fields of TCAA by a tracer study, thereby providing an understanding of the mechanism for potential nutrient loss. A high concentration of KBr was injected into the perched water table through injection wells and water samples were collected at different intervals for 6 weeks from 90 monitoring wells in a 4.2 hectares field. The study was done during spring and summer seasons of both 2006 and 2007 to evaluate the effects of seasonal rainfall variation on the distribution of tracer. Bromide concentrations in water samples were determined and the data was statistically analyzed for establishing drainage patterns. It was observed that the distribution of the tracer in the field was directionally influenced suggesting the multidirectional slope of the subsurface hardpan. The study concluded that subsurface lateral flow of water was a significant phenomenon in the TCAA.