Influence of Soil Physical Properties on Agricultural Water Management Practices and Water Quality Impacts.

Soil physical properties often dictate the types of management practices that can be implemented for optimum crop production. In Tri-county Agricultural Area (TCAA) of northeast Florida, the soil profile comprises of a very sandy surface layer underlain by an impervious hardpan, approximately one meter below the soil surface. Taking advantage of this natural occurrence, potato and other crop fields in the TCAA are typically irrigated with subsurface seepage irrigation where a perched water table is created above the impervious layer by pumping water onto the surface, and the water table depth is controlled with the help of riser boards in strategically located ditches around the fields. Capillary water reaches the rootzone rising through the sandy surface layer. Due to the nature of the soil profile, the irrigation method and the drainage system, TCAA is regarded a potential source of nutrient contamination in the Lower St. Johns River. Study of the variation in the soil properties of the soil in this area is therefore very important for a better understanding of the mechanism of nutrient loss from the area. The main objectives of this study were to determine the spatial variation, both of surface and surface soil layers, in soil texture, bulk density, saturated hydraulic conductivity and moisture retention characteristics, in a typical seepage irrigated potato field of TCAA. Seventy soil samples were collected at five depths: 22.5cm, 45cm, 67.5cm, 90cm and 120cm, at the center of square grids of 26×26m size from a 4.2 hectare field. Variation in texture, bulk density and hydraulic conductivity will be studied using semi-variogram analysis of the data. A 3-dimensional variation map of the field based on spatial variation models will be developed, providing better understanding of the current management practices and potential water quality impacts.