Spatial and Temporal Movement of Soil Nutrients in Southern Louisiana.

Nutrient runoff is a major contributor to non-point source pollution of Louisiana bayous. Yet the dynamics of runoff are often site specific and based on physicochemical soil factors, topography, proximity to surface waters, etc. Movement of nutrients across landscapes was studied at three sites in St. Landry Parish, Louisiana. Pasture site one (PS1) and Pristine site (PR) were directly adjacent to Bayou Wikoff. Pasture site 2 (PS2) is ~130 m from Bayou Wikoff.  All soils at the three sites are mapped as silt loam (Jeanerette, Frost, and Patoutville series).  Both PS1 and PS2 support improved, fertilized pasture used for haying and livestock. Both fields have been historically modified with broad, low rise furrows. Conversely, PR is an organic tree farm with no history of inorganic fertilizer application. A total of 368 georeferenced surface samples (0-5 cm) were collected across the three sites. Three samplings were conducted: September 2008, January 2009, and May 2009. Standard soil physicochemical analysis was performed in the lab, with nutrient concentrations evaluated via Mehlich III extraction and ICP quantification. Nutrient data was interpolated using ArcGIS Kriging and IDW techniques. Spatial variability of nutrient concentrations was examined. In response to heavy rainfall, temporal shifts in nutrient movement were also studied. Data from the study will be used to: 1) predict nutrient runoff potential from other farms with similar site conditions and management, and 2) govern precision agriculture applications of future fertilizer to minimize cost to the farmer and nutrient loading to the fields.