AGRICHEMICAL TRANSPORT TO GROUNDWATER THROUGH COASTAL PLAIN SOILS

Abstract

A 1ha field with Pine Flat loamy sand (coarseloamy, siliceous, thermic Typic Paleudult) and Troup loamy sand(loamy, siliceous, thermic Grossarenic Kandiudult) surface soils, located near Plains, Georgia, was studied for four years(1993 to 1996) to evaluate potential agrichemical transport to groundwater. The field was managed to produce summer cornand winter wheat. Commercial fertilizer, the herbicide atrazine, and the insecticide carbofuran were applied to the field in1993, 1994, and 1995. Average annual application rates were 266 kg nitrogen ha1, 2.5 kg atrazine ha1, and 2.4 kgcarbofuran ha1. Monthly soilwater and groundwater samples were collected. The samples were analyzed for nitratenitrogen (NO3N), chloride, atrazine, carbofuran, and deethylatrazine (DEA). Soilwater and groundwater samplesindicated elevated NO3N concentrations (>5 ppm) in the vadose zone at 4.3 m and in the aquifer at 10 m (>4 ppm). Of thestudied pesticides, carbofuran and DEA were observed at the greatest concentrations in groundwater.<br><br>Both NO3N and pesticides were transported during groundwater recharge following periods of excess precipitation.Peak pesticide concentrations in groundwater were observed in late 1994, driven by a large precipitation event in July of 1994when 565 mm of rain fell over a 4day period. Atrazine and carbofuran concentrations in groundwater did not exceed theEPA maximum contaminant levels of 3 ppb and 40 ppb, respectively. Spatially averaged concentrations observed in monthlygroundwater collected directly below the field were well below these standards. Concentrations of NO3N, atrazine, DEA,and carbofuran observed in groundwater from the onfield wells were significantly different from upgradient anddowngradient concentrations (p = 0.05). These data indicate a significant impact to the local groundwater. Nitrate N wastransported downgradient from the field at the largest concentrations. Peak concentrations of atrazine and DEA weresimultaneously observed in the groundwater, indicating similar transport rates for both compounds and rapid transformationfrom atrazine into DEA in the rootzone.