ELECTROMAGNETIC CONDUCTIVITY SURVEYS OF DAIRIES FOR GROUNDWATER NITRATE

A recent study of dairies in a five-county area in north Georgia found a high incidence of NO3 contaminated well water, We used a ground electromagnetic conductivity meter to survey eight dairies in the region to determine the source of contamination. Ground conductivities were highest in the leafing areas on most dairies. These are the corrals or small fields near the barn where the milking herd is kept when it Is not in the barn or on pasture and other areas near the barn where there is high animal traffic, Conductivities were typically 15 to 20 mS m(-1) in these areas, compared with <10 mS m(-1) in the pastures away from barns, Water samples from groundwater monitoring wells installed in the leafing areas on three dairies to depths of 7 to 10 m had NO3-N concentrations between 47 and 135 mg L(-1). Shallow ground conductivities in the vicinity of these wells were 10 to 24 mS m(-1). There was evidence of seepage at three of the six lagoons we surveyed, but the leafing areas appeared to be a greater threat to drinking water supplies because they were closer to the milking barn where the supply well was located. Stocking rates were probably high enough in the leafing areas to result in excessive N deposition from manure, but not high enough to cause anerobic conditions that would inhibit mineralization or promote denitrification. Best management practices need to be developed that address NO3 leaching from loafing areas.