Assessing the effectiveness of management strategies to reduce agricultural nutrient efflux is hampered by the lack of affordable, continuous in-situ monitoring systems. Generalized water quality monitoring is possible using electrical conductivity. However environmental conditions can influence the ionic ratios, resulting in misinterpretations of established electrical conductivity and ionic composition relationships. Here we characterize the specific electrical conductivity of agricultural drainage waters to define these environmental conditions and dissolved constituents that contribute to electrical conductivity. Results from a field investigation revealed that bicarbonate, calcium, nitrate, magnesium, chloride, sodium, and sulfate (in order of decreasing ppm concentration) are primary dissolved constituents that contribute to the electrical conductivity of agricultural drainage waters. Analysis of seasonal drainage samples showed that bicarbonate, calcium, and magnesium were present at greater concentrations during the post growing season, while nitrate and chloride were greatest in the growing season. Seasonal variability of sulfate and sodium was negligible. Continuous corn and corn in annual rotation with soybeans had greater magnesium and chloride concentrations than that of soybeans in annual rotation with corn. Conversely, calcium was greater among soybean cropping systems compared to that of corn cropping systems. Bicarbonate and nitrate were not significantly different among any of the cropping systems. These changes in the ionic composition resulted in significantly different ionic ratios among the growing and post growing season samples, but not among cropping systems.