Fertilizer Nitrogen Practices and Nitrate Levels in Surface Water within an Illinois Watershed

Proper nitrogen (N) management as it relates to crop yield has become a critical concern due to the environmental impacts of excessive N fertilizer application. This study monitored 36 sites within the Lake Bloomington, Illinois, watershed on a weekly basis to determine nitrate-N concentrations from various surface water sources. Average nitrate-N concentrations for the period 1993 to 2002 revealed the following: agricultural production drainage tiles, 17.0 mg/L; creek water (Money Creek tributary), 12.0 mg/L; organic agriculture drainage tiles, 11.4 mg/L; surface water runoff, 6.6 mg/L; wooded pasture drainage tiles, 1.6 mg/L; and rainwater, 1.2 mg/L. In addition, as creek water passed through a small municipality ("urban effect"), its concentration of nitrate-N dropped by an average of 0.6 mg/L. An initial watershed resident survey and an annual N fertilizer use survey were conducted to ascertain common N management practices of agricultural producers within the watershed. The mean expected corn grain yield was 9845 kg/ha and the median N fertilizer application rate was between 169 and 202 kg N/ha. On average, 54.5% of the N fertilizer in the watershed was applied in the fall, 32.5% was applied in the spring before planting, and 12.7% was applied after planting. Within the watershed, 64% nonfarming residents perceived agricultural crop production as having the greatest negative impact on water quality compared with only 15.6% of those actively engaged in farming. Knowledge from this study can be used to develop recommendations for sound N management practices within sensitive watershed regions.