Aerial Infrared Mapping of Subsurface Drainage Systems
R. A. Cooke,* M. C. Hirschi, J. D. Davis
Illinois C-FAR

The primary objective of this project is to provide researchers, farmers, farm managers, policy makers, farm organizations, and agribusiness interests in Illinois with maps that show the layout of subsurface drainage (tile) systems in the Lake Decatur watershed, one of the most heavily tiled watersheds in the state. Drain (tile) mapping is possible because the soil over efficiently draining tile lines dries faster than the soil at other locations in the field and has higher reflectance in the infrared region of the radiation spectrum.

Incorporation of the Effect of Artificial Subsurface Drainage into Surface Water Quality Models
R. A. Cooke*
University of Illinois

Most of the agricultural lands in central Illinois are drained by artificial subsurface drains. These drainage systems provide alternate pathways for solute movement to rivers and streams. The goal of this project is to incorporate the effects of these systems into watershed-scale flow and transport models.

Management Practice Effects on Nitrate-N Concentrations in the LVR
J. K. Mitchell,* M. C. Hirschi, G. F. McIsaac
Illinois Council on Food and Agricultural Research; University of Illinois

Nitrates in subsurface tile flow have been monitored for six years from fields with various tillage and cropping management practices. The effect of the application of large amounts of nitrogen fertilizer, particularly as a preplant operation, was shown in the nitrate-N concentrations from the drains. The preplant anhydrous-N application systems with average nitrogen application of 107 kg/ha/yr had a had a mean concentration of nitrate-N of 16.8 mg/L in the tile drain outflow. Side-dress and manure application systems with average nitrogen application of 93 kg/ha/yr had a mean concentration of nitrate-N of 10.2 mg/L. The mean concentration of nitrate-N from a permanent meadow field was 1.0 mg/L.

Modeling Agricultural Practices for Water Quality Improvement Using GIS
J. K. Mitchell,* M. C. Hirschi, G. F. McIsaac, S. E. Walker
University of Illinois; U.S. Department of Agriculture

A study was conducted to examine the utility of the SCS curve number method for a 48,000 ha watershed in East-Central Illinois. The SCS-CN method did not perform well in predicting flow based on recommended curve numbers for this watershed. The SCS curve number method was modified for the tile flow situation; however, the terminology of many of the terms was changed. The modified curve number was used for successfully evaluating tile flow from tile drain systems. The predicted flow was not sensitive to the fraction of initial abstraction to potential maximum retention of the watershed.