The Effect of Water Table Management on Productivity and Water Quality
R. A. Cooke,* J. K. Mitchell
University of Illinois; U.S. Department of Agriculture

The primary objective of this project is to optimize the performance of subsurface drainage systems. Procedures are being developed to map existing drainage systems and to estimate the effective regions of influence of random drainage systems or monotiles.

The goal of this project is to characterize the effects of preferential flow paths in sludge-amended soils. Field work involves the monitoring of drain flow to obtain data to test the equivalence of infiltration rate, permeability, and effluent water quality from sludge-amended and non-amended plots. Laboratory analysis involves the evaluation of temporal variations in permeability from soil cores subjected to water in which the variation in water quality covers the range of the ionic strength of divalent cations measured in leachate from municipal sludge.

Dissolved phosphorus was measured in runoff from simulated rainfall applied to two soils and several tillage treatments used in an annual crop rotation of corn and soybeans. The average concentration and load of soluble P in the runoff were significantly greater from the no-till than from other tillage treatments. Only moldboard plowing after surface broadcasting of P fertilizer reduced the soluble P concentration below 0.05 mg-P/L. For the Catlin soil, a variety of tillage practices (disk, field cultivation, and strip-till) appeared to result in soluble P concentrations of approximately 0.14 mg-P/L. For the Tama soil, disk-harrow followed by field cultivation and harrow after fertilizer application appeared to reduce soluble concentration in the runoff to approximately 0.06 mg-P/L.

During the first five years of the Little Vermilion River Nonpoint Source Hydrologic Unit Area Project, researchers have monitored nitrate concentration and flow in the tile drainage systems on eight sites. Optimal nitrogen management practices for the seven cropped fields will be determined and applied. The specific practices that are optimal and practical for a particular farm will vary depending upon soils and the farmer's time constraints at different times of the year. We anticipate that the nitrogen management plans, once adopted, will produce more profit for the farmers and, thus, the farmers will continue to use the recommended practices long after the financial remuneration is available.