Submitted to: Proceedings of the National Agricultural Ecosystem Management Conference
Publication Type: Proceedings
Publication Acceptance Date: December 15, 1995
Publication Date: N/A
Technical Abstract: Nonpoint source pollution from agricultural areas has been perceived to be the primary means of loading chemicals into surface and ground water sources. There have been few studies conducted on the watershed scale to identify the movement of agricultural chemicals. The Management Systems Evaluation Areas (MSEA) Program was developed to address the effect of current farming practices on surface and ground water quality in the Midwest. Research is conducted at 10 sites in five projects located in Iowa, Minnesota, Missouri, Nebraska, and Ohio. Walnut Creek watershed in central Iowa is one of the 10 sites and represents an intensively farmed watershed in the Des Moines Lobe landform region. Observations within the stream show that relatively little atrazine, metolachlor, alachlor, and metribuzin leave the watershed during the year. Herbicide concentrations in the tile drainage discharge are often near the detection limit of 0.2 ug 1**-1. Only atrazine and metolachlor have been detected once in more than 1700 ground water samples in excess of 3 ug 1**-1. Nitrate-nitrogen moves in the tile drainage discharge, and stream concentrations range from 10 to 20 mg 1**-1. Loads moving from the watershed vary from year to year depending upon the total discharge. These have ranged from 19,800 to 337,000 kg for the 5600 ha watershed, and these totals represent from 8 to 150 percent of the fertilizer nitrogen applied to the watershed. Temporal patterns of nitrate-nitrogen movement depend upon the overall stream discharge, and there is no spatial pattern of nitrate-N movement across the watershed. Management practices that would affect nitrate-nitrogen concentrations in the stream would have to be implemented on the majority of the fields.