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ARS Home » Midwest Area » Morris, Minnesota » Soil Management Research » Research » Publications at this Location » Publication #71579


item Olness, Alan
item Daniel, John

Submitted to: Irrigation and Drainage International Symposium Proceedings
Publication Type: Book / Chapter
Publication Acceptance Date: 5/23/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The prairie pothole region consists of several million acres of the northern Great Plains. This area produces large amounts of wheat, corn and soybeans, most of which is treated with pesticides and fertilizers. These prairie potholes are collection sites for snowmelt and rainfall that runs off the land, and often percolates into the groundwater. Thus, potholes are epotential sites for groundwater pollution. We conducted field experiments to determine if this was true. Our data showed that soil in the basins of these potholes are generally anaerobic (lack oxygen). Soil microbes must therefore obtain oxygen from other sources, one of which is nitrogen fertilizer washed in from surrounding land. Soil microbes remove oxygen from the nitrate portion of the nitrogen fertilizer, and the remaining nitrogen is released as a harmless gas. Thus, nitrate movement into the groundwater is minimal. Pesticides such as atrazine, however, are more soluble in soils under anaerobic conditions, and may move from the pot hol into the groundwater. These findings can be used by farm managers and action agencies to improve recommendations and use of nitrogen and especially pesticides in the prairie pothole region. Improved recommendations will minimize the risk of pollution of groundwater through use of agriculturally applied chemicals.

Technical Abstract: The prairie pothole region (PPR) of the northern Great Plains, often intensely used for production of wheat (Triticum aestivum L.), maize, (Zea mays L.) and soybean (Glycine max L.), is characterized by numerous shallow, glacially-derived depressions. These depressions collect surface runoff of snowmelt and rainfall from nearby fields which infiltrates to shallow groundwater as focused recharge. While only 2 to 5 % of the total precipitation is recharge to groundwater, depressionally focused recharge allows point-source recharge of rainfall and snow melt as frost melts during spring thaw. Nitrate levels increase over winter (5- to 20-fold), but spring recharge dilutes these increased concentrations. Relative measures of aeration made with platinum electrodes during the thawed period show that potentials in well-drained portions of the soil profile remain above + 400 mV throughout most of the crop year. Similar potential measures made in the base of a previously drained pothole were negative an well below the critical aeration potential for denitrification for most of the year. Therefore, it is unlikely that nitrates contained in rainfall- induced surface runoff moves through prairie potholes to groundwater. However, some bound pesticides such as atrazine and alachlor are solubilized under anaerobiosis. Anaerobiosis effectively doubled the amounts of resin extractable atrazine and alachlor from a wide range of soils. Thus, contamination of prairie potholes with pesticides may contribute to groundwater pollution when both anaerobiosis and leaching occurs.