|The Iowa Management System Evaluation Area has three research sites Treynor, near Council Bluffs; Walnut Creek, near Ames; and Nashua, 40 miles north of Waterloo that characterize 35 percent of the corn and corn/soybean rotation acreage in Iowa.
At Treynor, four long-term watersheds characterize the conditions in western Iowa. The deep loess soil overlies rolling glacial till. Topography is characterized by narrow, gently sloping ridges, steep side slopes, and well-defined alluvial valleys. Detailed studies at Treynor emphasize the movement and persistence of atrazine, metolachlor, and nitrate in soil, in surface runoff, and in seepage flow.
At Walnut Creek, the topography is nearly level with no defined surface runoff features. The region is dotted with prairie potholes that are connected to the stream with tile drain lines. Movement of water to the ground water is slow through the glacial till. The watershed is being studied from a holistic approach to blend farming practices, land use, hydrology, and ecology.
At Nashua, level to gently rolling slopes and glacial till soils with high water holding capacity and moderate to poor drainage characterize the agricultural setting in northeastern Iowa. One acre experimental plots and tile drains overlie an aquifer in carbonate rock. The quality of tile drainage waters and movement below the tile is being studied.
In all three areas the underlying waters contained nitrates and pesticides prior to initiation of the MSEA. A 1988 assessment of western Iowa showed nitrate nitrogen in shallow wells at 1.8 parts per million (ppm); 24 percent of the wells had atrazine up to 24 parts per billion (ppb) with a median of 0.3 ppb. Deeper wells below 150 feet showed less consistent detections of nitrate and herbicides. Nitrate nitrogen in excess of 70 ppm and atrazine of 7 ppb were also detected in tile drainage and field runoff.
STUDY OBJECTIVES AND RESULTS:
Measure the impact of prevailing and modified farming systems on the content of nutrients and pesticides in ground and surface water.
- At Walnut Creek, atrazine exceeded 25 ppb and metolachlor exceeded 80 ppb in surface water during spring runoff.
- A Metolachlor concentrations were detected in snowmelt runoff at less than 20 ppb.
- A Volatilization of metolachlor occurred within 10 days after application and the amount lost was dependent upon soil surface and atmospheric conditions.
- A Concentrations in runoff are a function of time after application.
- A At Nashua, rapid chemical movement to tile drains was attributed to preferential flow.
- A Alachlor and metribuzin have not been detected in shallow wells installed beneath tile drains. Atrazine and metolachlor were rarely greater than 1 ppb and nitrate-nitrogen was 5 to 10 ppm in shallow wells less than 10 feet deep.
- A Nitrate-nitrogen concentrations in tile drains ranged from 15 to 20 ppm regardless of the crop.
- A Detections of herbicides in rainfall were most prevalent during the April to July period.
- A Surface water moving into tile inlets caused an increase in herbicide concentrations in tile drains.
- A Ridge tillage and no-till systems improved infiltration and reduced runoff at all sites; at Treynor and Nashua these practices led to increased leaching.
Identify and increase understanding of factors and processes that control fate and transport of agricultural chemicals.
- Atrazine adsorption is related to organic matter and water holding capacity and varies within fields.
- Lateral flow through glacial till soils transports pesticides across a landscape.
- Herbicide and nitrate movement across a landscape are linked to variations in soils, and in chemical and biological processes.
- Denitrification within the glacial till reduces the nitrate levels in the shallow ground water ( less than 60 feet deep).
- Water use patterns by crops in the early part of the growing season are influenced by the tillage and residue management practices and affect potential nitrate and herbicide leaching.
- Nitrate-nitrogen losses from Walnut Creek represent $10 to 20 per acre each year.
Assess the impact of agricultural chemicals and practices on ecosystems associated with agriculture.
- Nitrate cycling processes in the stream and streambed at Walnut Creek limit nitrate movement into water beneath the streambed.
- Buffer and filter strips benefit the quality of surface runoff into streams, primarily through adsorption of herbicides in the upper 2 inches of soil.
- Wetlands can effectively remove nitrate-nitrogen and herbicide from runoff; and 1 acre of wetlands per 100 acres of cropland could reduce nitrate concentrations to less than 10 ppm.
Assess the benefits to water quality of modified farming systems in the Midwest.
- Residue management increases infiltration, reduces surface runoff, and improves surface water quality.
- Postemergence application of herbicides reduced their presence in the environment and changed their pattern of movement in the landscape.
- Split nitrogen applications and delayed tillage or no-till reduced nitrate in tile drainage and shallow wells.
- Nitrogen management is being changed in a 1200 acre subbasin of Walnut Creek from fall anhydrous ammonia to spring starter and sidedress nitrogen based on soil tests.
Evaluate the social and economic impacts of using alternative management systems.
- Farmers are seeking more information on weed management and nitrogen management for all tillage practices and crop rotations.
- Farmer interest is growing in methods to improve nitrogen use efficiency, decrease the herbicide costs, and decrease the weed pressure.
- Weed pressures are continuing to increase in corn-soybean rotations and may require alternative crop rotations to break weed cycles.
Transfer appropriate technology for use.
- Scouting for pest populations can potentially reduce pesticide use.
- Soil testing and late spring nitrate tests are being used to reduce nitrogen fertilizer application without reducing yield.
- Understanding variations in weed populations within fields provides insights into weed management efficiency.
- Awareness of nitrate loss from fields has developed greater farmer understanding of practices required to improve nitrogen use efficiency.
- Best Management Practices that reduce surface runoff reduce the potential movement of atrazine and metolachlor into surface water.
- Nitrogen management practices in the loess soils will require soil tests and fertilizer applications more closely linked to crop needs.
- Water quality can be positively impacted through adoption of field and offsite management practices.
ARS: Jerry Hatfield 515-294-5723
CSRS/ISU: James Baker 515-294-4025
CES: Jerry Miller 515-294-1923
NRCS: Roger Link 515-284-4260
EPA: Robert Swank 706-546-3128
USGS: Robert Buchmiller 319-337-4191