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A fall-planted winter cover crop is an agricultural management practice with multi-ple benefits that may include reducing nitrate (NO3) losses from artificial drained agricultural fields. While the practice is commonly used in the southern and eastern United States, little is known about its efficacy in midwestern states where winters are longer and colder, and artificial subsurface drainage is widely used in corn-soybean systems {Zea mays L -Glycine max L.).We used a field-tested version of the Root Zone Water Quality Model (RZWQM) to simulate the adoption of cereal rye (Secale cereale L.) as a winter cover crop and estimate its impact on NO3 losses from drained fields at 41 sites across the Midwest from 1961 to 2005. The average annual nitrogen (N) loss reduction from adding winter rye ranged from 11.7 to 31.8 kg N ha--1 (10.4 to 28.4 lb N ac-1) among four simulated systems. One of the simulated treatments was winter rye overseeded (aerial seeded) into a no-till corn-soybean rotation at simulated main crop maturity (CC2). On average, this treatment reduced simulated N loss in drainage by 20.1 kg N ha-1 (17.9 lb N ac-1) over the sites compared to systems without winter rye (NCC2), from 47.3 to 27.2 kg N ha-1 (42.2 to 24.3 lb N ac-1). Adding spring tillage to this treatment and killing the rye earlier (CC3) reduced simulated N loss from 57.3 (NCC3) to 34.4 kg N ha-1 (30.7 lb N ac-1). Replacing the corn-soybean rotation with continuous corn and spring tillage reduced simulated N loss from 106 (NCC4) to 74.2 kg N ha-1 (CC4) (94.6 to 66.2 lb N ac-1). Adding a winter rye cover crop reduced N loss more in the continuous corn system despite earlier spring termination of the winter rye and slightly less N uptake by the rye possibly because of more denitrification. Regression analysis of the RZWQM vari-ables from these sites showed that temperature and precipitation during winter rye growth, N fertilizer application rates to corn, and simulated corn yield account for greater than 95% of the simulated site-to-site variability in NO3 loss reductions in tile flow due to winter rye. Our results suggest that on average winter rye can reduce N loss in drainage 42.5% across the Midwest. Greater N loss reductions were estimated from adding winter rye at sites with warmer temperatures and less precipitation because of more cover crop growth and more soil N available for cover crop uptake. [ABSTRACT FROM AUTHOR]

Drainage water management (DWM) is a potentially valuable management practice for reducing NO3, losses to surface waters in areas of artificial drainage. But the practice is essentially untested in Midwest United States conditions and its water quality and crop yield benefits uncertain. This paper reports results from applying DWM to a 22 ha (54 ac) production field in central Iowa as part of a five-state Conservation Innovative Grant effort to document the impact of DWM across the Midwest. Three of nine plots in an existing tile drainage research site were retrofitted with control structures so that the drainage level could be controlled. Water flow from the tile in each plot, NO3 concentration in the drainage, and crop yield were measured over a four year period from 2006 to 2009.The field was in a two year corn (Zea mays L.)--soybean (Glycine max [L.] Merr.) rotation with nitrogen (N) fertilizer applied before the corn crop only. During four years of monitoring tile flow, there was a significant (p = 0.05) 21% decrease in tile flow, 110 significant decrease in NO3 concentration, and a significant 29% reduction in NO3 load leaching from the DWM treatment compared to conventional drainage. No yield benefits from DWM were observed for the two year average for corn (2006 and 2008),but a significant yield increase of 8% was observed for the two year average for soybean (2007 and 2009). For the four years monitored in this study, it is unclear if the yield increase for soybean versus no increase for corn was due to weather patterns or because corn and soybean responded differently to the raised water table caused by DWM. [ABSTRACT FROM AUTHOR]

Nitrate (NO,) losses from agricultural lands in the Midwest flow into the Mississippi River Basin (MRB) and contribute significantly to hypoxia in the Gulf of Mexico. Previous work has shown that cover crops can reduce loadings, but adoption rates are low, and the potential impact if cover crops were widely adopted is currently unknown. This paper pro-vides an analysis of potential cover crop adoption and relative benefits to water quality across the five-state region of Ohio, Indiana, Illinois, Iowa, and Minnesota in the upper midwestern MRB. Two agricultural counties were selected in each of the five states, and the potential for fall-planted cover crop adoption was estimated based on cash crop rotation and tillage sys-tems. In these 10 counties, an estimated 34% to 81% of the agricultural land could have cover crops integrated into their corn (Zea mays L.) and soybean (Glycine max L.) cropping systems. These adoption rates would in some cases require shifts of current tillage practices from fall to spring, but could be even higher with increased adoption of no-till and mulch-till. Nitrate reduction simulated with the Root Zone Water Quality Model for the tile drained portion of the corn-soybean and continuous corn cropping systems in the five-state area, under the assumed management systems and uniform soil properties, showed that cover crops have the potential to reduce N03 loadings to the Mississippi River by approximately 20%. These predictions suggest that cover crop adoption would have a beneficial impact on water quality in the MBJB and would contribute greatly towards meeting the national goal of significant reduction in N03-nitrogen (N) load entering the Gulf. [ABSTRACT FROM AUTHOR]

The application of site-specific conservation practices requires knowledge of spatial patterns in fields. This study evaluated two methods of delineating soil erosion patterns in a central Iowa field. First, soil erosion rates of individual grid based samples were estimated using soil displacement of cesium-137 (137Cs). Second, tillage and water erosion were estimated using the topography-driven Water and Tillage Erosion Model (WATEM). The tillage erosion map showed soil loss in convex shoulder positions and soil accumulation in concave footslope and toeslope landscape positions. Alternately, water erosion was associated with slope severity and slope length on backslopes. When the tillage and water erosion map patterns were combined a good correlation with the 137Cs soil erosion pattern was graphically and statistically exhibited. Study results suggest that tillage erosion be included with water and wind erosion estimates when developing spatial maps that reflect a field's erosion history. Spatial maps depicting a field's erosion history and the primary processes affecting erosion could be used for site-specific implementation of conservation practices such as cover crops, organic matter additions, and no-till, which could be targeted at specific erosion processes. [ABSTRACT FROM AUTHOR]