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Nitrate (NO 3 ) 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 provides 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 systems. 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 NO 3 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 MRB and would contribute greatly towards meeting the national goal of significant reduction in NO 3 -nitrogen (N) load entering the Gulf.Key words: adoption-cover crops-hypoxia-Mississippi River-nitrate leaching-water quality Nitrate (NO 3 ) in surface waters of the Mississippi River Basin (MRB) degrades freshwater quality in the region and much of it is eventually transported to the Gulf of Mexico where it contributes to hypoxia (Rabalais et al. 1996). Agricultural land devoted to corn (Zea mays L.) and soybean (Glycine max L.) production in the Upper Midwest makes a major contribution to NO 3 found in surface waters (Burkart and James 1999; Goolsby et al. 2001;David et al. 2010). Alexander et al. (2008) estimated that over 50% of the nitrogen (N) fluxes from the Mississippi River originated from agricultural land producing corn and soybean. In addition, artificial drainage systems used primarily for corn and soybean production increase losses of NO 3 from agricultural land (Goolsby et al. 2001;Royer et al. 2006) by accelerating transport to surface water (Zucker and Brown 1998) and bypassing subsurface flow paths that would reduce NO 3 concentrations through denitrification or other processes (Schilling et al. 2007). As a result, five upper midwestern states (Iowa, Illinois, Indiana, Ohio, and Minnesota), which have large areas of artificially drained land used for corn and soybean production, contribute about 46% of the NO 3 -N load to the Mississippi River that re...

A fall-planted winter cover crop is an agricultural management practice with multiple benefits that may include reducing nitrate (NO 3 ) 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 NO 3 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 variables 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 NO 3 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.

electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Cover Crop PreferenceTh e survey found that cover crop use in the Corn Belt was low. Only 11% of Corn Belt farmers had planted cover crops in the period between 2001 and 2005. And only 8% had planted cover crops in the fall of 2005. Plants used as cover crops varied somewhat among the four states (Table 1). In Indiana and Illinois, cereal rye, wheat, and red clover were the most popular choices. In Iowa, cereal rye and oat were the top two choices among farmers. In Minnesota, oat was the dominant choice. Minnesota farmers also listed other cover crops, not included in these choices, as a large percent (21%) of the cover crops they used. Th e results from these states indicate that farmers use multiple cover crops on the land they manage. Furthermore, the cover crops used follow from the major fi eld crops planted in these states. For example, in 2006, Illinois and Indiana had 376,500 and 190,200 ha of winter wheat, compared with 10,121 and 20,243 ha in Iowa and Minnesota. Farmers in Illinois and Indiana are more familiar with winter wheat and may use some of the saved seed. Red clover use was also higher in these two states, which likely results from interseeding red clover in winter wheat. ABSTRACT Surveying end-users about their use of technologies and preferences provides information for researchers and educators to develop relevant research and educational programs. A mail survey was sent to Corn Belt farmers during 2006 to quantify cover crop management and preferences. Results indicated that the dominant cereal cover crops in Indiana and Illinois are winter wheat (Triticum aestivum L.) and cereal rye (Secale cereale L.), cereal rye and oat (Avena sativa L.) in Iowa, and oat in Minnesota.Legumes were used more frequently in Indiana and Illinois, and red clover (Trifolium pratense L.) was the dominant choice across the region. Farmers relied solely on herbicides 54% of the time to kill cover crops. Ninety-three percent of respondents indicated that they received no cost sharing for using cover crops and 14% indicated that they would plant cover crops on rented land. Corn Belt farmers prefer cover crops that overwinter (68%) and fi x N (64%). Th e information provided in this survey supplements existing knowledge that can be used to develop relevant research and educational programs to address agronomic production systems that include cover crops.