Search

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]

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]