Agronomy and Horticulture, Department of


First Advisor

Christopher Proctor

Date of this Version



Wehrbein, J.S. 2019. Integration of cover crops into Midwest corn-soybean cropping systems and potential for weed suppression. M.S. Thesis. University of Nebraska, Lincoln.


A THESIS Presented to the faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agronomy, Under the Supervision of Professor Christopher A.Proctor. Lincoln, Nebraska: December 2019.

Copyright (c) 2019 Joshua S. Wehrbein


Cover crops have potential to provide benefits to agricultural systems, such as improved soil productivity, nutrient scavenging, weed suppression, and livestock forage. There are several challenges associated with cover crop integration into traditional Midwest corn-soybean cropping systems. One of these challenges is timely establishment in the fall, which is limited by the relatively late harvest of corn and soybean. Cover crop effectiveness is related to the amount of biomass produced, thus maximizing the growth period in the fall is desired. To address this challenge, we evaluated the potential to utilize early-season soybean maturity groups (MGs) to allow for earlier soybean harvest and cover crop planting to maximize cover crop growth. In addition, an integrated cover crop and herbicide management program was evaluated to determine its effect on weed suppression and corn yield. Cover crops have often been shown to be most effective when integrated with other methods of weed management such as herbicides. Cover crops have also been shown to potentially reduce subsequent corn yield. Therefore, we evaluated the influence of cover crop planting date, termination date, and herbicide program on weed density, weed biomass, and subsequent corn yield. Field experiments were conducted in 2017-2019 across six different locations in Nebraska, Ohio, and Kentucky. Results suggest use of early-season soybean MGs allow cover crops to be planted up to 30 days sooner than late-season MGs. Cover crop biomass production was highest for early cover crop planting dates associated with early-season MGs across most site-years evaluated. Soybean yield often plateaued near a 3.0 relative maturity (RM) depending on the region, suggesting that soybean RM may be reduced to 3.0 to allow for earlier cover crop planting without sacrificing soybean yield. Results further suggest that use of a residual herbicide with a postemergence herbicide was necessary to obtain the largest reduction in both weed density and biomass. Weed biomass was occasionally reduced by the cover crop, however, results were inconsistent. Cover crops generally had minimal influence on overall weed suppression, and occasionally resulted in corn yield reduction, indicating the importance of other traditional methods of weed management.

Abbreviations: MG, maturity group; RM, relative maturity.

Advisor: Christopher A. Proctor