Yield tradeoffs and weed suppression in a winter annual oilseed relay-cropping system

Authors: HOERNING, CODY - University Of Minnesota; WELLS, M - University Of Minnesota; Gesch, Russell - Russ; FORCELLA, FRANK - Retired ARS Employee; WYSE, DONALD - University Of Minnesota

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2019
Publication Date: 6/12/2020
Citation: Hoerning, C., Wells, M.S., Gesch, R.W., Forcella, F., Wyse, D.L. 2020. Yield tradeoffs and weed suppression in a winter annual oilseed relay-cropping system. Agronomy Journal. 112(4):2485-2495. https://doi.org/10.1002/agj2.20160.
DOI: https://doi.org/10.1002/agj2.20160

Interpretive Summary: The Upper Midwest Corn Belt region of the US is dominated by just two crops: corn and soybean. These are grown as summer annuals. After harvest, the soil remains bare and exposed to erosion from fall to the following late spring/early summer. The winter annual oilseeds: pennycress and winter camelina can be grown as cover crops and fill the void between the production of corn and soybean and offer environmental benefits such as reduced erosion and weed suppression. Also, both winter oilseeds can be relay-cropped (i.e., inter-seeded) with soybean to produce two crops in a single season. This research was conducted across three sites in Minnesota to evaluate the ability of these winter oilseeds to suppress weeds and study the effect of light competition on soybean yields in relay-cropping systems. Pennycress was found to suppress weeds by 97 to 100% while winter camelina suppressed weeds from 85 to 87%. The more that light quantity was reduced to soybean below the winter oilseed canopy and greater the number of days that soybean grew below the oilseed canopy, the greater the yield decline was in relay-cropped soybean. At two of the sites, soybean yields were reduced by competition with the winter oilseeds. However, at one of the sites, the total seed production (winter oilseeds plus soybean) was increased by 20% as compared to growing a single crop of soybean. This information will benefit crop growers, extension specialists working with farmers to adopt this new system, agricultural consultants, weed specialists and conservationists.

Technical Abstract: Midwest crop production is dominated by two summer annual crops grown in rotation, corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. The rotation leaves a productivity gap during the spring and autumn. Winter oilseed crops, such as pennycress (Thlaspi arvense L.), and winter camelina [Camelina sativa (L.) Crantz], can fill this gap and provide ecosystem and economic benefits. The objectives of this study were to: i) evaluate corn and soybean yields in a relay cropping rotation involving both winter oilseed crops, ii) examine competition and tradeoffs between soybean and winter oilseed yields, and iii) evaluate the weed suppression ability of the winter oilseeds. Three sites were used across south and central Minnesota to evaluate winter oilseeds and commodity crop yields in a relay-cropping production system. Soybean yield was reduced at two of the three sites by the winter oilseed treatments. Corn yield, in the subsequent year, was unaffected by the winter oilseed treatments. At one site, total oilseed production (winter oilseed crop + soybean) was increased by 20%, while at the other two sites, there was no significant difference. Light quantity under the winter oilseed canopy and days of soybean-winter oilseed competition affected soybean yield. Weed populations were suppressed by inclusion of the winter oilseeds. The pennycress treatment suppressed early season weeds by 100% and 97% for both sites. Likewise, the camelina treatment reduced weeds by 85% and 87%. The inclusion of winter oilseeds in the corn-soybean cropping system can increase overall production and suppress early-season weeds.