We have confidence that all researchers will be able to complete the objectives as outlined. Given that we have four locations, we should have reliable data even if one location has an unforeseen event such as hail damage. The locations span from the normally drier western ND to typically wetter western MN. At least three of the locations are in areas that commonly grow soybeans. The most important results will come in 2015 and 2016 when canola and soybean have been grown back-to-back. Having two cycles of the study should give us a reasonable estimate of the agronomic and financial benefits of soybean and canola in a tight sequence. Crop rotation studies are typically very cumbersome and difficult to conduct. The design of this study is simplified to be able to answer the two questions listed under Objectives.

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Executive Summary
June 30, 2017

Impact of previous crop on soybean and canola yield

Principal Investigator:
Dr. Brian Jenks, NDSU E-mail: brian.jenks@ndsu.edu
North Central Research Extension Center Phone: 701-857-7677
5400 Highway 83 South
Minot, ND 58701

Co-Principal Investigators:
Dr. Nancy Ehlke, Univ. of MN, ehlke001@umn.edu
Dr. Mike Ostlie, NDSU-Carrington, mike.ostlie@ndsu.edu
Dr. Jasper Teboh, NDSU-Carrington, jasper.teboh@ndsu.edu
Bryan Hanson, NDSU-Langdon, bryan.k.hanson@ndsu.edu
Eric Eriksmoen, NDSU-Minot, eric.eriksmoen@ndsu.edu

Some farmers desire to include both soybean and canola in their crop rotation. Some research and farmer experience indicate that soybeans grow just as well on canola ground as on wheat ground. Since both crops are moderately susceptible to sclerotinia stem rot, some farmers have avoided planting them close together in a crop rotation. However, while not ideal from a sclerotinia standpoint, there is some evidence there may be an advantage to growing soybean on canola ground or vice versa. Growers want to know if this synergism is real and, if so, is it great enough to offset the risk of growing two sclerotinia-susceptible crops back to back. This study was designed to test that theory in the northern plains where soybean and canola are commonly grown. If the hypothesis is true, then the main benefit would be potentially higher soybean yields following a profitable canola crop.

The objectives were to: 1) determine if soybean yield is greater following canola than wheat, and 2) determine if canola yield is greater following soybean than wheat.

These objectives were accomplished using a three-year crop sequence to evaluate soybean and canola production grown back-to-back in rotation with wheat. Four crop rotations from 2013-2014-2015 included: 1) Wheat-Wheat-Soybean, 2) Wheat-Canola-Soybean, 3) Wheat-Wheat-Canola, and 4) Wheat-Soybean-Canola. Agronomic data collected were crop yield, test weight, oil content, crop density, and crop height. The second cycle of the study was repeated from 2014-2016.

Results showed no consistent significant difference in yield at any location between soybean grown on wheat ground compared to soybean grown on canola ground. Generally, there were no differences in soybean density, height, test weight, and oil content. Similarly, there was no significant yield difference at any location for canola grown on soybean ground. Canola yield, test weight, height, density, and oil were similar whether canola was grown on wheat ground or soybean ground.

Based on these two rotation cycles, we observed no real advantage or disadvantage from growing soybean on canola ground or from growing canola on soybean ground. Sclerotinia incidence was very low at all locations. This can be viewed as a positive situation for farmers that want to grow both soybean and canola in a rotation with wheat. Based on this information, it appears that farmers can profitably grow soybean and canola in a rotation. However, farmers must monitor for sclerotinia and make the necessary fungicide applications if weather conditions favor sclerotinia.