Jon Zuk, agronomist
Most agronomists would agree that rotating crops is a practice that can help maximize a seed’s genetic yield potential. But market conditions and on-farm needs mean that some farmers are choosing to skip the rotation and opt for continuous cropping plans instead. As you think about seed purchases for next season, keep in mind how your crop rotation and associated management practices could impact yield potential.
What’s the yield penalty?
Research published in Agronomy Journal in 2017 reported that rainfed fields across the Midwest suffered an average 4.3 percent yield penalty in continuous corn production and a 10.3 percent yield penalty in continuous bean production during the 2007 to 2012 growing seasons.1 The study also showed that the yield penalty for corn grew with up to three years of continuous cropping, but then leveled off. But for soybeans, the yield penalty continued to increase over the number of years continuously cropped.
There are many factors that likely contribute to the yield reduction in a continuous crop rotation. One of the biggest impacts is the increase in insect and disease pressure in the absence of crop rotation. When acres are rotated, this can disrupt the life cycles of insects, diseases or weeds. As you consider your cropping plan, here are some specific actions you can take to limit potential yield penalties.
Corn-on-corn: Hybrid selection and placement is key
Research has shown that continuous corn yield penalties are more severe in areas with low moisture and low yields.1 With that in mind, it makes sense to choose high production acres for corn-on-corn rotations, if possible. When choosing hybrids for continuous corn acres, strive to find balance with a high-yielding hybrid that also carries defensive traits like strong disease and insect resistance. Trait packages that protect against above- and below-ground pests, including corn rootworm, are also a good investment for corn-on-corn acres. Seed treatments can protect against early-season fungal diseases and insects that might be more prevalent due to the extra plant residue and added moisture in continuous cornfields.
Other management practices that can help limit the yield penalty include:
- Examining tillage. A 2015 study published in Agronomy Journal found that the economic return for conventional tillage systems in a corn-on-corn rotation in Iowa was 11.1 percent higher than in a no-till system.2
- Applying foliar fungicides. As pathogen populations accumulate in soil and crop residue, the potential for disease infection and severity increases.
- Managing corn residue. Extra residue can result in additional challenges at planting, including wetter, cooler soils. Excess corn residue can also have implications for nitrogen cycling.
Soybean-on-soybean: Manage for pests
While there are similar considerations for continuous corn and continuous soybean acres, pests seem to be one of the biggest yield-limiting factors in soybean-on-soybean fields. Soybean cyst nematode (SCN) is historically one of the main concerns, although many farmers aren’t testing for the pest in their fields. Research conducted by Ohio State University shows that annual losses from SCN can exceed one billion annually in the United States.
Growers planting soybeans back-to-back should choose varieties with resistance to SCN and should also consider the source of those resistant genes. Iowa State University reports that there are over 1,000 SCN-resistant soybean varieties on the market, but more than 97 percent of those derive their resistance from the same breeding line, PI 88788. As of last year, there were fewer than 30 soybean varieties available with SCN resistance from sources other than PI 88788, which means SCN populations are becoming more difficult to manage in some states.
As growers with continuous soybeans select their seed, they should consider rotating to varieties that don’t have the same disease weaknesses or herbicide tolerances as the previous year’s crop. Alternating genetics can help bring diversity to your crop production program so that common weed, insect and disease pests don’t become resistant to management strategies. WinPak® soybeans from CROPLAN® seed are a unique combination of two varieties that provide an exceptional level of stability throughout the field. WinPak® varieties work together and confer different levels of protection against common diseases to help mitigate risk.
Seed treatments are another important consideration for continuous soy acres. Diseases including rhizoctonia, Pythium and sudden death syndrome can infect plants early in the season, leading to substantial stand and yield loss. Selecting soybean varieties with the right seed treatments can provide up to 40 days of protection against those early-season diseases.
Other considerations to reduce the yield penalty of continuous soybean planting include:
- Watching nutrient availability. Multiple years of soybean production can remove nutrients such as phosphorus and potassium from the soil. Higher-yielding varieties require more fertilization to meet the seed’s genetic potential. Soil and tissue sampling can help gauge whether your fertility plan is sufficient for your crop’s in-season needs.
- Applying foliar fungicide and insecticide. Because disease inoculum and pest pressure is higher in non-rotated fields, a fungicide and insecticide application at the R2/R3 growth stage can provide extra protection against late-season pests.
Plan for success
While rotating corn and soybeans is still the preferred production practice to maximize yield, making smart management decisions can help reduce the yield penalty for continuously grown crops. Choose corn hybrids and soybean varieties with appropriate resistance against common disease and insect pressure, and manage in-season with foliar fungicide and insecticide applications to reduce pest populations. Talk with your WinField United retailer to learn how tillage, fertility and residue management could impact your yield potential on continuous crop acres.
1. Seifert, C. A., M. J. Roberts, and D. B. Lobell. 2017. Continuous Corn and Soybean Yield Penalties across Hundreds of Thousands of Fields. Agron. J. 109:541-548. doi:10.2134/agronj2016.03.0134
2. Al-Kaisi, M. M., S. V. Archontoulis, D. Kwaw-Mensah, and F. Miguez. 2015. Tillage and Crop Rotation Effects on Corn Agronomic Response and Economic Return at Seven Iowa Locations. Agron. J. 107:1411-1424. doi:10.2134/agronj14.0470
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