The Agronomic Factors You Need to Weigh Before Rotating in 2021

Any farmer knows what works for one field or crop won’t necessarily work for another. Agronomic factors influence every crop decision — everything from farming practices to geographic considerations like soil type, slope and weather can impact what works in your fields. Pioneer has been studying regional crop rotation for decades, so we asked Pioneer Agronomy Manager Matt Essick and Harley Janssen, Corteva Digital Business Manager, to weigh in on the corn vs. beans debate.

Harley Janssen, Corteva Digital Business Manager
Matt Essick, Pioneer Agronomy Manager

“Finding the right product for the right acre is a real thing. You have to keep in mind that wrong product, wrong acre is going to set your operation back not only for just the next season, but for years. Product selection and placement is really significant,” said Essick.

Yield Potential and Disease Risk

In any crop decision, Essick recommends starting with yield potential and risk of disease.

“Typically, you’ll see a yield drag on corn-on-corn acres of about 5 to 15 percent,” he said. In 2020, however, some farmers experienced a drag of closer to 20 percent — adding fuel to the corn vs. beans debate. 

“We entered 2020 with more residue than usual,” said Essick. “With a cooler 2019 fall, we just didn’t get as much tillage done to break down the residue. When you add in inadequate August rainfall in the corn belt, we slowed down the mineralization of nitrogen in the soil. So it was kind of a one-two punch for corn-on-corn in 2020.”

Disease is the largest risk for continuous cropping. The advantage to a corn-soybean crop rotation is that most diseases impacting the corn crop are allowed to die off while soybeans grow the next season, and vice versa. When planting the same crop year over year, diseases that overwinter in the soil have an opportunity to return the next year with a vengeance.

Diseases to watch for in a corn-on-corn rotation

  • Seed and seedling rot: A number of fungi that survive in crop residue thrive in the cool, wet weather of early spring. These will target corn seeds and seedlings as they emerge.
  • Foliar diseases: Even developing corn can be susceptible to fungal diseases carried over from crop residue. Wet conditions at any point during the growing season can provide ideal conditions for anthracnose leaf blight, gray leaf spot, northern leaf blight, and eyespot. 
  • Stalk rot and ear rot: As harvest approaches, it’s especially important to watch for rot in the stalks and ears when growing corn-on-corn crops. A wet autumn can result in ideal conditions for overwintered fungi.

Additional corn-on-corn considerations

Nitrogen Requirements and Expense

Another key consideration in the argument for corn vs. beans is the nitrogen requirements and expenses. Here’s what Essick and Janssen recommend growers keep in mind:

  • More nitrogen for corn: A major advantage to the corn-soy rotations is that soybeans have less residue and a lower carbon to nitrogen ratio. This allows the residue from soybeans to break down quicker and release nitrogen faster through mineralization. Essick says this can amount to around 30 to 50 pounds per acre more nitrogen in most scenarios.
  • Think outside the box: Janssen says that there’s an opportunity to be creative in your corn-on-corn nitrogen management practices. “Use a cheaper application such as anhydrous with a stabilizer in the fall or spring and then a variable rate shot later in the season.” A Granular Agronomy CSA can help fine-tune a nitrogen strategy customized to your rotation and N needs.
  • Time it right: Nitrogen is the most critical nutrient for corn yield. But ultimately, it’s the timing of your application that matters more than the variability. Janssen recommends turning to your agronomist or CSA for advice.
  • Pick the right acres: Nitrogen is extra hard to manage on extremely wet or dry soils. In these situations, Essick warns against throwing more stress at it, like a corn-on-corn rotation would. Instead, go with your best laying field and most productive soils.

Tillage, Harvest Logistics and Capacity

Don’t forget to factor in additional related costs from continuous crop rotations, warns Janssen.

For corn-on-corn, you’ll need intensive tillage to bury crop residue and upper soil layers. Excess residue can house diseases over the winter, as well as herbicide-resistant weeds. You’ll also want to make sure residue isn’t impeding your seed to soil contact, which can impact germination in the spring. Depending on your exact needs, extra tillage on corn-on-corn can cost between $14 to $21 more per acre

With a second-year corn crop, possible early harvest also means increased drying costs. And more corn equals more labor to get it out of the field and more bushels to store. If you don’t sell out of the field or have your own storage, you’ll need to factor in the cost to store those bushels at an elevator or in a ground pile. 

“It’s never as simple as yield x price when you’re making these decisions,” said Janssen. “You need to look at the full story and all the variables, and those are different for every operation.”

Your local Pioneer seed rep is a great place to start. Reach out to them today for help deciding the right fit for your acres in 2021.

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