Nitrogen management is never a one-size-fits-all program. Every field is different, and the right fertilization plan depends on your soil, the crops you grow, and the fertilizer you use.
One of the biggest differences comes down to crop rotation. Continuous corn often needs more nitrogen because of heavy residue and how it affects nutrient availability. But if you rotate corn with soybeans, nitrogen needs and costs can be reduced.
Understanding the intricacies of these two systems can help farmers make smart decisions that protect yield and their bottom line.
Nitrogen dynamics after corn vs soybean crops
Corn
On average, a bushel of corn will contain about 0.6 lbs of nitrogen. So the grain in a 200-bushel harvest will remove 120 lbs of nitrogen from the soil. However, many farmers know they must apply a lot more than 120 lbs of nitrogen, as much of it will remain in the corn residue that stays in or on the soil. There’s roughly 50 lbs of corn residue remaining in the field for every bushel of corn harvested, and that residue can tie up nitrogen within its organic matter.¹ This ultimately reduces the amount of nitrogen in the soil needed for the next crop. Additionally, an abundance of corn residue will keep soils cooler and wetter, which can hinder the microbial activity needed to break down any corn residue left behind.
Heavy rains right after planting corn can wash 1-5% of your nitrogen fertilizer below the root zone, making it harder for corn to reach. On top of that, saturated soils can lose even more nitrogen through denitrification, especially if the soil is warm. That’s why some growers hedge their bets with split applications or in-season sidedress, just to make sure the crop gets what it needs when it needs it.²
Soybean
Many farmers rotate soybeans after corn because soybeans add nitrogen to the soil. While soybeans have the unique ability to fix nitrogen from the air, they actually require more nitrogen than corn.
Harvested soybeans contain about 5.3 lbs of nitrogen in each bushel, but the plants fix only 50% of that nitrogen. In total, soybeans are pulling more nitrogen from the soil than they add back in. However, the nitrogen contained within their roots, nodules, and leaf litter will break down and release nitrogen back into the soil.³
Unlike corn residue, soybean residue has a lower carbon-to-nitrogen ratio, which means it decomposes faster and doesn’t tie up nitrogen in the process.⁴ This quicker breakdown helps release more nitrogen in time for the next crop, making it a helpful boost to corn, especially early in the season.
Nitrogen management considerations
After corn
If you continuously plant corn on corn, you’ll have a different nitrogen management plan than if you rotate with soybeans. Continuous corn requires 30-50 more pounds of nitrogen per acre than a soybean rotation.⁵
After soybean
Even with some nitrogen being tied up by soybean residue during early breakdown, years of research show that applying about 30% less nitrogen after soybeans (compared to corn-on-corn) can still boost corn yields by 10 to 15 bushels per acre.⁶
How to calculate N needs
Given unpredictable weather conditions, should you apply nitrogen before planting or wait for in-season application? A combination of the two strategies may work best. Applying a base rate of nitrogen fertilizer before planting, followed by applications during the growing season, can improve your nitrogen use efficiency.⁷
A tool like the Corn N Rate Calculator can help you better decide how much fertilizer to apply upfront based on different field conditions and fertilizer prices.⁸ The calculation is based on the Maximum Return To Nitrogen, or MRTN, which looks at how corn usually responds to various amounts of nitrogen, the cost of fertilizer, and the price of corn. This helps farmers determine how to make the most money from their fertilizer program — not necessarily the highest yields.⁹
Test for soil nitrate before planting
Testing your soil for nitrate levels before planting can help fine-tune your nitrogen rates, an especially worthwhile step when fertilizer prices are high. A spring nitrate test gives you a good idea of how much nitrogen is already in the soil, so you’re not applying more than you need. It’s helpful in areas that have been affected by droughts, where there is a substantial amount of nitrogen carryover in the soil.¹⁰
Weather
Weather can make or break your nitrogen plan. Warm winters and early springs can speed up mineralization, meaning more nitrogen becomes available naturally. That might mean you can get by with less fertilizer than you thought.
But weather can also cause losses. Leaching, denitrification, and volatilization can rob nitrogen before plants ever get to it.
Tools like the late spring nitrate test (LSNT) can help estimate in-season nitrogen needs. To minimize losses, the most efficient time to apply nitrogen is just before the V6 stage. If you apply earlier in the season, using anhydrous ammonia can reduce the risk of nitrogen loss because it stays in the soil longer before converting into a form that can leach away.¹¹
Making the right nitrogen decisions starts with knowing how your crop rotation affects the soil. By tailoring your nitrogen strategy to fit your field conditions, you can stretch your fertilizer dollar further and set your corn up for success.
Experts are available to help you make your nitrogen management decisions. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.
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Endnotes
- Lardy, Greg. “Make the Most of Corn Residue.” North Dakota State University Agriculture Communication, 2 Oct. 2008, https://www.ag.ndsu.edu/news/newsreleases/2008/oct-2-2008/make-the-most-of-corn-residue.
- Quinn, Dan. “Should Supplemental Nitrogen be Applied to Corn following Heavy Rainfall?” Purdue University Department of Agronomy, 2 July 2021, https://ag.purdue.edu/news/department/agry/kernel-news/2021/07/supplemental-n-corn-heavy-rain.html.
- Temple, Laura. “Residue Affects Soil Nitrogen Cycling and Crop Yields.” Soybean Research & Information Network, 3 Apr. 2023, https://soybeanresearchinfo.com/research-highlight/residue-affects-soil-nitrogen-cycling-and-crop-yields/.
- Zoubek, Gary, and Aaron Nygren. “Giving Proper Nitrogen Credit to Legumes in Corn and Milo Rotations.” CropWatch, University of Nebraska–Lincoln, 27 Oct. 2008, https://cropwatch.unl.edu/giving-proper-nitrogen-credit-legumes-corn-and-milo-rotations.
- Licht, Mark. “Considerations for Continuous Corn.” Integrated Crop Management News, Iowa State University Extension and Outreach, 18 Nov. 2019, https://crops.extension.iastate.edu/cropnews/2019/11/considerations-continuous-corn.
- Temple. “Residue Affects Soil Nitrogen Cycling and Crop Yields.”
- Iqbal, Javed, Richard Ferguson, and Bijesh Maharjan. “How Can a Warm Winter and Spring Affect Nitrogen Availability for the Upcoming Crop?” CropWatch, University of Nebraska–Lincoln, 3 Apr. 2024, https://cropwatch.unl.edu/2024/how-can-warm-winter-and-spring-affect-nitrogen-availability-upcoming-crop/.
- Mallarino, Antonio. “Considerations for Spring Preplant Nitrogen Application to Corn with High Fertilizer Prices.” Integrated Crop Management News, Iowa State University Extension and Outreach, 5 Apr. 2022, https://crops.extension.iastate.edu/cropnews/2022/04/considerations-spring-preplant-nitrogen-application-corn-high-fertilizer-prices.
- “Maximum Return to Nitrogen (MRTN) Approach.” Ohio State University Extension, https://agcrops.osu.edu/node/4423.
- Mallarino. “Considerations for Spring Preplant Nitrogen Application to Corn with High Fertilizer Prices.”
- Camberato, Jim, R.L. (Bob) Nielsen, and Dan Quinn. Nitrogen Management Guidelines for Corn in Indiana. Purdue University Department of Agronomy, Apr. 2022, https://www.agry.purdue.edu/ext/corn/news/timeless/nitrogenmgmt.pdf.
