Some farmers have applied liquid manure to fields based on intentions to plant corn in those fields. But because rain has delayed corn planting and it's getting too late to plant corn, those farmers now want to switch the field to soybeans. Can they switch to soybeans without worrying about penalties from the Iowa Department of Natural Resources for exceeding nitrogen application limits on the field? The limits are lower for soybeans compared to corn.
"Normally, there's a 100-pound per acre limit on nitrogen applications on soybean fields for crop producers who obtain the nitrogen from liquid manure," says Ken Hessenius, supervisor of the DNR field office at Spencer in northwest Iowa. "But producers who planned to plant corn and applied liquid manure at higher rates may safely switch the crop to soybeans after June 1 without concern about a penalty. That's one small piece of good news during a wet, cold spring that has delayed corn planting."
The 100-pound available nitrogen limit applies to ground where soybeans have been planted, are already growing or will be the next crop growing in the field. The restriction applies to liquid manure coming from livestock facilities that are required to have a manure or nutrient management plan.
If the crop is switched from corn to beans, put a note in your manure nutrient plan
"If the planned crop is switched from corn to soybeans, the producer needs to put a note in the their manure or nutrient management plan about why they applied manure for corn and are now planting beans," Hessenius adds. "That will ensure there are no questions when the DNR inspects their records."
Keep in mind that the 100-pound limit is no longer applicable after June 1 based on the assumption that crop producers may have to make changes in planned crops because of the weather. For more information, see the DNR website at www.iowadnr.gov/afo/.
Resources available for helping you make smarter N application rate decisions
Iowa State University Extension has updated the Corn Nitrogen Rate Calculator. This is an online tool that allows you to determine nitrogen application rates for corn production and is helpful in determining the effect of fertilizer N and corn price on the amount of nitrogen you need to apply per acre.
The Corn Nitrogen Rate Calculator web tool is located here.
The regional publication "Regional Nitrogen Rate Guidelines for Corn" (PM 2015) can be ordered through any ISU county extension office, from the ISU Extension Online Store, or by calling (515) 294-5247. An electronic copy of the publication is available here.The ISU Agronomy Extension Soil Fertility website is available here.