Fall management options for cornfields that are unharvestable
AMES, IA - Millions of corn acres have been damaged by the derecho on August 10. Unfortunately for some of these acres, harvest will not take place. Decisions regarding fall management options will need to be made in the coming weeks.
To help with those decisions, let’s focus on some key considerations:
- Discing, vertical tillage, or stalk shredding should take place.
- Plan on planting soybeans in 2021 and have a plan to manage volunteer corn.
- Understand the nutrient value of the unharvested corn.
- Planting cover crops is still an option.
Discing, Vertical Tillage, or Stalk Shredding
Discing, vertical tillage, or stalk shredding will reduce the size of residue, speed up decomposition, and also encourage some corn grain to germinate this fall. More germinating this fall equates to less volunteer corn in the spring.
If choosing to disc the field, minimal soil disturbance is recommended in order to avoid potential erosion, prevent soil structure degradation, and assist with better water infiltration. Maintaining residue cover on the soil surface will reduce erosion and help maintain soil moisture reserves by reducing water evaporation from the soil. Looking ahead to planting next spring, soybeans can be forgiving when planted into high amounts of corn residue.
Planting Soybeans in 2021 and Managing Volunteer Corn
High populations of volunteer corn may emerge next spring even after discing, vertical tillage, or stalk shredding this fall. It can be relatively easy to manage volunteer corn in a soybean field, however, a late flush of volunteer corn may emerge if the soybeans are preceded with a cereal rye cover crop.
Be aware of what corn herbicide traits were used this year, what traits will be used in 2021 during planting, and make any needed adjustments to your herbicide program. It is recommended to avoid planting corn following corn if severe damage has occurred in the field. This is because the volunteer corn will be difficult to manage since it is also selective to corn herbicides. Additional information can be found in the CROPWATCH article Control of Volunteer Corn in Soybean and Corn, from the University of Nebraska-Lincoln.
Understanding the Nutrient Value of the Damaged Corn
When corn plants are broken off and die, and not removed or grazed, certain amounts of phosphorus (P) and potassium (K) remaining in the field will be available for next year’s crop. The content value of P and K varies by what reproductive stage the corn was in, its productivity or yield level, and the growing conditions throughout the year. Nitrogen (N) remaining in non-harvested corn plants will cycle through the soil system.
When planted into soybeans the following year, changes in N cycling won’t affect the soybean crop. If planted back into corn the following year, there is the potential for higher-than-normal amounts of mineralized N to be available. However, this takes into account rainfall amounts and other factors that may influence N mineralization from late summer till next spring. Additional information can be found in the ISU Extension and Outreach ICM News article Wind Damaged Corn – Nutrient Content?
Planting Cover Crops is Still an Option
Successfully planting cover crops this fall in fields that are not harvested will greatly depend on increasing seed-to-soil contact and reducing the size of the corn residue. Both of these can be accomplished through discing, vertical tillage, or stalk shredding. Drill seeding may also be considered for planting. No matter which planting method is chosen, seeding should be delayed until rain is forecast. Cereal rye is the most popular cover crop species and should be used because of its overwintering benefits.
Mark Licht is an assistant professor and Extension cropping systems specialist with Iowa State University Extension and Outreach.