Harvesting corn stover from irrigated, high-yielding cornfields shouldn't pose a significant problem for soil quality and erosion control.
But the move by corn producers in recent years to bale more corn stover for livestock feed is causing some heartburn among soil scientists. Add to that the extensive cutting of silage on drought-damaged corn this year, and you're hearing more about the need to sustain the multiple benefits of leaving stover on the field.
Corn stover, among other benefits, reduces erosion, increases soil infiltration and soil moisture storage and improves overall soil health.
"The loss of soil organic matter and microbial carbon is one of the biggest disadvantages to stover removal," says Charles Wortmann, University of Nebraska-Lincoln soil scientist.
In the stover harvesting demo on Duane Kristensen's farm in October, the irrigated field yielded 250 bushels of corn per acre. It also is on table-top land with small potential for water erosion. A 250-bushel yield produces about 7 tons of residue, and about half can be removed since that still leaves 3-1/2 tons, soil scientists say.
"This field does have some sand, so to help control wind erosion we flew on annual rye seed as a cover crop on Aug. 28. The rye also should produce some organic matter," Kristensen says.
UNL scientists say stover should not be removed from highly erodible fields and dryland cornfields. "Yields of less than 120 acres per bushel don't produce enough stover to be harvested," says Paul Jasa, UNL engineer.
Wortmann and UNL colleagues list the following factors to consider in how much stover can be sustainably harvested:
•Soil nutrient availability
•Soil organic matter
•Water erosion and runoff
•Soil water availability
It's not easy to estimate the cost of residue removal, with the exception of nutrient losses. Each ton of corn residue, on average, consists of $10.20 in nitrogen value, $3.60 in phosphorus and $13.60 in potassium.
It's recommended that two to three tons per acre of crop stover should be left in a field annually through the use of no-till or conservation tillage. Less is produced if the field is tilled.
For wind and water erosion control, Wortmann agrees that little if any stover should be removed from medium and highly erodible soils and dryland production.
"On soils of low erodibility, leaving 2 to 3 tons per acre for maintenance of soil organic matter should be sufficient to prevent erosion from exceeding 5 tons of soil per acre," Wortmann says. The 5-ton figure is the acceptable soil loss standard set by the Natural Resources Conservation Service.
Many producers with corn-on-corn, mostly under irrigation, complain of difficulty in planting into the heavy residue cover the next spring.
Jasa doesn't necessarily agree. He says that continuous no-till creates enough biological activity in the soil to break down residue. "At the Clay Center field lab, UNL has had corn-on-corn plots since 1976, under furrow irrigation, and the planter can handle the residue."