How to determine if leaves should flop out, ears should flex and more
High-population corn (36,000 to 48,000 plants per acre) planted in narrow rows is perking a lot of farmers’ ears. The foundation of success with high populations is hybrid selection, says Farm Journal Field Agronomist Ken Ferrie.
When choosing a hybrid and population for narrow rows, consider leaf architecture and ear type.
"There are essentially three types of leaves: upright, pendulum and semi-upright," Ferrie notes. "Upright-leaf hybrids grow straight up like a pineapple; in high populations, an upright leaf structure allows sunlight to reach deeper into the canopy to increase photosynthesis. Upright leaves maximize photosynthesis when high populations are planted in narrow rows," Ferrie explains.
"Pendulum leaves are suited for lower populations to decrease water loss by evaporation while maintaining photosynthetic activity. Pendulum-leaf hybrids flop out and intercept sunlight like solar panels, capturing light before it gets down low.
"In semi-upright hybrids, the upper leaves are more upright in structure and the lower leaves more pendulum," Ferrie says.
Along with deciding which leaf architecture is best, look at ear type. "Determinate-ear hybrids change their ear size very little, so you have to plant them at the higher end of the population range to optimize yield," Ferrie explains.
"Flex-ear hybrids will get bigger, given the right agronomic conditions. Semi-flex hybrids flex their size somewhat less than true flex-ear hybrids."
Failing to understand leaf structure and ear types can be costly, Ferrie notes. "In my experience, if you use a flex-ear hybrid in a pendulum-leaf format, high populations will cause the hybrid to flex the opposite direction, and yield will suffer," he says.
Soil and moisture. Consider your unique objectives and growing conditions. "If you have highly productive soil with good drainage, plenty of nutrients and good rainfall or irrigation that’s a racehorse environment for corn," Ferrie says. "You want to maximize interception of sunlight, so you don’t waste any. A short-statured hybrid with an upright leaf lets light through the canopy to maximize photosynthesis for food production. A determinate-ear hybrid allows you to push population as much as possible."
A grower with droughtier soils needs to manage water use while maintaining yield. "He would want a pendulum-leaf hybrid in narrow rows, in order to canopy as quickly as possible and minimize evaporation of water from the soil," Ferrie says. "A flex-ear hybrid would maximize yield on lower populations while conserving water.
"Many growers farm both types of soil in the same field," Ferrie adds. "In that environment, they should use a hybrid with a semi-flex ear type, pushing populations in their heavy soil and pulling back in their lighter ground.
"A semi-upright-leaf hybrid will provide some row shading in the light soil while also intercepting sunlight in the heavy soils. A semi-flex hybrid will maintain ear size at higher populations and flex out to maintain yield at lower populations."
Precisely selecting corn hybrids requires the help of a good seed rep who thoroughly understands a company’s products and knows their traits and genetics, Ferrie notes.
Disease and pests. Several other factors must enter your planning for narrow rows and high populations, Ferrie points out. "The highest yielding hybrid for your situation might not contain enough disease resistance to defend itself," he says. "If you expect disease to be an issue—for example, if you’re in a northern corn leaf blight area—plan to apply a fungicide.
"Hybrids planted in narrow rows at high populations are attractive to tasting insects such as corn aphids and corn borers," Ferrie continues. "If you selected a hybrid for yield potential, it might be the right choice. But you’ll have to scout and be ready to treat if you find a problem."
With high populations, standability might become an issue. "Pushing populations in this situation requires a plan of attack. Make sure you have plenty of harvest capacity. Plan to harvest early and apply a fungicide, if needed," Ferrie says.
Don’t neglect the basics. "Plant at the right time, place seed at the right depth and close the slot," he adds.
"Calibrate your planter meter for your higher population; you might need different brush settings or a different vacuum pressure to get proper singulation. If you use the same settings at 40,000 plants per acre that worked well at 30,000, you might have problems," he explains.
Finally, be sure to apply enough nitrogen for your higher population and yield goal. "As we go from 20,000 to 40,000 plants per acre, high populations are the first to run out of nitrogen," Ferrie says.
You can e-mail Darrell Smith at firstname.lastname@example.org.