Harness More Solar Power

Plant multiple hybrids, based on leaf structure and soil type, to capture more energy.
With the advent of multi-hybrid planters, in addition to GPS and variable-rate applicators, you now can plant the ideal hybrid on every type of soil you farm and manage each one for top yield. But which hybrid should go where? Leaf structure is one of the most important factors you need to understand to match hybrids to soil management zones, says Farm Journal Field Agronomist Ken Ferrie.

“A plant’s leaves capture sunlight, the energy source that drives growth and yield,” he explains. “Through the miracle of photosynthesis, plants use the sun’s energy to convert carbon dioxide, water and nutrients into starches, sugars and, ultimately, grain.

“To maintain constant growth, plants must produce more starch during daylight hours than they can burn during an entire 24-hour period. If the plant runs short of starch, it will begin to cannibalize itself, transferring starch from older parts of the plant to the newer, growing parts. This creates stress, which can be detrimental to yield,” he adds.

As water is pulled through plants by transpiration, nutrients are carried along with it. Energy from the sun drives the process in which water and nutrients are turned into starch. But sunlight hitting the ground is wasted—worse than wasted because it causes evaporation of water that will not be available to plants.

“You can’t change the amount of sunlight hitting the crop,” Ferrie summarizes. “But you can change how much light you intercept.”

You can increase light interception by increasing leaf area index (LAI). LAI compares the area of leaf surface to the area of soil surface. For example, an LAI of 4.0 means there’s 4 sq. ft. of leaf surface area for every 1 sq. ft. of soil surface—or enough leaves to cover the soil surface four times.

Depending upon a variety’s branching characteristics, soybeans close their rows at an LAI of 4.0 to 6.0. But with corn, row closure is affected by both leaf type and LAI.

“With a fully upright-leaf hybrid, whose leaves point straight up, you can have an LAI of 6.0, but sunlight will still reach the soil surface,” Ferrie says. “In comparison, a pendulum-leaf hybrid that is growing rapidly because of good management practices and starter fertilizer might reach full canopy at an LAI of 4.0.”

Anything you can do to increase LAI is beneficial, Ferrie says. The more sunlight plants capture, the more water they transpire and the more nutrients they turn into starch. Sunlight capture and water transpiration are maximized when the crop canopy closes.

You don’t need to measure LAI to determine if you’re maximizing light interception. Just look beneath the canopy of soybeans or corn midday, and see how much sunlight is reaching the soil surface.

You want to reach full canopy, and capture at least 97% of the sunlight with the plant’s leaves, as quickly as possible. “Your opportunity to capture more sunlight ends with tasseling because the corn plant will not put on anymore leaves after that point,” Ferrie says.

If you’re not achieving that goal, there are several ways to increase light interception. Although you can’t achieve full canopy when the crop is knee high, applying starter fertilizer might produce faster growth and larger plants with more leaf coverage.

“With corn, increasing leaf area by achieving faster plant growth pays off until tasseling time,” Ferrie says. “At that point, when there are no more leaves coming out, LAI has peaked, and it soon will begin to go down as the plant cannibalizes lower leaves.”

Eliminating restricting soil layers, or compaction, will also help plants grow faster. Lastly, you can increase population, or plant density. If plants shoot suckers or put on multiple ears, your population is likely too low.

“That suggests plants are receiving surplus sunlight, and producing starch faster than they can burn it,” Ferrie says. “In contrast, soybeans that receive excess sunlight will continue to branch until they close the canopy.”

Once you capture 97% of the sunlight, increasing population with that variety or hybrid will not increase yield. “In fact, it might decrease yield because there’s no more energy for the plants to use, and each one will receive less water and fewer nutrients,” Ferrie says.  

“Another way to increase leaf area and light interception, which is now possible with variable-input technology, is to plant hybrids with two types of leaves,” Ferrie says. Leaf structure has evolved through the years.   

“Older hybrids, with wide leaves in horizontal format, were designed to capture all of the available sunlight in wide rows and at lower populations,” Ferrie explains. “They succeeded in capturing sunlight at lower populations, but they put in a yield ceiling.

“Once all of the sunlight has been captured, water transpiration plateaus. If the crop has been transpiring ¼" of water per acre per day at 36,000 plants per acre, it will transpire about the same amount at 40,000 plants per acre. Increasing the population will only increase plant stress because less water and fewer nutrients are available for each plant.”  

Plant breeders realized they had to increase sunlight interception and starch production to increase yield. “To do so they introduced more upright leaves, especially at the top of the plant,” Ferrie says. “That let more sunlight reach the lower leaves. The upright-leaf plants broke through yield plateaus.

“Now you can buy hybrids with pendulum-type, upright or almost any leaf combination,” Ferrie says. “But seed companies have no standard nomenclature for leaf type, so you encounter many terms, such as open, closed upright and pendulum.”

Ferrie and his staff group hybrid leaf types as pendulum, semi-pendulum, semi-upright and upright:

  • Pendulum leaves are parallel to the ground. Pendulum-leaf hybrids tend to be tall, and the flag leaf is parallel to the ground. Tassels are high, above the canopy—easy to see when driving down the road.
  • In semi-pendulum hybrids the top three or four leaves are upright and the rest are pendulum.
  • Semi-upright hybrids will have pendulum-type leaves to the ear and upright leaves on the rest of the plant.
  • Upright-leaf hybrids have upright leaves from top to bottom. The top two leaves are parallel with the tassel, almost hiding the tassel from the road. They tend to be shorter in stature.
The easiest way to identify hybrid leaf types is to plant a hybrid plot. “Use a hybrid you’re familiar with as a ringer, or check hybrid,” Ferrie says. “After pollination, when all leaves are present and the plant has finished growing, but before leaves are lost through senescence, cut some stalks at ground level. Carry the plants out of the plot, without damaging the leaves. Stand the plants up next to a building and compare the ringer and other genetics for height, leaf structure and tassel type. Take pictures for future reference. After you study hybrids this way, the differences in leaf type will become clear.”

Use your knowledge of leaf types to select hybrids and place them in the right management zone. “Upright-leaf plants tend to harvest more sunlight and push yield higher,” Ferrie says. “Some of our highest corn yields have come from more upright genetics.

“Letting more sun into the canopy increases the evapotranspiration rate, so plants use more water. The canopy gets warmer. Place upright-leaf hybrids on soils with good water-holding capacity and high yield potential,” he adds.

If upright-leaf hybrids don’t have enough water to sustain high evapotranspiration rates, they can burn up, Ferrie cautions. For example, during the drought in central Illinois in 2012, some fields of upright hybrids yielded zero bushels.

Pendulum-leaf hybrids belong on light, droughty soils where water is likely to run short. “They let you lower the population and use less water, which is the limiting factor on these soils, while capturing all the sunlight,” Ferrie says. “During the 2012 drought, pendulum-leaf hybrids sometimes yielded 150 bu. per acre, while upright-leaf hybrids in the same field yielded nothing. The canopies in the pendulum-leaf hybrids were 10°F cooler in the daytime than the canopies of the upright-leaf hybrids.”

Understanding leaf type can prevent costly mistakes. “Based on drought-year yields, some growers cut back on upright-leaf hybrids and planted more pendulum-leaf varieties the following season,” Ferrie says.

“In 2013 and 2014, water was plentiful. Hybrids that died from lack of water in 2012 kicked yield out of the park. Pendulum-leaf hybrids yielded well, but they couldn’t keep up with the more upright-leaf genetics. Those farmers dropped good hybrids after only one season because they didn’t realize they were placed incorrectly for the growing conditions,” he adds.

When you understand leaf type, you’re ready to implement the final step in variable-input technology: the ideal hybrid on every soil type.

Matching Leaf Type and Row Width

Forgetting that upright-leaf hybrids fit high-yield environments and pendulum-leaf hybrids maximize yield on sandy, droughty soils is a recipe for disaster, says Farm Journal Field Agronomist Ken Ferrie. One aspect of the environment is row width.

“Pendulum-leaf hybrids were designed to capture all the sunlight when planted in wide rows,” says Farm Journal Field Agronomist Ken Ferrie. “If you plant pendulum-leaf hybrids in narrow rows (twin, 20" or 15") and push the population, yield will likely go backward. The only time to use pendulum-leaf hybrids in narrow rows is when you’re trying to protect a low water supply by planting an ultra-low population, such as 18,000 plants per acre, in dryland corners of an irrigated field.”

Conversely, upright-leaf hybrids will fail where water is limited. “As soon as leaves begin to roll, light interception is reduced and starch production falls,” Ferrie explains. “If this goes on long, the plant starts to cannibalize itself. Any stress reduces yield potential.”

Some hybrids are so upright in leaf structure it’s impossible to plant them thick enough in wide rows to capture all the sunlight, Ferrie adds.

“They are designed for narrow rows, when you’re trying to capture all the sunlight by pushing plants closer together,” he says.

Tools are available to vary the rate of every input for every soil type in a field. Ready yourself for variable-input technology by following along with this seven-part series at bit.ly/VIT-series

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