In the valley of the farm economic cycle, producers search for rays of sunlight to light the way to healthier profit margins. One ray might be hitting the soil beneath their soybean plants, says Ken Ferrie, Farm Journal field agronomist.
“Sunlight drives photosynthesis, which drives starch production, which drives yield,” he explains. “If it hits the ground, it is wasted. So, if you’re not already capturing 95% to 97% of the available sunlight by the early reproductive stages (R2 or R3), a few tweaks to your program might increase profit without adding any cost.”
Maximizing sunlight capture requires closing rows as quickly as possible.
“Besides more sunlight hitting the leaves, shading the ground reduces water evaporation, increases transpiration through the plants and aids in weed control,” Ferrie says.
Four factors affect canopy closure: row width, population, plant type and plant height.
1. Row width and population.
“At the same population, narrow rows will close the canopy faster than wide rows,” Ferrie says. “Farm Journal studies consistently show a 5-bu.-per-acre to 7-bu.-per-acre yield advantage for narrow rows over wide rows at the same population. The yield advantage increases during stressful conditions such as drought or stunting resulting from herbicides.”
Higher populations cause plants to compete for sunlight and grow taller. So if you plant in wide rows, pushing population will close the canopy faster.
“This applies even on light, droughty soil,” Ferrie says. “There, with corn, we reduce population to improve water management. But with soybeans, it’s the opposite. We want more plants shading the ground to reduce evaporation and increase transpiration.”
2. Plant type.
Soybean plants come in two types: in-line and bushy. Your grandfather probably called them drill beans and planter beans.
In-line varieties, which have low branching or none, put their pods on the main stem. Bushy types have a certain amount of branches off the main stem. Some keep most of their pods on the main stem, while others divide their pods between the main stem and the branches. Even within the bushy category, some put more pods on the stem and some put more on the branches.
“If any soybeans get stunted in the growing season, they may not close wide rows, resulting in lower yield and weed pressure late in the season,” Ferrie says. “But the risk is greater with in-line varieties.”
Even if an in-line variety has good growing conditions, it still might not close wide rows, lowering yield and increasing late-season weed pressure.
In stressful conditions, varieties that put pods on branches are more subject to pod abortion than in-line types, but if they don’t abort pods they tend to yield more.
“In wide rows on good soil, plant varieties that put more pods on the branches,” Ferrie advises. “In wide rows on light soils that tend to get stressed, plant bushy varieties that keep most of their pods on the main stem.”
3. Plant height.
“When tall soybeans surpass 97% light capture, there is no further yield benefit if they grow taller, and they may lodge,” Ferrie says. “In studies, we have raised more 80-bu. yields with beans a little over knee-high than with beans that were shoulder-high.
“If you are planting a tall variety into good fertility and water availability, pull back on population, so you don’t end up with a lot of vine and lodged plants,” he adds. “If you are planting a short bean in wide rows on lighter soil, push the population a bit, to help the plants grow taller and close the rows.”
Watch Out for White Mold
In general, rapidly closing the canopy to capture all available sunlight is easier in narrow rows, Ferrie says. But there might be one exception: white mold.
“Keeping the canopy open longer, all the way through flowering, helps control white mold by increasing air circulation and lowering the humidity level,” he says. “However, our studies suggest variety selection, planting a lower population and applying fungicides provides better control of the disease than going from narrow rows to wide rows.”
3 Profitable, But Not Free, Practices
These practices carry some cost but almost always pay off, Ferrie says:
Treat your seed for Sudden Death Syndrome (SDS) if you plant soybeans early where SDS is present.
Purchase additional replant crop insurance to minimize risk.
- Fungicide applications break even or show a profit 82% of the time for Ferrie’s clients.
The annual Farm Journal Corn and Soybean College is slated for July 22 and 23. Click here to learn more about this year’s event.
