Dr. Marcus Jones, Corn Germplasm Technology Development Manager for Monsanto, said the company conducted plant population/row spacing trials at 72 locations across the Corn Belt in 2008. The field trials included over 24,000 comparisons between seed products with YieldGard VT Triple® in-plant insect protection and corn featuring no insect-protection traits.
The trial protocol, he said, included five different seeding rates, ranging from 23,000 to 43,000 seeds per acre, and also compared plant performance in 20-inch versus 30-inch rows.
“Our message about the benefit of elite germplasm and traits allowing farmers to plant at higher populations holds true, but this varied greatly by area last season due to extreme swings in the weather,” explains Dr. Jones. “2008 was a highly unusual weather year in many parts of the Midwest, so some areas saw a greater advantage than others.”
Dr. Jones notes that higher yield potential began to drop off above 38,000 seeds per acre, compared to 36,000 seeds per acre in a similar trial program in 2007. “The curve is going higher,” he says. “At each population level,” he added, “the YieldGard VT Triple corn outyielded hybrids without insect traits.”
Monsanto has made a commitment to help farmers double corn yield potential, while conserving resources by producing crops with one-third less inputs per unit, by 2030. These field trials, called the Advanced Plant Density and Row Spacing Project, are part of this effort as Monsanto works to better understand the interplay among such key factors as good germplasm, biotech traits, seeding rates and placement, and plant populations.
“Little research has been conducted to determine how advanced trait technology and germplasm might influence seeding rates and plant populations until now,” Dr. Jones says. “We are looking for a better understanding of multiple interactions affecting yield.”
In 2008, the field trials determined that corn planted in 30-inch rows yielded more than in 20-inch rows at all plant populations, except in some areas of South Dakota and Minnesota. The optimal plant population for 30-inch rows was 33,000 to 38,000 plants per acre, while the optimal population for 20-inch rows was 38,000 to 40,000 plants per acre.
Corn with the YieldGard VT Triple technology yielded more than corn with just the Roundup Ready® Corn 2 trait at all populations. Corn with the YieldGard VT Triple technology was able to provide increased yield potential with high populations up to 38,000 plants per acre. Corn without that trait was only able to take advantage of increased plant populations up to 33,000 plants per acre.
“This difference is likely due to the ability of corn with the YieldGard VT Triple technology to better handle stresses of certain insect pests and have greater uptake of moisture and nutrients,” Dr. Jones observes.
Dr. Roger Elmore, Professor of Agronomy at Iowa State University, says his data indicates that some Iowa farmers need to increase their seeding rates, especially on highly productive fields. “Five years ago, 30,000 seeds per acres would have been pushing higher populations,” he says. “With genetic advances, farmers should now consider trying at least 32,000 seeds per acre, maybe higher.”
Best-yielding fields – those that historically yield 200 bushels or more per acre – should be able to handle seeding rates of up to 35,000 seeds per acre or even higher, according to ISU research. Super high-yielding environments might call for more than 35,000 seeds per acre, producing a plant population that has to be managed tightly.
“Every farm and field is different, and farmers should keep that in mind when making decisions about pushing higher plant populations,” Dr. Elmore says. “It depends on the environment, soil type and individual field.”
The terms “seeding rates” and “plant populations” should not be used interchangeably. There is a difference between the number of seeds planted per are and the lower-number “final stand”, which represents plant populations and the actual number of plants that make it to maturity.
In general, Jones says that farmers should target fields with high fertility, good drainage and historically strong yields as candidates for increased seeding rates. Monsanto research shows that about 50 percent of farmers have not changed their planting population in the last five years. Leading academics recommend farmers consider planting 5 percent to 10 percent more seed to boost yield potential and return on investment.
“Increasing plant populations is one of the easiest ways to achieve higher yields, since it does not require additional equipment, land and labor costs,” Dr. Jones observes. “Farmers who plant hybrids with leading traits should try a few test strips with higher seeding rates to see for themselves the yield advantage they can experience.”
Peter Thomison, Professor of Crop Sciences at The Ohio State University, notes that according to the National Agricultural Statistics Service, 34 percent of the corn acreage in Ohio in 2008 had corn plant populations exceeding 30,000 plants per acre. This contrasts with 14 percent of the Ohio corn acreage with populations exceeding 30,000 plants per acre in 2006. This change suggests that many Ohio growers are using higher seeding rates to boost yields. “On highly productive soils that consistently
produce yields of 175 bushels or more per acre, final stands of 30,000 to 33,000 plants per acre or more may be needed to maximize yields,” Thomison says.
University of Illinois Professor of Crop Sciences Emerson Nafziger says his data indicate that some Illinois farmers may want to increase their plant populations.
“It helps to think in terms of how many bushels of yield it takes to pay for that last 1,000 seeds,” Nafziger explains. “Growers can increase their plant populations and not have to worry much about it costing them yield. The fact that yields tend to level off and not drop off at plant populations higher than necessary means that it may often be riskier to have too few plants than too many.”
The Illinois professor adds that soils with average yields above 180 bushels per acre should aim to have harvest populations in the 32,000 to 35,000 plants per acre range. “Populations don’t have to be increased a lot for yields to be higher in good conditions,” Nafziger stresses. “When good conditions mean higher yields on less-productive fields, having higher populations can also increase yields.”