A DuPont Pioneer survey last year shows about 30% of the corn acres in North America are currently planted between 30,000 and 33,000 seeds per acre. However, the fastest growing category is 33,000 to 36,000 seeds per acre, which has increased from less than 12% of corn acres in 2007 to almost 30% of corn acres in 2013. The 36,000+ category is also gaining acres but at a slower rate of about 1% per year.
In the major corn producing states of Iowa, Illinois and Minnesota, the percent of acres planted over 33,000 seeds per acre is well over 50%, generally due to more productive soils, according to the survey.
In recent years, corn hybrid improvements in stress tolerance have led to higher populations and increased yield potential. However, as yields increase with each increment of higher seeding rate, a point is reached where the yield benefit from the next addition of seed no longer exceeds the cost of the seed. That point is the optimum economic seeding rate.
Finding the ideal plant population for your fields
A search for the ideal plant population led DuPont Pioneer researchers to focus on ears grown per acre to help corn growers achieve maximum yield. "The key components of yield are ears per acre, kernels per ear and kernel weight," says Scott Nelson, agronomy research manager for the seed company. "Of these factors, ears per acre have the most impact on total yields."
Genetic improvement of corn hybrids for superior stress tolerance has contributed to increased yields by allowing hybrids to be planted at higher plant populations. During high-stress growing seasons, corn plants still produce ears, although they may be somewhat smaller. In favorable weather, higher plant populations produce more ears and higher yields.
Even during less-than-ideal weather, today's hybrids maintain a more stable shedding-to-silking interval, which leads to better pollination of all the ears in the field.
Name of the game for increasing yields is more ears per acre
"While kernels per ear and kernel weight are important, the name of the game for increasing yields is more ears per acre," Nelson says. "We're working to help growers get consistent yields in stressful environments while maintaining the ability to achieve outstanding yields in ideal environments."
Every decision that you make influences the size and scope for corn yields. From the corn hybrid you select to the seeding rate and row width you choose. Download our FREE report over Maximizing Your Corn Yield.
"Growers should try to achieve the maximum number of ears per acre that their soil and growing environment allow," Nelson says. "The best way to do that is to make sure you have high enough plant populations to take advantage of favorable growing conditions."
Studies conducted by Pioneer across 165 environments in 17 states and three Canadian provinces resulted in a 4% to 8% difference in planting rate recommendations. The optimum planting rates ranged from 32,000 to 33,300 seeds per acre for hybrids with over 100-day Comparative Relative Maturity, or CRM. Earlier-maturing hybrids were most profitable at 34,700 seeds per acre.
"If you drop down to 30,000 seeds, you've limited your potential, in essence putting a ceiling on yields," Nelson says. "If the soil is fertile and the growing environment is favorable, higher plant populations offer the potential of the best yields — and the highest profits." Growers also should take care not to plant more seed than they need to avoid risks such as lodging.
Consider varying plant population based on field and hybrid
When weighing plant population options, growers may want to consider varying planting rates based on field and hybrid. While it seems logical to plant more seeds on the best soil, Nelson says there are exceptions.
"Some lower-yielding soils may need more seeds per acre to get enough leaf area to lift yields," he explains. "We know corn hybrids differ in their response to plant populations. Some may not respond to higher populations even on the best soils."
Pioneer continues research to find the optimal plant density levels for all hybrids under all environments, says Nelson. "The goal is to avoid overplanting or underplanting each field. Contact your Pioneer sales professional for planting rate suggestions specific to your farming operation."
Seeding rate recommendations: Challenging growing environments may reduce corn plant populations below optimum levels, notes Nelson. These conditions can occur when planting into no-till or high-residue seedbeds, or cloddy or compacted soils. Soilborne diseases and soil insects can also diminish stands. All these factors can interact to challenge stand establishment, and effects are magnified when planting early into cold, wet soils. Thus, he says you should consider the following points when choosing your seeding rate.
1) In general, plan to drop 5% more seeds than the target population to account for germination or seedling losses.
2) Boost target seeding rates by an additional 5% for extreme or challenging environments such as those described in the above paragraph.
3) In areas with perennial drought stress, seeding rate targets are lower. Base your seeding rate on the specific hybrid population response at the historical yield level of the field.