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Zero In On Population

October 23, 2013
By: Rhonda Brooks, Farm Journal Seeds & Production Editor
photo
Improvements in seed corn genetics have resulted in hybrids that perform best when planted in higher populations, according to George Holsapple, center, who farms with his wife, Janice, and son, Thad, in central Illinois.  
 
 

Identify hybrids that thrive at higher seeding rates

Row after row of short-statured corn stretches across George Holsapple’s central Illinois farm near Jewett. But he is neither disgruntled nor even mildly disappointed with the crop’s under­whelming size. Rather, he is focused on its performance, and he is pleased with what he sees.

"This is a fine-looking hybrid; the ears are 14 to 18 rows around and 40 to 45 kernels long," Holsapple says happily. "It’s not a tall hybrid, but high-population hybrids tend to be short."

Small stature aside, he believes the hybrid has the necessary genetics to help him break through his current yield plateau. His goal is to reach a higher average yield and, perhaps, even the 300 bu.-per-acre average the seed industry sees as the future gold standard for the central Corn Belt.

Data from the past 80-plus years illustrate that as farmers have bumped up corn planting populations, yields have increased as well. Research by DuPont Pioneer shows that the average corn seeding rates used by farmers in the U.S. and Canada have increased from about 23,000 seeds per acre in 1985 to nearly 31,000 seeds in 2012, an increase of about 300 seeds per acre each year. During that same time period, U.S. yields increased from an average of 105 bu. to nearly 160 bu. per acre—about 2 bu. per acre per year. Today, about 35% of North American corn acres are planted at 33,000 seeds per acre or more.

Genetics are the cornerstone. Hybrids suited to high populations tend to have some similar genetic characteristics, says Mark Jeschke, DuPont Pioneer agronomy research manager. He says such corn hybrids are designed to root deeply and stay greener longer during the growing season than their counterparts. Their leaves tend to be narrow and grow straight up, not outward. This upright structure helps accommodate higher plant densities and allows sunlight to penetrate down into the ear leaf to maximize photosynthesis.

Also, as Holsapple reports, these hybrids also tend to have a compact plant structure, though not all do.

Perhaps the most important single characteristic high-population hybrids share is that they thrive under the stress of being packed tightly in a corn field like canned sardines.

It’s the condition under which they perform best, says Myron Stine, vice president of sales for Stine Seed. This year, the company planted all of its corn hybrids in 12" rows and at various plant populations, ranging from a low of 45,000, a mid-range of 55,000 and a high of 65,000.

"What we’re doing isn’t about 12" rows, though that’s what grabs everyone’s attention," Stine emphasizes. "It’s about developing better genetics that can handle higher populations."

The use of narrow rows is a hot topic today for farmers looking to break yield boundaries. Just this season, with the help of Stine district sales manager Brad Ramp, Holsapple went to 15" rows for his entire corn crop. Part of the transition included putting in place an extensive management system and fine-tuning his planter, which uses the Precision Planting system for variable-rate seeding and fertilizer. Holsapple manages his nutrient program with soil and tissue sampling via the Conklin AgroVantage System.

"Tissue sampling prior to V3 lets me see what micronutrients are missing," Holsapple says. "I can then spoon feed the plants with foliar feeding to keep them healthy and the roots actively looking for more nutrients."

Stine says not every farmer is ready to use narrow rows or has the soil and environmental conditions to benefit from them. He does believe most farmers can select corn genetics that allow them to boost their populations and thereby improve overall yields.

Jeschke agrees: "Our central Corn Belt research and some university studies show that to maximize corn yields, you need 95% light interception or above at silking. You can accomplish that through most of the Corn Belt with 30" rows."

Bob Nielsen, Purdue University Extension agronomist, cautions farmers on pushing their seeding populations in a vacuum: "The optimum final plant population is that which best balances the benefit of more ears per acre with the disadvantage of smaller ears and lighter grain.
Furthermore, stalk health and integrity often falter as plant population increases beyond some maximum threshold."

Joe Lauer, University of Wisconsin Extension agronomist, offers a corn ear weight-assessment tool for farmers to try this harvest, and they can use the results to help make plant population decisions for next spring.

"A corn ear weight of about 1⁄2 lb. is what you want to achieve. If the average ear is greater than 1⁄2 lb., then the population was too low," Lauer says. "If the average ear is less than 1⁄2 lb., then the population was too high.

Another indicator of too high a population is an abnormal number of barren plants. Fields planted at too high a population have a higher degree of lodging, poorly filled ear tips and a greater number of barren plants."

Holsapple planted his high-population hybrid at rates that varied up to 48,000 plants per acre. One significant benefit of variable-rate seeding is that it kept his 2013 seed costs at 2012 levels. What he learns this fall will guide his decisions in 2014.

Farmers interested in experimenting with high populations and narrow rows can get a portion of their 2014 seed corn for free from Stine Seed. To qualify, they must be willing to plant the company-selected hybrid at populations higher than 38,001 seeds per acre and in 20" rows or less. In return, farmers are asked to share their results with the company. 

Identify the Ideal

There is no simple formula for planting higher corn populations, according to Joe Lauer, University of Wisconsin Extension agronomist. He tells farmers that the ideal plant population in their fields depends on several factors, including:

Soil type. Heavier, finer-textured soils have better water-holding capacity and can support higher populations than lighter, coarse-textured soils.

Planting date. As you increase plant populations, an earlier planting date becomes a more important consideration for maximum performance.

Hybrid selection. Some hybrids tolerate high populations better than others. Maturity is important. Shorter, earlier hybrids are usually more responsive to high populations than tall, later hybrids.

Soil fertility. To support yield increases, Lauer says high populations tend to need a higher level of soil fertility, particularly phosphorus and potassium.

Moisture availability. Plenty of moisture is needed for higher populations, although some newer genetics perform well with average moisture.

You can e-mail Rhonda Brooks at rbrooks@farmjournal.com.

seeding pop

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FEATURED IN: Farm Journal - November 2013
RELATED TOPICS: Agronomy, Precision, Production, Seed

 
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