Soil temperature is the final indicator Randy Dowdy watches as he pulls the trigger on another planting season.
"Before I plant, the (soil) temperature has to be 56 degrees (Fahrenheit)," Dowdy said. "Or there has to be a strong warming trend for the next week." Quick emergence is key. Dowdy wants to see his corn crop emerge within 10 days or less after planting. "Preferably within seven to eight days to get maximum yields," he added.
Dowdy farms outside Valdosta, Georgia, and was the 2014 world corn-yield record holder. His 503.7910-bushel-per-acre yield in 2014 topped all others in the 50-year history of the National Corn Growers Association (NCGA) National Corn Yield Contest. The yield was pulled from an irrigated, twin-row field.
Last week, Dowdy's record was beaten by David Hula of Charles City, Virginia, who set another world-record corn yield with 532.0271 bushels per acre in his entry into the 2015 NCGA corn yield contest.
Dowdy farms 1,700 acres -- 470 acres of corn, 300 acres of peanuts and 200 acres of double-crop wheat and soybeans. His management practices are reported on his website, www.growbigcorn.com.
Corn progresses through its growth stages according to accumulated heat. Heat accumulation is expressed in growing degree units (GDU) or as growing degree days (GDD). The terms are interchangeable.
As the temperature rises above 50 degrees Fahrenheit, and assuming adequate moisture, the germination process unfolds as GDUs accumulate. By Dowdy's calculation, 56 degrees means the soil is warm enough for his corn seed to absorb, or imbibe, 30% of its weight in water for the radicle root to emerge, followed by the lateral seminal roots. Within the first few days, the first true leaf forms.
Dowdy looks for his first spikes within 75 to 110 GDUs, depending on seed depth and the vigor of the hybrid. From beginning to end, he wants to see his entire crop emerge within 10 GDUs of one another.
He believes strongly that uneven emergence -- and by uneven, he means emergence spread out over too many hours, certainly not days -- is the enemy of yield. If his hybrids have a theoretical potential of 600 bushels to the acre, uneven emergence is going to be one of the first serious subtractions from that number.
His high-yield formula is straightforward: Plant stress equals yield lost. "You either eliminate stress, or you address it," Dowdy said.
Uneven emergence is one big stressor -- but one that the grower has some ability to manage, he said.
Dowdy has learned a great deal from his on-farm field trials. But one lesson stands out from all the rest. "When you see a plant come up 24 hours later than the others," he said, "you now have a weed with 25% less grain on it." Actually, according to calculations from one test, the 25% of plants that emerged 12 hours after the first had 23.8% fewer kernels on their ears.
Dowdy weighed the difference, too. The weight of an ear on a plant emerging 24 hours after the first corn spike emerged is two-tenths of a pound lighter. It is a small amount of weight that, when replicated over an entire acre, represents a significant amount of lost production.
"That difference just cost you a bunch of money," he said. "If you want a 300-bushel harvest, you need a 300-bushel stand."
Some will argue whether late-emerging plants are doomed to life as mere weeds. But there is broad agreement that even emergence is crucial to final yield. According to an agronomy research paper published by DuPont Pioneer, uneven emergence (measured by plant development or by percentage of emergence, among other measures) can lead to a yield loss of 5% to 9%.
(For the full research paper, go to Planting Outcome Effects on Corn Yield at http://bit.ly/…)
Dowdy has a simple way to prove the travails of uneven emergence. It is with small survey flags. Here's what he does with them.
Just before the corn emerges, he walks off a 20-foot row section in a field. As the first plants spike, he puts a colored flag beside every one of them. He returns in 12 hours and places a different colored flag by every newly emerged plant. Dowdy repeats the process every 12 hours with different colored flags until all the plants in the row section have emerged. At the end of the season, he separates the ears from that row section according to the colored flags. He weighs the ears and counts the kernels.
There will be a telling result, he said. "This will be your 'ah-ha' moment. You will understand the cost of variability and lost yield from Day 1," Dowdy said.
Hand in hand with good emergence is planting depth, Dowdy believes. "I'm going to plant at 2 inches, not two-and-a-quarter or one-and-three-quarters. I want to get that seed into the ground at 2 inches." That is a depth far enough into the soil to protect the seed from early-season variations in temperature. It also is a depth where soil moisture levels are more stable. Any shallower, and that seedbed is vulnerable to weather that suddenly turns dry or too wet.
Center pivots give Dowdy good control over his early-season water needs. If the soil is too dry, Dowdy will turn them on. If crusting develops from too much rain, Dowdy will turn on his center pivots to break up that crust.
WATER CORN UP
He has no hesitation to water his corn crop up out of the ground, he explained. To boost his opportunity for even emergence, Dowdy routinely applies two- or three-tenths of an inch of water with his pivots just as his corn crop is ready to emerge.
Dowdy can point to a clear example of the need for water right at the moment of emergence. His record yield came from a tough-to-farm soil with a fondness for clods. In the past, he has planted 52,000 seeds to the acre in it, only to see 32,000 plants emerge. He has worked to increase the soil's organic content with late-planted peas and cover crops to make the soil more conducive to high-yield corn. But in 2014, a 4-inch rain broke down the clods just before emergence, and 52,000 plants emerged. Several months later he recorded a 500-plus-bushel world record.
There's nothing particularly earthshattering about Dowdy's recipe for big yields. It is the details that count. He is a close observer of his crop, and he does everything he can to remove stress from it. Dowdy walks his fields every day. And he is an adherent to Liebig's Law of the Minimum. The Law of the Minimum states that crop growth is controlled not by the total amount of nutrients available, but by the scarcest nutrient available to the plant.
In his take on the Law of the Minimum, Dowdy also considers plant population, skips and doubles, compaction, weed control, insect damage, plant disease, too much or too little water, poor drainage, planting errors and harvest-time losses.
"The best thing I can see in my corn field is my shadow. It means I'm out there observing what the plants tell me they need. If you're in the field with your eyes open, you can find all of those minimums. You've just got to look and care about doing what you can to relieve plant stress," said Dowdy.
Editor's note: From its very first day, the corn seedling is under attack by much of the world around it. Weeds are its biggest threat, stealing yield from the moment the corn seed settles into the bottom of the seed trench. In this series, DTN/The Progressive Farmer looks at why weed control and good early season practices are key to producing high-yielding corn crops. This is the second of a six-part series.
© Copyright 2015 DTN/The Progressive Farmer. All rights reserved.