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The challenge of even crop emergence

It’s a frequent subject but it’s also a source of conflict for many corn growers

In the days before the COVID-19 pandemic, talk during winter meetings and even well into spring centred on three key discussion points with corn: plant when the ground is fit, plant to moisture and pay attention to the critical weed-free period. Each comes under the heading of “giving your corn crop the best start,” because the stronger your start, the better you’ll be able to make use of the entire season.

There’s another goal too, of course. It’s to do all you can to encourage even or uniform emergence. But sometimes, it’s the hardest to achieve.

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It isn’t that growers aren’t trying, says Paul Hermans, a territory manager and certified crop advisor (CCA) with Pioneer Brand Products (part of Corteva Agriscience). Instead, it’s down to the vast number of stresses and variables that go into a growing season.

Hermans oversees a wealth of plot tests and demonstrations across Eastern Ontario, enhancing that with information and research from the U.S. He echoes a sentiment often shared about seed — that its greatest potential is while it’s still in the bag — and he knows an increasing number of growers use that phrase as a kind of slogan, and an incentive for continuous improvement.

A wealth of research

Different scientists have impressed upon growers the need for getting corn off to the best start possible. Dr. Clarence Swanton from the University of Guelph provided his initial findings on the critical weed-free period more than 20 years ago and has updated the standard since. Dr. Fred Below from the University of Illinois has his “Seven Wonders of the Corn Yield World.” They include weather, nitrogen, hybrid (selection), previous crop, plant populations, tillage and growth regulators.

But confusion creeps into other bits of advice, including prioritizing planting in a rushed season. Is it best to interrupt corn planting to get soybeans in the ground — since that crop’s growing season is shorter — and then go back when the beans are done to finish the corn? Or is it better to stay the course on corn and get that whole crop before moving to soybeans?

The hybrids of today are capable of withstanding stresses of higher populations.
photo: Supplied

There are a lot of questions concerning “the best start” and although Hermans agrees that uniform emergence is an important goal in boosting a corn crop’s potential, he cites planting depth and populations as two key criteria. The optimum time frame for emergence, he notes, is 24 to 48 hours, yet there are many factors — like soil type, soil moisture and temperatures — that are beyond a grower’s control. It means the exact time of emergence is controllable, but only to a point. Instead Hermans echoes the real estate phrase “location, location, location,” except with corn, it’s “planting depth, planting depth, planting depth.”

“We have to have the best planting depth and maybe go a little deeper than we’re used to in order to get this uniform emergence,” says Hermans, who is based near Richmond, a half hour southwest of Ottawa. “If you take one of 1,000 plants or one in 17-1/2 feet, that’s seven to 10 bush- els. That’s where you get into this component of even emergence, and how can we make that consistent going forward?”

He refers to plots he ran on depth-of- planting within a few miles of each other. Both were planted to depths of 1.5, 2.0, 2.5 and 3.0 inches and underwent daily counts (see Table 1 below). Location 1 was planted May 15 at a population of 35,000 seeds per acre. Temperatures on May 15 and 16 averaged 20 C for the high and 6 C to 7 C for the low. Location 2 was planted May 28, with 34,500 seeds per acre and temperatures for May 28 and 29 averaged 22 C as the high and 10 C to 14 C for the low temperatures.

“Deeper was better in terms of more uniform emergence later, and that showed in the daily counts,” says Hermans. “If I’m a customer who’s trying to get the crop out of the ground and uniform, I would rather do the 2.0- to 2.5-inch range going forward. What I find is that you’re going to be a day or two later emerging but in most cases, it will be uniform if you went an inch-and-three-quarters to two-and-a-quarter.”

Graphic: Supplied

Further study

Another research project with Pioneer in 2015 found that planting depth is a primary factor in ear weight and length as well as uniform emergence timing.

There is less temperature and moisture variability deeper in the profile, which possibly allows for more uniform germination, the research summary says.

A three-year study at Ohio State University from 2017 to 2019 that assessed the impact of soil temperature and moisture flux on emergence in corn planted with varying soil classes and characteristics confirms this. Its key findings

included that shallow planting shortened the time to the start of corn emergence yet prolonged the time frame of emergence, resulting in a stand that was less uniform. The study also determined that soil moisture was lower and more variable at shallower depths, potentially con- tributing to less-uniform emergence with shallower planting. Finally, planting depth affected yield in soils with higher soil organic matter levels but had no impact on a field with lower SOM levels.

“The biggest thing is that, as a grower, we think of going into a field with the intention of planting at two inches but it could be a quarter-inch either side of that target,” says Hermans. He tends to favour the deeper depths to ensure a better chance of planting to moisture. “Above all, the corn seed does not like extremes.”

Other influences

Many of the standards that are recommended in row-crop production are presented as ideals: 24 to 48 hours for emergence, managing weeds at the earliest point after emergence, optimum planting depths and populations. But there are lots of realities affecting planting, herbicide applications, the use of fungicides. One is the size of a farming operation and whether that can cause some logistical headaches at planting. Having fields at different locations — a trend that’s on the rise — can challenge a grower in the best of planting seasons. Plus, is the field relatively flat, or are there hills or knolls to contend with?

Planting depth leads to uniform emergence and consistency across a field.
photo: Supplied

Another factor that’s gaining recognition with respect to even emergence is the variability of soils across a field. It’s easy to tell growers about the advantages of uniform emergence but with larger fields and greater variability, Hermans is less concerned with getting plants up at the same time if one end of a field is sand and the other is clay. It’s better, he says, if there’s consistency within those soil zones.

“We saw a lot of this in 2020 where with every eight plants, you have one or two that don’t produce,” adds Hermans. “That will hurt you a lot. But if it’s consistent and one side is a leaf behind and the other is a leaf ahead, as long as it’s consistent within a crop zone or soil zone, I’m not as worried.”

Planters are better

Calibration and planting speed are also mentioned for their potential impact in a corn crop’s performance, yet Hermans doesn’t believe calibration is as much of a problem today as it was years ago. Today’s equipment, he says, is simply more sophisticated and can handle different soil types and conditions. The same is true with planting speeds as more growers adopt high-speed models for their operations.

“But I’ll caveat that by saying it’s a con- cern if you’re going with speed through rocks and with lots of sod that can affect that seed depth,” counters Hermans. “It’s also dealing with the residue and how we manage that.”

As an example, eastern Ontario growers had to contend with weakened soybean stands during the 2020 planting season, resulting from a late corn harvest and high residue levels in 2019. That caused planter bounces and the inability for the planter or drill to cut through the residue. For the most part, however, Hermans believes larger growers — often with newer equipment — are managing this issue better now than in the past.

Tip of the hat

It also helps that corn hybrids are simply better at withstanding many of the stresses that arise during a growing season, which is thanks in part to plant breeders, who have steadily improved on the genetics. One study (see ‘Pioneer Era Studies’ graphic above) conducted by the late Dr. D.N. Duvick in 2005 compared hybrids from different eras — the 1930s, 1950s, 1970s and the 1990s. The results found the yield potential and ability to plant higher populations increased as the years passed. In effect, a hybrid from the 1990s not only out-yielded its 1930s cousin but plant populations on the 1990s hybrids were considerably higher (from 18,000 per acre in the 1930s to 29,000 with those from the 1990s).

“The hybrids of today can take more stress,” says Hermans, adding that much of corn crop’s performance relies on consistency. “And when we talk about stress, it’s about putting a plant from seven inches to six or even 5.8 inches between plants.”

This article was originally published in the January 2021 issue of the Corn Guide.

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