Corn plants demand perfectly uniform spacing within the row: old wives tale or agronomic fact?
The debate is older than the one about angels dancing on the head of a pin, and both debates are clearly lacking in scientifically sound evidence, says researcher David Clay.
Not understanding the disdain each individual corn plant has for its neighbours, novice growers often scoff at the idea that corn seeds must be evenly spaced down the row.
The result is random seed spacing and reduced yields because the air drill can’t handle singularization and a dedicated corn planter costs too much money.
Read Also
Agriculture ministers agree to AgriStability changes
federal government proposed several months ago to increase the compensation rate from 80 to 90 per cent and double the maximum payment from $3 million to $6 million
However, sloppy seed spacing also costs money.
“Uniform spacing is not just an old wives tale. It’s definitely an agronomic fact,” said Clay, a soil biogeochemistry researcher at South Dakota State University in Brookings.
Until recently, nobody had tried to figure out how or why corn plants know they need breathing space around them. There are a lot of assumptions, stories and theories that sound logical, but no scientific evidence.
Clay said everyone has always assumed it’s the shade factor because that’s what they were taught in high school biology, but nobody knew for sure.
“So we’re delving into the relationship between individual corn plants in an actual field setting, and we’re already starting to figure some things out.”
Clay said he may never solve the one about angels on the pin, but his initial research into corn indicates corn plants communicate with light.
Shooting down a long-held myth, he said shade is not the principle factor limiting the productivity of individual corn plants.
Farmers have always taken such good care of their corn crops that they may have created a weakling, a pampered crop that backs down from fights with weeds or other corn plants.
This withdrawal symptom might extend to the inability of modern corn to fight off disease, insects and other parasites.
“Corn has been domesticated for thousands of years. It’s lost the will to compete,” Clay said.
“So we’re thinking we need to go back and look at some of the things we’ve bred out of corn. Right now, our goal is to improve corn’s ability to compete with weeds.
“We already know that corn responds to its neighbours. A corn plant senses another corn plant nearby and thinks it’s a weed.”
At that point, the corn plant withdraws.
Clay’s initial research is aimed at identifying the signals a corn plant picks up on. How do they sense what’s around them to cause a change in their behaviour?
If that question can be answered, it steers researchers toward modifying corn’s cowardly behaviour.
“We think it has to do with the quality of light they receive,” Clay said.
“Not the quantity of light, that’s shade, but they can interpret the quality of light striking their leaves.”
He said that in early stages of growth, an individual corn plant already knows what’s around it long before shade from other plants becomes a factor.
A nearby plant of any kind will make the corn plant behave differently than if it’s surrounded only by soil.
“Leaves of the neighbouring plant absorb the red light waves in order to perform its own photosynthesis,” Clay said.
“The far red reflects toward the other plants. That’s how plants communicate. They read the far red light waves.”
The corn plant senses that a neighbouring plant has absorbed some of the red light it was waiting for. Even at its earliest growth stages, a young plant absorbs enough red that it can sense it.
In nature, that typically triggers the fight response, but the law of the jungle no longer applies to corn.
“We’re taught that, normally, a plant responds to other plants by competing. It tries to grow taller to get better access to sunlight. But corn doesn’t do that anymore. It backs down. Competition actually stunts the growth.”
Clay said he has run trials that have doubled the normal corn population, going as high as 60,000 plants per acre.
“If corn was a normal crop, you’d expect to go into that field and see tall rangy corn plants with no ears. That’s what your high school biology teacher would have told you. They should be fighting for sunlight.
“But instead, we go into that field and see short plants with good ears. It’s contrary to logic and contrary to what you’d see in nature.
“At the molecular level, a corn plant knows he has neighbours and he chooses to grow small. It down-regulates its own photosynthetic capacity so it fits into the overall community.”
If only a few plants do this, they die out and the general population competes for sunlight. But not in the corn community.
Clay said the cumulative affect of the whole field backing down is that it produces an environment in which each plant will still produce good ears and the overall field a good yield.
“We think it’s because we’ve bred corn to grow well in high, dense populations. This gives us better efficiency of water, nitrogen and all other inputs, but it requires more seed at a cost of something like $300 a bag.”
So the question for Clay is how to find that optimal point beyond which the financial return diminishes on each additional seed.
South Dakota corn growers typically aim for 30,000 to 32,000 plants per acre. At that point, they can hit 200 bushels on a good year.
Going up to 60,000 plants per acre still created an overall yield increase for the field, but the financial return diminished with each additional bag of seed.
“We had absolutely perfect growing conditions the year we seeded 60,000. We had all kinds of abundant growing degree days and it always rained just when we wanted it.
“That field averaged 230 bu., so it was just barely enough to cover the cost of the extra seed. And we may never see corn growing weather like that again.”
Clay said an ultra high seeding rate is not the way to increase profits on corn.
What will work is better weed control to get the corn plants off to a better start. It’s all a question of when to spray for weeds.
Clay said a young corn plant is able to detect the presence of alien neighbours as early as the two-leaf stage.
At that point, it already starts to respond by down-regulating its young photosynthetic system, even with an abundance of moisture, sunlight and nutrients.
“The mere presence of any other living plant material causes the young corn plant to back down. That’s why we need to spray for weeds between the two leaf and six leaf stage.
“We want those weeds dead, not just because they consume moisture and nutrients, but they send negative signals to the young corn plants.”
Clay said that also explains the need for perfect plant spacing within the row. If two corn plants wind up close to each other, they inhibit each other’s growth potential just as dramatically as a weed.
If every corn plant in the field is an equal distance from its neighbours, the entire population will optimize the yield potential of the whole field.
Clay said he has started parallel research on light sensitive communications in soybeans and wheat.
