It’s no secret that corn loves sunshine, but a University of Guelph scientist was recently surprised to discover that corn can see the colour of that light and use that ability to tell if other plants are nearby.
Clarence Swanton stumbled across this phenomenon while researching corn’s reaction to early-season weed control.
“We knew that corn reacted very positively to early season weed control – up to 20 percent improvements,” he said.
“We just didn’t know why.”
Moisture is usually plentiful enough early in the growing season to support corn seedlings and weeds.
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Because the plants are small, they all get enough sunlight. But there lies the mystery. If the tiny weeds aren’t stressing the corn seedlings, why does weed removal at this time of year result in such dramatic yield improvements?
It appears that corn changes its carbon allocation according to the type of reflected light it receives from the ground and its surroundings.
The colour of light reflected off weeds is different from light reflected off bare soil or other corn plants. It appears corn has a physical mechanism to measure light’s colour temperature and adjust its behaviour accordingly.
When it senses there are more non-corn plants in its vicinity, the corn plant puts additional resources into its stalk and leaf development, growing taller and fuller more quickly. But this early growth spurt doesn’t translate into bigger yields at harvest.
To grow tall and choke out competing plants, corn sacrifices its root development that would otherwise provide additional nutrients and water throughout the growing season.
“It has been known forever that corn doesn’t compete well in the early stages, but the reasons were never well explained,” Swanton said.
Also unexplained was why corn fails to thrive in reduced and no-till applications. It turns out the additional surface litter may change the reflected light’s colour temperature at the far red end of the spectrum.
“This isn’t about the corn plant being sha-ded, it is about the plant’s ability to perceive and detect other plants around it and reacting accordingly.”
Swanton said his research proves the need for early-season, in-crop weed control.
“Thinking that you can wait to do weed control, no matter how effective it is (at a later stage), could be a big mistake in corn crops.”
In trials last season, Swanton and his research team simulated weedy and non-weedy early crop conditions.
By the four-leaf stage, corn in the weedy plots was 17 percent taller, had 45 percent more leaf area and 40 percent more leaf matter.
The still-young plants had determined where to place their resources for the entire season.
The young plants that sensed competition also had a 12 percent higher shoot-to-root ratio, meaning there would be fewer roots to gather the nutrients and moisture needed for yield and growth later in the season.
In non-weedy situations, corn plants spread their leaves wider, closing in the canopy faster and more fully than the weed-affected plants that send their leaves up, parallel to the stalks.
Swanton said early-season weed control gives plants the chance to close in the canopy more rapidly and take care of later-season weeds by choking off their supply of light.
“That means helping to avoid later season weed control using costly herbicides.”
Swanton said beyond the additional $20 to $40 per acre in improved yield, there are less definable long-term benefits such as fewer weeds maturing and adding to the soil’s seed bank and reducing later-season water and nutrient resources.
The next step is to find out if other cereal crops act in the same manner.
Swanton has just begun such a study, using popular western Canadian barley varieties.
“It would be very interesting to see how other cereals see,” he said.
