Corn School: How much rain does corn need?


Weather is the ultimate source for small talk, and rainfall is perhaps the most talked about — from how much, to when, to not enough, and on too much.

For this episode of the Corn School, Bernard Tobin asks Dale Cowan, senior agronomist at AGRIS C0-operative, about how much rain a corn crop needs throughout the season and about the critical times during a crop’s growth that it needs that rain. Plus, once we have that knowledge, how do we manage our soils and crops to make sure we have moisture throughout the season?

“At this growth stage (six to seven leaf), roughly it’s been at least four inches of rain, maybe even closer to five,” says Cowan. “That’s a combination of not just rain but also stored soil moisture as well.”

A high yielding corn crop could consume approximately 25 inches of moisture per acre, per year, says Cowan, which is a substantial amount. By the tassel stage, the plant will have consumed about 10 inches of water, and the remaining 15 inches will be needed during the reproductive stage.

“It always amazes me that even at dent, just prior to black-layer, we’re still looking at 0.18 to 0.2 inches of water per acre per day, even though we’re almost finished the crop at that time, so water use goes right up to black-layer,” says Cowan.

For optimal yield, a corn crop needs pretty steady moisture throughout germination and emergence and  into the vegetative stage, but the most critical point for the crop to get moisture is at tasselling or silking stage — almost 10 inches of water is required between the R1 and R5 growth stages (Story continues below video)

Digging a bit deeper into management strategies for retaining soil moisture, Cowan says that means starting to look at more complex rotations, including cover crops, less tillage, more residue left on the soil surface which reduces the evaporation rate and increases water infiltration rates, and adds more organic matter to the soil — every one per cent of organic matter, holds one inch of water, says Cowan.

“Those are the things you start to see make a difference, especially when it’s dry  or somewhere where we have a moisture deficit,” says Cowan.

If leaf-roll occurs before the reproductive stage, as long as it doesn’t exceed 12 hours per day, Cowan says it won’t have a huge impact on yield.

“I think that yield loss is very much dependent on what’s causing the leaf rolling,” says Cowan. Soil management, fertility, and moisture all get layered and can make that little bit of difference throughout the growing season.

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Corn School (view all)Season 10 (2021) Episode 19

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