Fiddling with soybean seed depth brings risks

Experts say you’re supposed to plant soybeans one inch deep, give or take a quarter of an inch.

But many producers are going deeper when searching for moisture in dry periods, or shallower when the soil is moist and they’re keen to get the crop off to a quick start.

More and more growers — especially in atypical planting years like this one — seem to be fiddling with planting depth, pulse crop specialist Dennis Lange said at the Manitoba Crop Diagnostic School last week.

“Planting them deeper also exposes them to colder soils, and there’s always the question of how quickly they’ll emerge,” said the specialist with Manitoba Agriculture, Food and Rural Initiatives.

“Planting at half an inch can work if you get the rain — but you could be in trouble from just the slightest change in the forecast.”

To put this theory to the test at the CDS, organizers planted soybeans in five different treatments: three inches deep, two inches deep, one inch deep, and a half an inch with and without simulated rainfall.

The deeper treatments saw delayed emergence, especially at the three-inch depth, which Lange said would likely have a measurable impact on yield at harvest because of the physiology of the plants and their reaction to sunlight.

“At the end of the day, soybeans depend on the length of daylight to start flowering,” Lange said. “If that happens when the plants are still small, you’re going to have lower yield potential.”

Generally the results were as expected. The shallowest treatment germinated with rain, but struggled under dry conditions. The deeper two treatments were somewhat delayed, but the one planted at two inches was better than three inches, emerging more quickly.

“It basically boils down to three choices in the spring — plant at the optimal three-quarter inch to 1-1/4 inch, plant at a half inch, or plant at two inches,” said Lange. “The three-inch planting isn’t viable at all. If you do decide to plant either shallower or deeper, understand that you’re taking a calculated risk and it might not work out for you.”

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Gord Gilmour

Gord Gilmour is Editor of the Manitoba Co-operator.

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