Don’t plant soybeans at the end of April – here’s why

Written by Kevin Toews on Feb 10 2017

Category: Grow Grain

Don’t rush to plant soybeans this spring. Waiting for the right soil temperature will pay off with faster crop emergence.

Soybean acres are on the rise in Manitoba and Saskatchewan. It’s great to see so many growers adding this profitable crop to their rotations. But before we can get those big yields at the end of the season, we need to get the best possible plant stand at the start. Even if you have a lot of acres to get through, don’t rush to plant soybeans this spring. Waiting for the right temperature will pay off with faster emergence. Here’s why.

Soybeans’ growth point can’t tolerate frost

An illustration showing the difference between epigeal and hypogeal germination in crops.

Source: Begoon (This file was derived from Germination.svg) CC BY-SA 3.0, via Wikimedia Commons

Soybeans and canola have an epigeal growth point. That means once the plant has germinated and emerged from the soil, it continues growing from a point above the ground. Crops with epigeal growth points are susceptible to frost damage. If we get a full moon with clear skies in early May, the frost can be hard enough to kill any emerged soybeans. Soybeans can survive a frost down to minus -2°C if they have been acclimatized a few days in advance of the frost.

Wait to plant soybeans between May 10 and 25. Historically, that’s when your chances of a killing frost decreases in Manitoba, and the soil has reached the ideal temperature for beans. Warm soil means warm groundwater and that’s what soybeans like. Soybeans in the first 24 hours will take in a great deal of water and the warmer the water is the higher your seed survival rate will be.

For faster emergence, wait for 10°C+ soil

University of Manitoba agronomy Professor Yvonne Lawley and graduate student Cassandra Tkachuk recently published a study on the relationship between soybean planting dates and soil temperature. They found that cool temperatures delayed soybean emergence and warm soil temperatures resulted in rapid emergence.

In Manitoba, there are not many years where April’s soil temperature climbs above 5°C. If you seed into soil that’s between 5 and 10°C, your soybeans will take 14 to 21 days to emerge – not exactly the head start you had in mind. Plus, soybeans do not like cold ground water. It stresses the seedlings, making them more vulnerable to damage from disease and insects.

Lawley and Tkachuk’s study found 14°C was the ideal soil temperature for fast soybean emergence. In my experience, you can safely plant soybeans when the soil has been at least 10°C for two days in a row. Then they pop out of the ground in 10 to 14 days.

Plant your cereal or canola fields first

It's now common practice for growers to drop everything they are doing when it's time to seed soybeans (when the soil is warm, the groundwater is warm and the calendar date is right). They prioritize planting soybeans so they can maximize the crop's yield potential.

Cereal crops like wheat, barley, oats, rye and corn have a hypogeal growth point, which means they grow from a point below the ground. A heavy frost will kill the leaves, but the plant will continue growing from below the soil surface. Soon, you’ll see new leaves.

Even though canola has an above-ground growth point, it’s tough enough to tolerate soil and ground water that’s a little cooler than soybeans.  

Planting date is just one area where soybeans require a little different care than the crops we normally see in Manitoba. If you’re growing soybeans for the first time, talk to your Cargill representative. We can share advice to help you make the best agronomic decisions for your soybeans. It’s an easy way to set up a successful year!

Tags: Soybeans, seeding, agronomic advice, Crop Establishment

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