Soybean School: Should you plant soys before corn?

OMAFRA soybean specialist Horst Bohner

Traditionally, when the soil is fit for planting, growers fill the planter with corn seed and start to roll.

But is it time to rethink that time-honoured approach? Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) soybean specialist Horst Bohner believes so. He says there’s plenty of evidence to suggest early-planted soybeans deliver a yield boost comparable to early-planted corn.

On this edition of RealAgriculture’s Soybean School, Bohner explains why early-seeded soybeans can deliver up to a 10-bushel yield advantage in Ontario. One of the main factors is that early-planted soybeans harvest more sunlight. With early planting comes faster canopy closure and less sunlight is wasted in the first half of the growing season.

Bohner notes that soybeans are also extremely daylight sensitive. When the crop is planted early, plant growth stages that are key to higher yields take place during longer summer days with more sunlight. He adds that early seeding allows plants to produce more nodes, which leads to more pods per plant and higher yield.

In the video, Bohner discusses a 2018 research trial at Winchester, Ontario, that studied soybean yield when the crop was planted at three different times — May 10, May 30 and June 21. He explains that the trial showed a 5 bu/ac yield advantage for May 10 over May 30 and a 15 bu/ac advantage for May 10 over June 21. He notes that poor spring conditions delayed trial planting and expects the same yield differences would be seen if the planting timeline was two weeks earlier. Story continues after video.

Variety selection is critical to cashing in on early planting. Bohner notes that growers need to plant longer-season varieties if they want to see the full potential of earlier planting in the grain bin. In his Winchester trial, all varieties — both short and longer season — yielded essentially the same when seeding was delayed. But, the longer-maturing varieties did yield more at the first planting date. Check out Field Crop News for more of Bohner’s research insights.

So what does Bohner tell growers who ask if they should plant soybeans before corn? Since both crops suffer large yield reductions from late planting, the best answer might be to suggest that both crops should be planted at essentially the same time, especially in southwestern Ontario, says Bohner. If soil, temperature, and moisture conditions are suitable for planting corn they are also generally suitable for planting soybeans.

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