Blooming Before Solstice

This Week In Ag #171

“Knee-high by the fourth of July” is one of the most popular – and outdated – sayings in farming. It likely originated before the adoption of hybrid seed corn, a century ago. Corn is already over head-high in many parts of the country.

But what about soybeans? Do they have an outdated saying? Actually, you might say they have a recently outdated saying.

Soybeans are a short-day plant. They react to night length to determine when they transition from the vegetative to the reproductive phase of their life. As of today, night lengths are starting to get longer. That’s because Sunday marked the summer solstice, the longest day of the year in the northern hemisphere. From now until December, days will become shorter.

This reduced photoperiod is Mother Nature’s way of triggering plants from the vegetative to the reproductive growth phase.

“Soybeans don’t flower until after the summer solstice” was a long-held belief. But if you walked through soybeans last week, you could have found flowers in some fields. How is that? Isn’t it not nice to fool Mother Nature?

Early planting dates have changed the dynamic for soybeans. Shifting planting from May to April (and even March in some cases), combined with spells of warm weather, speeds growth through the vegetative stages and enables the plants to set blooms earlier – even before the summer solstice.

Soybeans are highly responsive to light, so the more sunlight you can give them, the better they should perform. Planting soybeans early is all about getting ahead of the summer solstice, lengthening the vegetative growth period, and producing more branches, nodes, blooms and pods. By closing the crop canopy sooner, you can maximize the prime sunlight of the summer solstice.

The results don’t lie. An 8-year study by Precision Planting in Illinois showed soybeans planted in the first half of April outyielded those planted in the first half of May by 20 bushels per acre. A two-year study by Mississippi State showed that April-planted soybeans outyielded May-planted soybeans by 10 bushels. These days, many farmers are planting soybeans first, ahead of even corn. It’s now common for Midwest farmers to use two planters, equipping one for corn, one for soybeans.

While soybean growers harvest oil seeds, soybean plants themselves harvest light. The more leaf area you spread across your field, and the faster you do it, the more efficient plants are at utilizing sunlight.