For years there has been a focus on achieving the perfect “picket fence” spacing in corn fields. As a little girl, I was taught that you could just about find a corn seed in the distance from your thumb to your middle finger down the row. Years of research has shown that when corn plants are not spaced perfectly, yield potentially lowers. Plants that are too close to one another start to compete for sunlight, water, and nutrients, and one plant will end up dominating while the other will become the “weed.”
So, why wouldn’t the same be true for soybeans? The soybean plant is a different kind of animal and has a great ability to compensate for uneven stands, unlike the corn plant. Maybe you have some plants that emerge late due to cooler soil temperatures. Maybe you lose some plants very close together. Maybe you lose some plants from deer damage or have two plants very close together. The thought has always been that soybeans will compensate, so it doesn’t matter. The plants around the lost or delayed plants will start to branch out and fill in the gaps in spacing, and by mid-season, the field looks like it has recovered.
Over the last couple of yeas, universities and industry professionals alike, have started recommending lower soybean plant populations due to this branching effect. Seven-year, multi-location data from the University of Illinois shows that the Economic Optimum Seeding Rate (EOSR) for 15-inch rows is 100,000 plants/A. and 15-year PFR data shows the same. If you pay attention to the national soybean yield contest, the yield winners have been lowering their plant populations and have started to focus on spacing and its potential to add more branches to the plant. Theoretically, more branches means more nodes, more nodes means more flowers, and we know that more flowers means the potential for more pods, if we can keep them from aborting.
When giving PFR tours this past summer, one of the studies we were most excited about was the soybean singulation study. Precision Planting sent us 56-cell singulated plates to be put to the test, and the visual observations were present throughout the growing season. We tested these plats at 100,000, 140,000, and 180,000 plants/A. Visually, the lower populations had more branching and the highest population didn’t show much visually. The plants were too close together to do much branching, even when singulated.
It is important to remember that these extremely low populations are successful when planted early and when the planter is well-tuned to achieve singulation. We do not recommend that farmers dramatically decrease their soybean populations overnight, but we do encourage you to put extra effort into your soybean planter, and to work toward a picket fence stand. Our PFR findings, together with Becks’s Escalate® seed treatment, justify putting in a few test strips where you may lower population by 10 to 15% on your early planted soybeans.
As we continue to increase our bushels per acre, this may be one piece to figuring out the high-yielding puzzle. Check out our PFR data in the 2019 PFR Book, and participate in a PFR tour this summer to see the branching effect for yourself.
~Camille Lambert- Field Agronomist