If you haven’t purchased soybean seed for next year yet, you will soon. How much of next year’s yield potential relies on genetics, and how much is tied to your management ability? Shaun Casteel believes it’s a 50-50 split.
“About half of the yield traces back to genetics, and about half depends upon your management of the crop,” says the Purdue University Extension soybean specialist. Management includes things like weed control, soil fertility, insect and disease control, and target planting date. It also includes selecting a seeding rate that will give you an effective stand.
Here are Casteel’s thoughts on target soybean population and resulting seeding rate, from an interview he did with Indiana Prairie Farmer.
Do many farmers still plant more seed per acre than they need to? Based on our trials, I believe that they plant more than necessary in many cases. For example, if you’re in 15-inch rows using a split-row planter which has good seed depth control, our recommendation would be about 100,000 to 120,000 seeds per acre. That should give you about 100,000 plants per acre, which is more than enough to deliver full yield potential.
How low can you go on plant stand and still harvest full yield potential? That likely varies by location. We have an unusual situation in southeastern Indiana, where in our trials at SEPAC [Southeast Purdue Agricultural Center] since 2010, 50,000 plants per acre has been the highest- yielding plant population. We thought maybe it was related to variety, so we put that low target in a variety trial in 2015, and still saw the same results. In 2015, 50,000 plants per acre at that site yielded 68 bushels per acre. We’re not sure exactly why such a low population excels there. Yes, the stems are big, but you can still cut them with a regular cutter bar.
You wouldn’t recommend that anyone choose a target stand that low, would you? Absolutely not. You don’t have much room for error at that point. You also have to think about weed control and closing the canopy. When assessing potential replant situations across the state, however, if there are 70,000 plants fairly uniformly spread without big weed issues, I would recommend leaving it.
Where does the type of equipment used to plant fit into this equation? Recognize that different types of planters and drills do a better job of placing seed at the correct depth, and perhaps the correct spacing, than others. Germination tends to be better with equipment that spaces it precisely.
As a rule of thumb, if your target final stand is 100,000 to 120,000 plants per acre, I would seed 120,000 to 140,000 seeds per acre with a planter either in 15- or 30-inch rows. If you’re using an air drill, move it up to 140,000 to 160,000 seeds per acre. If it’s a regular no-till drill, shoot for 160,000 to 180,000 seeds per acre.