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How Many Soybeans Are Enough?

How Many Soybeans Are Enough?
Time to make gut-wrenching replant decisions.

One farmer who talked to his crops consultant and found out his average soybean counts for most fields were about 140,000 plants per acre winced when he heard the news. "Man, I thought they would be higher than that," he says.

No, you shouldn't really expect them to be. Using the old rule of thumb of 90% germination, 90% emergence, which may be somewhat out of date, the stand would fall in the 135,000 plants per acre range. These are in 15-inch rows. So this farmer actually achieved better than the old standard.

The problem for Extension educators, crops consultants and even insurance adjustors who try to get farmers to leave less than perfect stands of soybeans is that farmers are conditioned to see a field full of young seedlings. The safety factor built into the rates recommended by Purdue University and other sources is so high and has been that high fro so long that farmers have come to expect that type of stand. When they don't get close to what they expect, they begin to worry whether there will be enough plants left to reach maximum yield.

Data collected at various universities and through various trials over time indicate that soybeans don't need nearly as many plants as many people think. In fact, according to the chart in the Purdue University Corn and Soybean Field Guide, published by the Purdue Diagnostic training center, 120,000 reaches 100% potential. Some say even 100,000 seedlings are enough to reach the original potential. And there are those that say that even if the best stand you get is 80,000, you can expect 96% of original yield goal. So if the original potential was 50 bushel beans, at 80,000 plants per acre, now you're looking at 48 bushels per acre. And that assumes anything besides 30-inch rows. In 30-inch rows at 80,000 plants per acre, the yield potential is still 100%.

Reading about 80,000 plants per acre is one thing, seeing them is quite another, But experts say it's enough since soybeans can compensate so fully. The only caveat is that spacing of plants needs to be fairly uniform without lots of long skips, and that you still keep weeds under control. At the lower remaining populations, you won't get as much help from plant canopy than you would at the higher soybean populations.

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