How Many Soybeans Do You Need for top yield?

Cut back on seeding rate may save seed.

Published on: Feb 21, 2011

If you follow the recommendations in the Purdue University Corn & Soybean Field Guide, 2011 edition, you'll still be planting over 200,000 seeds per acre in solid-seeded fields, and about 165,000 in 12-20 –inch row systems. Do you really need to plant that much seed per acre?

Why would you want to plant less? At 140,000 seeds per $45 unit, each 1,000 seeds cost you about $0.32. If you could back off 25,000 seeds per acre, you would save $8 an acre. On 1,000 acres, that's $8,000.

Planting the extra seed is cheap insurance you say. Truth is that experts, including Purdue University's Shaun Conley, say the recommended seeding rates still carried in the field guide have tremendous insurance built in already. They assume 90% germination, and that 90% of those that germinate will emerge. Under most modern systems, especially reduced tillage where crust can be limited, those numbers are usually higher.

Second, there's another table in the Guide that while placed there to help make replant decisions, is rather revealing. If you get 120,000 plants in solid stands, you can expect 100% yield. Even at 80,000, it's 96%. On 30- inch rows, you can still expect 100% at 80,000 plants per acre. So 15-inch row plantings at 100,000 plants per acre, assuming consistent spacing and adequate weed control, should be near 100% of normal yield.

Even if you get the conservative, time-honored 81% germination by emergence combination, developed before modern planters and more precise controls were common, dropping 140,000 seeds could produce more than 113,000 plants per acre.

One northern Indiana farmer says he used to go 170,000 or more in 15-inch rows, but he's followed company recommendations and backed off to 140,000 seeds per acre. While it made him uneasy at first, he's been very pleased with yield. They definitely haven't dropped off due to plants per acre.

The truth is soybeans have a tremendous ability to compensate. Most agronomists believe the high seeding rates at today's high seed costs deserve a second look. If you're willing to set your planter or drill correctly, choose high quality seed with a germination score, and make sure you're doing a good job of planting, then going to the higher seeding rates may no longer be necessary. Even some seed companies are advocating that people cut back on seeding rate and concentrate on doing the best job they can of making every seed count.