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Try lower soybean seeding rates

Suppose you pay $45 per unit of soybean seed. Each unit contains 140,000 seeds. So soybean seed cost you 32 cents per 1,000 beans. If you plant 175,000 seeds per acre, seed cost equals $56 per acre.

If you plant 130,000 instead, it’s $43.20. On 1,000 acres that amounts to a savings of $12,800. The biggest question is: Can you plant 130,000 seeds per acre without hurting yields? Shaun Casteel, a Purdue University Extension agronomist, is looking closely at that question.

Key Points

Figure your seed costs in cost per 1,000 seeds.

The current recommendations have a large fudge factor built in.

Cutting seeding rates about 35,000 seeds per acre could save over $11 per acre.


Casteel will work with cooperators to put out trials to determine how thick populations must be to obtain maximum yields. If you’re interested in participating, check with your local Extension ag educator.

Suggested planting rates

Currently the Purdue University Corn and Soybean Field Guide, 2011 edition, makes these recommendations: For drilled, solid-seed soybeans, the target population is 168,020 plants in 7-inch rows. For 12- through 20-inch rows, it’s 130,680 plants per acre, and for 30-inch rows, it’s 104,540.

Purdue charts have assumed 90% germination and 90% emergence. With better varieties and improved seeding equipment, higher percentages may be possible.

If you’re in 7-inch rows, that translates into planting 207,000 seeds per acre; in 15-inch rows, it’s 161,000 and in 30-inch rows, 129,000.

Some seed companies push much lower seeding rates. There are two issues — can you achieve better than 90% germination and 90% emergence? And how thick must stands be?

Yield data dating back to the 1980s suggests that there’s a large safety factor built into soybean seeding rates. That assumes weed control is not an issue and that stands were fairly uniform.

Based on this data it’s possible to maintain 100% of yield potential at 120,000 plants per acre in solid-seeded fields and 30-inch rows. At 80,000 plants per acre, a stand that most people would tear up, there’s still 96% yield potential for solid seeding and 100% for 30-inch rows.

The implications are huge. For example, if new trials determine that 100,000 plants per acre in solid-seeded or 15-inch rows maintain 100% yield, then the seeding rate could be less than 125,000 seeds per acre.

Test your yield goal knowledge

A hailstorm left only 40,000 healthy soybean plants per acre. That’s only slightly more plants per acre than some corn growers hope to get. If your original yield goal was 60 bushels per acre, how many bushels could you expect to harvest if you leave the stand, assuming weeds are controlled?

Give up? The answer, according to the Purdue Corn and Soybean Guide, is 52.8 bushels per acre!

Never give upon the soybean’s ability to compensate. Especially in replant situations, this ability to compensate plays an important role in your final decision.


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Enough plants? Is this stand good enough? Actually, it was 140,000 plants in 15-inch rows. The field made 54 bushels per acre, despite virtually no rain in August.

This article published in the April, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.