By Darren Hefty
When it comes to planting population, soybeans are a little tricky. We get asked about lowering planting populations all the time. If lower means 140,000 seeds per acre to you, then I’d agree that’s a good place to start in most situations.
Why Lower Populations?
- Less cost
- Soybeans have the ability to bush out and fill in if there are gaps in your stand.
- Lower planting populations, especially in narrow row soybeans, can sometimes yield just as well as higher populations.
- Less disease pressure.
It may sound like I’m a proponent of lower soybean populations. However, you really need to be careful not to cut them too far.
Reasons to Plant Higher Populations:
- Germination – Soybean seed quality is considered good when it is above just 90% germination. To make matters worse, the cold germination (cold germ is not monitored by most seed companies, nor is it on the seed tag) may be 80%. This is a common number we have seen in our seed testing lab over the years. That means 10% to 20% of your seed may not make it out of the ground. All of a sudden your 140,000 planting population could be 126,000 or 112,000, and we wouldn’t call that out of the ordinary.
- Emergence – If your field has surface crusting or any other factors that would make emergence difficult, your plant stand can get thinned out before it ever really starts. As soybeans are about to pop out of the ground, the two halves of the seed become the cotyledon leaves. It is not unusual for a cotyledon leaf to get pulled off if emergence is challenging for your soybean plant. If both cotyledons fall off as the plant is coming out of the ground, your plant will most likely die.
- Vulnerability – Another disadvantage soybeans have is the fact that the growing points are all above ground as soon as the cotyledons emerge. Insects and unfavorable weather (e.g. hail, strong wind, etc.) can quickly lead to stand loss.
- IDC – Iron Deficiency Chlorosis issues seem to be lessened when planting populations are higher.
Soybean summary: While you may read or experience a situation where a final stand of 80,000 plants still got excellent yields, more times than not you need more plants to get the performance you’re looking for. In our research in the upper Midwest, higher plant stands all the way up to 300,000 have yielded the best, but the extra seed cost didn’t justify planting that thick. From what we have seen, 120,000 to 140,000 final stands appear to be the range to hit.