What’s the right seeding rate for soybeans?

I am in Ukraine on a training mission to assist growers here in growing better corn and soybeans. One question that keeps coming up is, “What is the right seeding rate for soybeans?” Some of them have told me that it’s 1 million seeds per hectare. I think in terms of 1 million for wheat, but a hectare is 2.47 acres, so 1 million is 405,000 seeds per acre — still too high. Take into account that they use brown bag seed, so add maybe 20% due to reduced quality seed — still too high. And oh, by the way, this brown bag seed seems to tolerate very high levels of “gleefosat” herbicide applied over the top.

I give them the same answer I do when the question comes up in Ohio — we need about 100,000 plants per acre at harvest to achieve full yield. You just calculate backwards to determine your losses to germination percent, emergence, disease, insects, crusting, excessive moisture, etc. to determine your seeding rate. For central and southwest Ohio, something around 130,000 to 150,000 seeds per acre is about right. In the lakebed soils of northwest Ohio, maybe closer to 200,000 seeds per acre is about right. But every farm could have a different seeding rate, and probably does. One way to find your seeding rate is to conduct an on-farm trial.

At the Farm Science Review University farm site, the question of seeding rate came up and the additional concern of how vertical tillage may change this question. We conducted our own replicated trial in 2013. With RTK and on the go variable seeding rate capability, it’s pretty easy.

 

Table 1.  Tillage effects on plant lodging, plant stand and soybean yield, London Ohio 2013.
Tillage typeLodging      (1-10)Stand            (thou. pl/A)Yield (bu/A)
No-till2.199.757.2
Vertical tillage2104.659.3
LSD (0.05)NSD1.20.7

As you can see in Table 1, the vertical tillage tool does improve our stands a little. But from past trials, the difference between 99,700 plants per acre and 104,600 is not agronomically significant. Yield is a little higher by about two bushels per acre, but when we factor in the cost of the tool, the time to run it, and the fuel, it may not be economically advantageous. You will have to decide that.

 

Table 2. Economic impact of seeding rate on net return per acre, London, Ohio 2013. Soybean price here is $13 per bushel.
Seeding rate (thou. sd/A)Yield (bu/A)Seed cost ($/Acre)Gross ($/Acre)Net return (less seed cost)
5051.2$20.36$665.60$645.24
10057.4$40.71$746.20$705.49
15059.6$61.07$774.80$713.73
20061.4$81.43$798.20$716.77
25061.7$101.79$802.10$700.31

 

Look to Table 2 for the seeding rate differences. We can see easily that the 50,000 seeding rate is too low. We have a 6-bushel advantage to adding 50,000 more seeds to get to a total seeding rate of 100,000 seeds per acre. Add another 50 thousand and we jump by only two bushels per acre at 150,000 seeding rate. And economically we are at $714 return. So while not agronomically the highest yield, economically at 150,000 seeds per acre we arrive at (roughly) our highest return. Our stand count for this seeding rate comes in at 101,300 plants per acre and that’s close enough to our target of 100,000 plants per acre.

Here is a simple trial we will encourage you to consider on your farm. Invite the local Extension educator to work with you on this too, and we all win.

Treatment targets:

  1. 60,000 viable seed per acre based on germination
  2. 95,000
  3. 130,000
  4. 165,000
  5. 200,000
  6. 235,000

Experimental Design: Randomized complete block with minimum of three replications, shown in Figure 1. Plot width will depend on cooperator’s equipment: planting, and harvesting. Plot size 1.5 to 2 times the width of the combine header will maximize harvest efficiency. Plot length should be a minimum of 350 feet. Take a stand count after 30 days, then harvest with a yield monitor.

 

Figure 1. Sample plot arrangement:

 Replication 1Replication 2Replication 3 
Border352146514263261534Border

 

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