Does Precision Soybean Seeding Pay?

Traditional seed drills do a poor job of distributing seed evenly, resulting in seed clumping, that leaves large gaps within the row. This is shown in Photo #1. A planter that allows for precise seed metering results in more uniform stands. It also allows for better depth control.

There has been speculation that more accurate seed placement may allow for lower seeding rates compared to a drill and result in higher yields. In the case of glyphosate tolerant varieties, soybean seed has become the largest single input (approximately $50/acre). Lower seeding rates could significantly reduce this input cost.

Photo #1 - Emerging seedlings seeded with a no-till drill

Drill Versus Planter - Seeding Rate Study

In 2005 and 2006 a study investigated the most profitable soybean seeding rate for 15 inch row spacing using a row planter. It also compared 15 inch rows seeded with a planter, to 15 inch rows seeded with a drill and 7.5 inch rows seeded with a drill.

Eight large scale replicated trials were conducted. Various 15 inch row planters were compared to a JD 1560 no-till drill with every other run plugged (15" row spacing) and all runs open (7.5" rows). All sites were no-till and different seeding rates were tested.

Results and Summary

Graph #1 - Impact of Planter/Drill Seeding Rates On Yield

P = Planter (15" rows), D = Drill (15" rows), S = Solid Seeded Drill (7.5" rows), LSD 10% = 1.9

Link to data equivalent chart

Planter Versus Drill Results

Although the planter units did a superior job in seed distribution, that did not translate into higher yields compared to the drill at the same seeding rate. The 15 inch drill produced equivalent yield to the three seeding rates as did the 15 inch planter averaged across all sites. At 1 out of the 8 sites there was a 3 bu/ac advantage to the planter. At all the other sites the increased accuracy of the planter compared to the drill had no significant impact on yield. 

This is surprising, especially at the lowest seeding rate. Thirty days after seeding the planter rows looked superior because of better spacing. But the gaps resulting from using the drill did not reduce yields. This is likely because of the soybean plant's ability to compensate for gaps and may also be a reflection of the good growing conditions over the last two years. We intend to conduct these trials one more year before final conclusions are drawn. 

Keep in mind, that a planter is superior when using very low seeding rates. This has been shown in other research studies. Under extremely low seeding rates (50 000 - 100 000 seeds/acre) the planter will provide significantly better yields compared to a seed drill.

Seeding Rate Results

This study has also demonstrated increased yields with increasing populations from 150,000 to 200,000 seeds/acre. When seeding rates were increased, yields increased.

It's worth noting that the benefit from increasing the seeding rate was different for the planter compared to the drill. Raising the seeding rate from 150,000 to 200,000 with a planter only increased yields by 1.3 bu/ac. Increasing the rate from 150,000 to 200,000 with a 15 inch drill increased yields by 2.1 bu/ac. Increasing the seeding rate from 150,000 to 200,000 in 7.5 inch rows increased yields by 3.5 bu/ac. This confirms that higher seeding rates are important for drills but not as crucial for planters.

Assuming a seed cost of $32 per unit, a seed size of 2,700 seeds/lb, and a selling price of $7.00 per bushel, the return for increasing the seeding rate from 150,000 to 200,000 seeds/acre is significantly different for the two pieces of equipment. Increasing the seeding rate for the 7.5inch drill increased profits by $12.65/acre. Increasing the seeding rate for the 15 inch drill increased profits by $2.85/acre. However, increasing the seeding rate with a 15 inch planter actually reduced profits by $2.75/acre.

Numbers based on $32.00/unit, 2700 seeds/lbs seed, $7.00/bushel selling price,
and yield results from Graph #1. All inputs except for the cost of seed are assumed to be the same regardless of seeding rate and are not included in this comparison.

Conclusions

1. At normal seeding rates (175,000 - 200,000) there was no significant yield difference between the 15 inch planter compared to the drill seeded in either 7.5 inch or 15 inch rows.
2. Lower seeding rates yielded less than higher seeding rates in this study but reductions were relatively small.
3. The highest yield was at 200,000 seeds/acre for all three implements
4. The highest economic return for the drill was at 200,000 seeds/acre but was 150,000 seeds/acre for the planter.

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