Today most soybeans are seeded with a conventional planter. There are still some growers that use drills and air seeders because they are planting cereals or they are planting double crop soybeans and want a high population and narrow rows.
When it comes to planting soybeans no one thinks much about the planter and what it is required to do since they are more concerned that corn gets planted right. And if a planter can plant corn seed right then it will work fine for soybeans – which is generally true.
For corn, seed needs to be singulated and placed precisely at the same depth and same distance apart and covered and firmed with soil around it without creating any sidewall compaction or placing the seed into a ball of crop residue. All of the same principles can be applied to seeding soybeans but it is less critical since growers are planting 5 times more seed (30,000 vs. 150,000) and soybean plants can flex and compensate for gaps between plants. And this ability to compensate means growers can be less particular about how precisely they place soybean seed in the soil.
However, as soybean seed and seed treatments increase in cost and commodity prices remain on the low side, growers can reduce their seed rate to save cost and by precisely planting seed in the right soil conditions (moisture, temperature and structure). It has been determined that the maximum plant population at harvest to optimize yield is 100,000 plants per acre. But the decision on how many seeds to plant to achieve 100,000 at harvest is personal and that population could range from 120,000 to 160,000. But following the same objectives you have for corn you could reduce your planting population.
Fortunately corn seed is sold based on size and shape so you can adjust your planter and vacuum settings accordingly. Unfortunately soybean seed size is irregular and while you may know the average number of seeds in a lb. (2000 to 3000) that is all you know. And remember seed size is greatly influenced by the weather during production. A dry year will produce small seed while a wet and cool season will produce bigger than normal seed.
Planter manuals provide guidelines for successful planting of various seed sizes. In general, what to look for is soybean seed size and is it larger or smaller than normal or average and then use the appropriate settings. And most planters require talc or graphite as a lubricant that allows seed to be more consistently released from seed disks and other planting mechanisms.
Regardless of planter type, calibration steps and field checks should be done prior to full-scale planting. Run the planter in approximate field conditions to observe for planting accuracy. Once in the field, stop after reaching planting speed for a distance and check seed drop, spacing, depth, covering and firmness. Even though a pre-season planter check was made, all of these items should be rechecked when actual planting begins and as conditions change during the planting season.
How do you approach setting up your planter for seeding soybeans in the spring?
Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org.