Issue No. 8, Article 7/May 25, 2012
Soybean Planting and Dry Soils
In some parts of Illinois soils remain dry, and producers are wondering whether to plant soybeans into dry soil. It's a fairly common question, especially with soybeans, because they're more likely to be planted late enough that soils are dry, and they need to take on more water to germinate than corn seed does. Soybean seed also does not draw water quite as strongly as corn seed does.
We know that it's a little risky to plant soybeans deep (let's say deeper than 2 inches) because heavy rain might seal them in before they can emerge. Seed treatments have helped emergence ability, and with the weather pattern we've had there doesn't seem to be much risk of heavy rain. So with soils warm and it staying dry, there isn't much risk to soybean seed planted 2 to 2.5 inches deep.
If seeds need to be 3 inches deep to get to enough moisture, then it's likely that some parts of the field won't come up until it rains anyway due to uneven soil moisture and (probably) seed placement. In such cases it might be better to either plant at normal depth and wait for rain to bring seed up or to wait until after it rains to plant.
The question of whether to plant and wait for rain to bring the crop up or to wait until it rains to plant into moisture is an enduring one. It's almost always better for soybeans to emerge with little no rain between planting and emergence, from the standpoints of both disease and crust formation.
If it rains an inch or so after planting into dry soils and then is not too hot and dry--that is, if we don't have crust-forming conditions--emergence should be okay. On the other hand, if it rains 3 inches after planting then we often will have to replant, in which case having waited to plant looks better. That makes the decision whether to plant into dry soil a tossup, but the later it gets, the more reluctant most people are to wait.--Emerson Nafziger