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Soybean Planting Depth
With soybean planting just around the corner, now is a good time to consider planting depth. Iowa State University Extension and Outreach recommends planting soybeans at 1 to 1.5 inches deep in Iowa, but no deeper than 2 inches.
Ultimately, soybean planting depth should be field specific and based more on soil conditions at the time of planting. For example, soil moisture, soil temperature, soil texture, and the weather forecast following planting should all be considered when determining planting depth.
Seeds, whether soybean or corn, are exposed to fluctuations of both soil temperature and moisture, and the magnitude of this fluctuation can be influenced by planting depth. Shallow planting depths (less than 1 inch) typically experience greater soil moisture and temperature fluctuations. However, soil temperature fluctuations are less problematic for soybean due to later date of planting.
Well-drained and lighter soils with low organic matter will dry out more quickly than high organic matter or poorly drained soils, potentially resulting in seeds placed in dry soil. A good rule of thumb is to place seeds into a zone of moisture soil, but not too deep, rather than into dry soil that would hinder imbibition of water by the seed. Tilled fields can present the risk of soil crusting, especially with fine-textured soils such as silty clay or clay loam soils, after rain events. Crusted soils can reduce plant populations following planting because the hypocotyls may break from pressure against the soil crust or carbohydrate reserves may be exhausted prior to emerging through crusted soil.
Planting too deep (more than 2 inches) puts the soybean seed at risk of running out of carbohydrate reserves before emergence and increased risk for infection from soil pathogens. Poor seed quality as well as some soybean varieties are at greater risk of pathogen infection or carbohydrate reserve depletion due to greater time to emergence from deeper planting depths.
A starting point for soybean seeding depth should be 1.5 inches but understand the influence of soil temperature, moisture, and texture as well as tillage. Be willing to adjust planting depth for ideal germination in each of your fields.