Early or timely planting has been shown to be an important management practice for increasing soybean yields. The benefits of planting early are greater when planting into highly productive soils, planting in wide rows and when drought conditions occur after planting.
The optimum time to plant soybeans in most of Michigan is the first week of May. However, soybeans can be planted during the last week of April if soil and weather conditions are suitable. This practice extends the planting window, but is not expected to increase yields compared to beans planted during the first week of May. Yield losses ranging from 0.3 to 0.6 of a bushel per acre have been reported for each day planting is delayed after the first week of May.
There are several reasons why early planting contributes to higher yields. Early planting typically produces more nodes on the main stem, increasing the potential for more pods and ultimately more seeds per plant. Early-planted soybeans also build a larger crop canopy before entering the reproductive period than later-planted soybeans. The larger canopy captures more of the available sunlight and reduces soil moisture losses due to evaporation by shading the soil surface.
I want to emphasize that early planting is beneficial only when soil and weather conditions are suitable. During the last week of April and early May, soil temperatures are typically not low enough to cause imbibitional chilling injury to the seed. However, the cool soils will delay germination and emergence. Imbibitional chilling injury occurs when very cold soil water is imbibed by the seed within the first 12 to 24 hours after planting.
Producers can significantly reduce the risk of imbibitional chilling injury by implementing the following practices:
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- Plant in the early afternoon to allow soils to warm up.
- Avoid planting when rain is imminent within 24 hours after planting. The heavy rain events that occurred in April and early May 2017 adversely affected soybean germination and emergence in many early-planted fields in 2017.
- Plant later-maturing varieties as they are less susceptible to imbibitional chilling injury than early-maturing varieties.
- Plant high-quality seed having intact seed coats that are free of wrinkles or growth cracks.
- Avoid planting seed having low initial moisture levels.
Soils are more likely to be too wet rather than too dry when planting early. Planting when the soil is too wet can easily negate the benefits of planting early and should be avoided if possible. Sidewall compaction and open seed furrows are the two most common conditions that result from planting when the soil is too wet. Dry weather following planting increases the adverse effects of both of these conditions.
Due to the high probability that early-planted seed will be confronted with cool and wet soils, Michigan State University Extension recommends using fungicide seed treatments when planting early. Select fungicides that are effective against fusarium, pythium, phytophthora and rhizoctonia.
Early planting can be beneficial as long as producers wait for suitable soil conditions, use fungicide seed treatments, plant high quality seed from later-maturing varieties and avoid planting when rain is imminent within 24 hours.