Management recommendations for large soybean seed

Large soybean seed may create some challenges. Understanding the challenges and the strategies for overcoming them will improve seed performance in 2013.

Due to the 2012 drought, the size of the soybean seed available for planting in 2013 will be highly variable. In some cases, the drought reduced the size of the seed, but more often it created larger seeds. Soybean plants abort blossoms, pods and seeds in response to stress during the reproductive stages. In many areas, the rains came too late for the plants to produce new blossoms, so the plants put their resources into increasing seed size. Seed size within a given variety can vary by as much as 20 percent and some of this year’s seed will have 200 to 400 fewer seeds per pound. Within a given variety, seed size does not affect the yield potential. However, the large seed may cause some management challenges for producers. Understanding these challenges and the strategies for overcoming them is critical to maximizing seed performance in 2013.

The first step is to determine the size of the seed for each of your seed lots. The next step is to seek information from your operator’s manual, seed supplier and equipment dealer about equipping and setting your planter or drill to handle this year’s seed sizes. Michigan State University Extension says taking these steps now will prevent problems at planting. Large seed (2,400 seeds/lb. or less) can be damaged by the fluted metering system in drills. This type of damage can be reduced by plugging every other feed cup and opening up the seed metering gates. Some drills allow the feed cup to be lowered, increasing the space between the fluted seed metering mechanism and the bottom of the feed cup. Check your operator’s manual for specific recommendations.

Another potential concern with large seed is that the seed may have enlarged so quickly last summer that it caused growth cracks in the seed coat. Growth cracks allow the seed to imbibe water too quickly, increasing the potential for the embryo to experience chilling injury when planting into cool soils. Seed with growth cracks is also more susceptible to mechanical damage during handling and transport and will lose vigor faster than intact seed. Careful handling and transport of the seed and waiting to plant into ideal conditions are the best management strategies for seed exhibiting growth cracks.

Large seed has larger cotyledons that must be lifted out of the soil during emergence. This may cause emergence problems on fine-textured soils prone to crusting. Planting the seed in wide rows is usually beneficial as the soyeans are spaced closely enough within the row to crack the crust. In some cases, a timely rotary hoeing may be required to break the crust. The loss of one cotyledon on a few plants during emergence will not affect yield. However, if a large percentage of plants lose one or both cotyledons, yields will be significantly reduced.

All soybean seed must imbibe 50 percent of its weight in water during germination. Large soybean seed must imbibe more water to germinate than small seed. This may lead to delayed or uneven emergence under marginal soil moisture conditions. Most agronomists recommend planting soybean seed into at least one-half inch of moist soil to promote uniform germination and emergence. This recommendation is even more important with large seed.

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between MSU Extension and the Michigan Soybean Checkoff program.

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