Soybean seed size is influenced by both genetics and the environment. Genetic effects on seed size are largely predictable but weather conditions and their effects on seed size are not. Given the atypical growing season in 2012, it is important to understand the impact on soybean seed size and shape. 

In response to drought, soybean plants typically drop flowers and pods, reduce seeds per pod, abort seeds within a pod, and reduce the size of the seed. The specific response depends on the soybean stage of development and severity of the drought stress. The onset of late season rains caused seeds remaining in drought-stressed pods to swell, resulting in larger than normal soybean seed size.  
 
To help growers manage larger soybean sizes, DuPont Pioneer conducted plantability tests of 2012-produced soybean seed using seven different planter metering units. In collaboration with equipment providers, Pioneer offers management tips to help growers maximize planter performance and ensure the highest possible planting accuracy with larger soybean seed.

• Planter lubricants: Mixing planter lubricants such as talc, graphite or a blend, specific to planter type, with soybean seed is critical.
• Seed treatment: Generally, larger seed combined with treatment will require a higher level of management. Tank pressure, fan speeds and other adjustments should be made for the specific seed and treatment combination being planted. Refer to the planter operator’s manual for recommendations.
• Ground speed: High population settings, especially when combined with high ground speed, may provide challenges. The metering units operate faster with higher ground speeds, making it more challenging to keep seed in place as the unit rotates.

Additional tips based on specific seed metering by planter type are available online in a recent Field Facts from Pioneer.