Soybean responds significantly to early planting. Despite cold soil temperatures and slow plant growth during the seedling phase, there is a yield benefit from early planting, which seems to be influenced by field yield potential. The yield benefit is a result of increased seasonal canopy photosynthesis, greater number of main-stem nodes, potential for earlier flowering, increased crop growth rate during pod set and greater seed filling rate. Based on 24 experiments conducted across Iowa since 2003 with the support from the checkoff and the Iowa Soybean Association, there is a 79 percent probability of achieving the highest yield by planting the last week of April (southern two thirds of Iowa) or the first week of May (northern one third of Iowa) compared with approximately May 20.
Iowa State University
Pedersen, Palle, "Minimize Soybean Yield Loss from Late Planting" (2008). Integrated Crop Management News. 935.
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