Katharine Parker, Crop Physiology, University of Illinois, Champaign-Urbana, IL, Ross R. Bender, Mosaic Company, Cleveland, WI and Frederick E. Below, University of Illinois-Urbana-Champaign, Urbana, IL
Due to the indeterminate growth of soybeans (Glycine max), the soybean plant has an extended period of pod development, approximately growth stages V7 through R5. Therefore, it is important to manage the soybean crop during this time to prevent stress that causes pod abortion and potential yield loss. The objective of this experiment was to determine if agronomic management practices could alter yield components throughout the soybean canopy. Early and full-season varieties were subjected to several management practices: i) fertility [natural fertility (none) vs 75 lbs P2O5 per acre banded at planting], ii) foliar protection (none vs insecticide and fungicide applied at R2), iii) a combination of fertility and foliar protection, iv) a plant growth regulator (Megafol applied at V5 and Ascend or Utilize applied at R2), or v) a combination of fertility, foliar protection and a plant growth regulator. The trial was conducted at Champaign and Harrisburg, IL. Repeated quantitative measurements on seed mass establishment and final seed yield at the upper, middle, and lower nodes were used to determine seed growth rate and seed filling duration. Additionally, the numbers and canopy position of pods, seed yield, yield components and seed quality were measured to assess the impact of the various management treatments. Fertilization increased the number of seeds at the middle and top soybean nodes and led to an increase in seed weight at the bottom and middle nodes. Foliar protection increased the number of seeds at the top nodes and increased seed weight in the middle and top nodes. In the early season variety, yield increases were achieved by an increase in the number of seeds. Conversely, greater yields in the full season varieties resulted from an increase in seed mass. Using variety selection and agronomic management can lead to yield component increases throughout the soybean canopy.