Estimating soybean yields prior to harvest may help producers make marketing decisions, project storage requirements, and determine crop losses from insects, diseases, and weather related stress. However, these estimates typically vary by +/- 25% and should not be used to evaluate the effects that crop management practices or products have on soybean yields. Conducting replicated strip trials combined with statistical analysis is the most reliable and precise way to evaluate management practices and products.
Soybean yield estimates are based on four yield-determining factors; 1) population of pod-bearing plants, 2) average number of pods per plant, 3) average number of seeds per pod, and 4) average seed size. Because these factors change as the season progresses, the accuracy of yield estimates is improved when these factors are determined as close to harvest as possible. The earliest that soybean yields can be reasonably estimated is the R6 growth stage. This growth stage occurs when one pod on one of the upper four nodes on the main stem contains seed that completely fills the pod cavity. However, pods can abort and grain fill can be shortened under stress at R6 so more accurate estimates are obtained at R7, physiological maturity. Physiological maturity occurs when one pod per plant has reached its mature color. A worksheet providing step by step instructions for estimating soybean yields prior to harvest is available at http://www.michigansoybean.org/MSPCSite/GrowerResources/SoybeanYieldWorksheet.pdf.
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. Funding for the SMaRT project is provided by MSU Extension and the Michigan Soybean Checkoff program.