Two Year Final Summary
Stressing a soybean mechanically is safer on average than using a chemical stress. Over the two years the Cobra stress averaged 0.7 Bu/ac increase (Figure 10) compared to the control, resulting in an economic loss of $8.14 per acre. Over the six site years the Cobra stress had a positive economic return only twice. Of the two site years with a positive return to Cobra stress one location had moderate to heavy white mold pressure the other site year had soybeans that averaged over 80 Bu/ac. The mechanical stress with the roller at V1 averaged an increase of 2.4 Bu/ac with an economic return of $16.02/ac over the two years. The yield response is due to an improvement in individual plant yield components and a reduction in harvest loss. When evaluating the best timing for rolling over the two years, the V1 timing is optimal. Rolling at V3 breaks
too many plants below the cotyledon, adds too much overall stress to the plant, and often increases harvest loss resulting in inconsistent yield responses with an average increase of only 1.2 Bu/ac compared to the control. The Post-Plant rolling offers reduced harvest loss and increased yields on average 0.8 Bu/ac across the two years compared to the control. About 50% of the yield gained with the Post-Plant rolling is coming from reduced harvest loss; the rest is coming from an improvement in individual plant yield components. However, it is unclear why the Post-Plant rolling is improving the yield components. It may be due to improved plant to plant uniformity at emergence and less plant to plant competition.