Updated April 29, 2020:
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This confirms our recommendation that varieties chosen for double crop use should be the same varieties used for full season production.
We have found that yield maximizes in full season soybean production at around 90,000 plants/acre in most years. Results from this experiment confirm that stand densities in double crop system should be greater than full season, although we would predicted that the 130,000 density might yield more than the 105,000 density. The late summer weather during the second year was very dry. That may have limited the yield response to stand density.
Seed treatment increased soybean yield in both years. Average increase was 7%. We’ve never found that seed treatment increased yield of full season soybean. Perhaps stand density is more important for double cropped soybean or some effect on plant health influenced yields.
In-season application of a foliar fungicide increased yields in both years. We did not scout for or identify specific diseases. With a short growing season, protecting leaf area is critical to yield.