ISU Extension: How Plant Date Affects Iowa Soybean Yields

Major drawdown by mid-June.

By Meghan Vick

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November 16, 2020 10:07 PM

With more rain moving through the Corn Belt today, there is increasing concern about soybean planting progress and even the need for some replanting. Iowa State University Extension offers some valuable resources for making these decisions, including the following table that breaks down the effect of planting date on yield in Iowa:

Interaction between planting date and maturity group on physiological maturity date, days from VE to R8, and relative yield for soybeans grown in Iowa, 1997

Planting dates	Maturity group
	2.2					2.5					2.9
	Date^a	Days^b	Relative^c		Date		Days		Relative		Date		Days		Relative
	Yield (%)				Yield (%)						Yield (%)
Late April	9/30	137~		100	9/17			132		100		9/25		131		100
Mid-May	10/3	134		96	9/21			118		91		9/25		126		88
Early June	10/5	116		91	9/26			107		72		10/1		111		75
Late June	10/14	108		67	10/2			99		61		10/6		103		54
Early/mid-July	10/14	104		61	10/15			95		38		10/15		99		40

^a Harvest date (month/day).

^b Days between growth stages VE to R8.

^c Relative yield = percent of potential yield for the average of six varieties.

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