Cha-ching. Every day beyond May 1 limits the yield you could realize on soybeans, according to recent studies in Nebraska. Research conducted by University of Nebraska—Lincoln agronomist Jim Specht shows soybean yield declines by ¼ bu. per acre to 5/8 bu. per acre per day for every day after May 1. In 2008, three on-farm comparisons, and one at the South Central Ag Lab near Clay Center, confirmed the trend.
As a broad recommendation, Specht and Clay County, Neb., Extension educator Jennifer Rees recommend planting soybeans the last week of April in the southern two-thirds of Nebraska and the first week of May in the northern third of the state.
You need to consider the risk of a late spring freeze in your area when selecting your planting date, Specht and Rees note. You can find weather data at the High Plains Regional Climate Center site: http://www.hprcc.unl.edu
. Click on Historical Data Summaries
. Then find the red dot representing the weather station closest to your farm. On the left-hand side, find the section titled Temperature, and click on Spring Freeze Probabilities.
You can read more about Specht's and Rees' planting-date research at http://cropwatch.unl.edu/archives/2009/crop7/soybean_planting.htm
. You'll also find an article by Specht, in which he questions the methods used in a study recently published in a professional journal, which argued that there is no advantage to planting soybeans earlier than very late May in the Midwest.