Are soybeans affected by delayed planting similar to corn? The rainy weather has prompted that question from several northern Illinois producers.

The question can be addressed from recent soybean yield response to planting date trials at the University of Illinois Agronomy Research Centers near DeKalb and Monmouth. In these studies, yields decreased by 0.10, 0.23, 0.36, and 0.54 bushels per day of delay for the May 1-10, May 11-20, May 21-30, and June 1-10 periods, respectively. These results were similar to studies conducted in Indiana.

Another way to evaluate the importance of planting date is to consider the statewide average annual yields in relation to dates of planted soybean acreage, notes Vince Davis, University of Illinois Extension soybean specialist. Over the last 14 years, there has been a loss of approximately 5 bushels per acre for statewide yield averages as the date of planting is delayed from the second week of May to the middle of June. According to the Illinois Agricultural Statistics Service, average state yields were 50, 46.5, 48, 43.5, and 47 bushels per acre for 2004 through 2008. Davis notes that only 50 percent of Illinois soybean acres were planted before mid-May and 80 percent before the end of May, during that same time period. As soybean producers try to improve yield, one strategy is to target planting for early to mid-May suggests Davis. Obviously, Mother Nature has the final say.

Further details on the above-mentioned study can be found in the May 1, 2009 issue of the University of Illinois Pest Management & Crop Development Bulletin, http://ipm.illinois.edu/bulletin/article.php?id=1107