With the recent rainfall events, now is a great time to make sure that the nitrogen you applied earlier is still there. 

Jim Fawcett, ISU Extension Agronomist, posted some comments about doing this www.iowafarmertoday.com/blog/?p=732

The Iowa Soybean Association, through their On-Farm Network, has some great information on the impact of spring rainfall on nitrogen.  You can review their 2010 Conference Presentations here http://www.isafarmnet.com/2010OFNConfPresentations/ofnpresentations.html.  Iowa's guide for nitrogen recommendations is http://www.extension.iastate.edu/Publications/PM1714.pdf 

Ohio State University has 5 questions to Help Evaluate Your Nitrogen Loss http://cornandsoybeandigest.com/inputs/fertilizer/five-questions-evaluate-nitrogen-loss-0525/

Remember that plant available sulfur is in the sulfate (SO₄)^- form, which makes it susceptible to leaching.  Make sure to include some sulfur (like SuperCal SO4) in your sidedress application!