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!