Just because you applied N before planting or at planting and have had lots of rain doesn't mean your field is automatically in trouble. Part of it depends upon when it was applied and what form it was applied in. It also makes a difference whether an N stabilizer was applied or not. That's typically N-serve for anhydrous ammonia, which holds the N in a form that breaks down more slowly, and Instinct for liquid N and urea. Instinct, from Dow AgroSciences, just received an emergency 24(c) label a few days ago to allow it to be applied in applications, even sidedressing applications, this spring.
Some sources suggest testing to see how much nitrogen is out there. However, Dave Mengel proved many years ago that in the Eastern Corn Belt, including Indiana, the tests that require you to test soil one foot deep are not reliable, primarily because we receive more rain than they do in the western states. The main place where most agronomists agree soil sampling for nitrogen before sidedresing can help is in situations where you have applied manure, or another organic source of nitrogen. If you applied commercial N in the form of anhydrous ammonia or another N product, soil testing is not likely to be a helpful indicator of how much N is left in the soil for the crop to use yet this season.
Several companies are also making optical sensors. The theory is that mounted onto applicators, they sense the nitrogen level in plants, and can signal adjustments in rates. The problem is that there is limited university testing on these types of tools. Bob Nielsen and Jim Camberato have tested at least two types of sensors for the past several seasons. They are convinced that the technology works, but have yet to establish guidelines for how much N to apply based on readings they get from the sensors.
Meanwhile, and although it may not help you this year, seed companies are developing hybrids that are more efficient at using nitrogen that is remaining in the soil. Pioneer Hi-Bred International reports that they are using both native genes and transgenic genes to come up with hybrids that will utilize nitrogen more efficiently.
Their goal, says John Shanahan with Pioneer, is to develop hybrids that utilize nitrogen more efficiently because it is good both economically and environmentally.