Even if you had a somewhat normal crop, it may not have used all the nitrogen you applied, hoping for a good crop in 2012. Some crops couldn't access N due to dry conditions, and others didn't even use it because there wasn't enough grain production. So what will happen to that unused N?
Jim Camberato, Purdue University Extension agronomist, says that you likely still have a good chance to capture at least a significant part of the nitrogen that wasn't used through cover crops, but the sooner they're up and growing, the better. Those that were seeded early by flying on or seeded in other ways will likely have the best chance of getting enough growth to reach and use the N.
Many areas began receiving rain in early August. Some areas have received more than 10 inches in six weeks. Is the N still there?
"Part of it should still be where roots of cover corps could get it," Camberato says. "The soils were so dry that the subsoils are just now starting to 'wet up' in many cases. Where that's the case, if cover crops are out there now and get some fall growth, they can probably capture quite a bit of it before it moves too deep in the profile for roots to reach."
What if you elect not to grow cover crops? What happens to the leftover N? "If we have a normal winter, we will get about 20 inches of precipitation. If we get that much, the N will be washed out, at least below where roots can reach it," he says. "You will basically lose it."
If it's an unusually dry winter then some of the N may still be hanging around next spring, he says. But that would require a winter with considerably less precipitation than normal.