Are you using variable-rate seeding or adjusting plant populations in your corn crop this year? Tweaking plant populations is a common approach to getting more bushels out of each acre. But the potential gains of bumping the number of plants per acre aren't always cut and dried, says University of Illinois agronomist Emerson Nafziger.

The seeding rate, Nafziger says, should stay within that 5,000-seed window on either side of the optimal population and, more importantly, should be based on solid yield map data in order to be effective.

“Variable-rate maps will be OK. None will be perfect — the amount you'll be able to swing out of those acres will be minimal,” he says. “Variable rate is pretty dependent on data gathered in a specific year. After-the-fact summaries show correlations, but the predictive ability remains limited.”

If you are variable-rate planting this year, make sure you use more than one year's worth of plant population maps, especially in areas that faced extreme weather conditions in 2010.

“We have to use common sense with these things — not just the data,” Nafziger says.

“Since many planters can do variable rate and farmers want to use it, they will. The best bet is to set a mid-range population based on response data and economics. From this base, change populations by 800 to 1,000 plants per acre for each 10 bushels in change you expect in yield,” he says.