You won’t find too many farmers who would disagree with the notion that corn plant health can vary widely across a field. And I think the majority of growers would love to improve their nitrogen fertilizer use efficiency—if only the weather would cooperate.

While variable rate fertilizer based on grids/management zones and soil tests is one possible solution, that practice cannot account for heavy spring rains—all too familiar to growers in some Midwest states during the past two years. These events caused a lot of N loss through nitrification, runoff and leaching. Peter Scharf, University of Missouri Extension agronomist estimated that 70 million bushels of corn were lost in his state in 2008, and even more was lost in 2009.

However, using sensors to read and apply the correct amount of N a plant needs at V6 growth stage is a technology that is beginning to catch on. But in order to reap potential benefits, growers must be willing and able to apply one-third to one-half of their target N amount pre-season, then come back and sidedress, feeding the healthy plant less and the weaker plants more.

A handful of companies have developed the technology, with Ag Leader Technology being one of them. Over 100 side-by-side comparison tests (sensor-applied versus grower’s normal flat rate) at the University of Missouri USDA-ARS have shown an average benefit of $15 to $20 per acre with sensors. Ag Leader trials with their OptRx crop sensor system delivered $50 to $60 per acre greater return in 2008, and a $22 per acre average return last year.

“We don’t expect such high returns year in and year out, unless high rainfall removes N early on from the profile, like it did in 2008 and 2009 in many areas,” says Chad Fick, OptRx product specialist for Ag Leader. “We have great confidence with the sensor, now it’s all about getting more growers to experience the possibilities in their fields.

Fick says they have conducted trials in Iowa, Missouri, Kansas, Illinois, Indiana, Michigan and Louisiana. “We’ve had good results in all cases except in Michigan where we didn’t get harvested grain data due to the corn being chopped. Most growers applied approximately 60 to 100 lbs N before planting, then came back at the V6 growth stage to sidedress the amount needed by the crop, as determined by the sensors,” he says. “The most important emphasis here is to make sure you have enough N so the crop does not get stressed before V6—because stress before then will cause permanent yield loss.”

To calibrate the sensors, Fick says it’s as simple as driving to the healthiest part of your field and taking a reference strip sensor reading there. “That gives the sensors a frame of reference to what the field is capable of achieving.

If you want to hear comments from several growers about their experience with this technology, check out the video on this page.