With anhydrous prices shooting off the charts and other nitrogen (N) sources following the trend, taking a few minutes to figure N loss could save you hundreds or thousands of dollars in the future.
“The price of N is very high and farmers want to know if they can reduce their rates,” says Ed Lentz, Ohio State University agronomy specialist at Tiffin.
Reducing rates begins with figuring N loss. Ohio corn and soybean grower and consultant Bill Lehmkuhl helps fellow farmers figure N losses.
Although there are new sensing tools, Lehmkuhl prefers the pre-sidedress nitrate test (PSNT) because it's quick and easy. The late-spring test helps take the guesswork out of sidedress rates. To start, take soil samples when the corn is 6-12 in. tall. “This timing is very important,” Lehmkuhl says.
Another way to increase the result's accuracy is to sample at one-foot depths. The test is sent to soil test labs and if the values are 25 ppm or higher additional N is usually not needed.
The trick is knowing your crops and soils. Evaluate your own fields carefully, says the Minster, OH, farmer. N loss depends on many factors such as soil texture, type of hybrid, soil fertility and rainfall. Ponding or flooding can cause N loss through leaching and denitrification.
Even in dry weather N can escape. Surface-applied urea fertilizers can volatilize as gaseous ammonia (NH3) during dry conditions.
“You can apply 30-40 lbs. of N to parts of fields that show symptoms and hope that's enough, but not too much,” points out Bart Lofton, technical service agronomist from Golden Harvest Seeds in Indiana. But taking a few minutes to figure loss can pay.
Although estimating N loss isn't an exact science, it can be a useful tool to predict when N is needed. Estimating N loss is a risk reducer, Lofton points out.
Deciding how much N to add depends on finances and yield goals. Whatever method you use, a rough idea is better than no estimation at all, experts say.