A new software program can help you predict how much nitrogen to apply to corn. And it's free.

USDA-ARS soil scientist Alan Olness has created a computer program he calls a "decision aid for fertilizer." He says it will predict N content for up to 90 days after planting by calculating how much has been produced every year, in every field, by every spring.

"Farmers supply the weather information [local temperature and rainfall] for their location," he says. "And they take soil samples and enter results [soil texture,salt pH and density] into the database. The program uses this information to come up with an estimate of how much N is going to be in the soil prior to planting."

Organic matter, the amount of snow and rainfall, and soil aeration/compaction all directly affect the amount of nitrate nitrogen in the soil. "So when we put all these together, we can come up with an estimate for the amount of nitrate that has leached," Olness says. "Then we can come up with the amount of nitrate left in the soil."

For a complete profile of the soil, Olness recommends a preplant soil sample to a depth of 2 ft. He says soil compaction is hard to detect and will show up as an N deficiency even if you've added a lot of N. Olness suggests a soil core to test soil bulk density.

For the first go-around, Olness says to set a critical level for nitrate (usually about 20 parts/million, equal to 160 lbs. of N). He says to keep in mind that a standing corn crop at maturity should contain between 210 to 250 lbs. of N/acre. He predicts you will eventually save 10 to 20% on fertilizer inputs.

The free software program can be used for any crop that needs nitrogen. You can tailor it to your own farming practices. Download the program or send an SASE to Olness at ARS North Central Soil Conservation Research Laboratory, Dept. FIN, 803 Iowa Ave., Morris, MN 56267, 320/589-3411, ext. 100.