Software program hikes efficiency

Corn growers have cut nitrogen use a bunch - thanks mostly to water quality concerns. Now they have a tool that could cut nitrogen levels even more to reduce environmental risks and save money.

The tool is a computer program created by Alan Olness, a USDA-ARS soil scientist at Morris, MN. He calls it a "nitrogen decision aid." Best of all, it's free.

"Nationally I now see N use leveling off at about 160 lbs/acre, which is substantially less than in recent years," Olness explains. "But we're still overusing it, and could save probably 10-20% more."

Recent research shows we are seriously overusing nitrogen on some soil types and are likely underusing it on others, the scientist says.

"So if we could improve that application efficiency across those different soil types, I think we could get a yield increase on the one hand and less environmental damage on the other from these applications," he says.

The foundation on which Olness built the software program was a recently completed 12-state North Central Region research project that evaluated soil nitrate tests for predicting corn nitrogen response.

The program is based on spring nitrogen application, which research has proved makes more efficient use of the nutrient than does fall application.

Here's how it works. It's recommended that soil samples be taken before planting to determine how much nitrate nitrogen is available in the soil. The decision aid then predicts how much will be there through the time of sidedressing.

The decision aid makes that prediction after the farmer supplies weather information - local temperature and rainfall - for his location. Information from the soil tests, including soil texture, pH, bulk density and organic matter content, are plugged into the decision-aid program.

"By taking into account the climate during the spring, as well as the amount of nitrate nitrogen that is actually found at some point in time with the soil test, we can come up with a pretty accurate prediction of how much N is going to be there when we can sidedress," Olness explains.

The decision aid takes into account the amount of nitrogen generated by the soil microbial community through mineralization. There's also a prediction for nitrogen leaching and denitrification.

The amount of nitrate nitrogen in the soil at the time of the soil test, whether from carryover or mineralization, is then subtracted from a factor of 20 parts per million (ppm), which is equivalent to about 160 lbs/acre in the upper 2' of the soil profile. That gives the amount of nitrogen that needs to be added to reach the point where the crop will no longer respond.

Extensive research in the 12-state study showed that if you have 20 ppm of nitrate nitrogen in the soil profile at the time you'd normally sidedress, you won't get any extra yield by adding more nitrogen.

Usually, the scientists say, at least 40 lbs of nitrogen need to be added. "We found the decision aid predicting as little as 80 lbs of nitrogen needed up to 120 lbs within the same field as we went from one soil type to another," Olness says.

What about supplying some nitrogen as starter for faster early growth, especially under less-than-ideal conditions?

"We generally see a benefit to starter nitrogen fertilizer," Olness says. "If we have a cold, wet spring, I'd put on a little more. We've been using 10-15 lbs of starter nitrogen and it seems adequate here."

The amount of nitrate nitrogen in the soil in spring can vary drastically, depending on soil type and weather. That's why it's important to soil test for it in spring.

"Normally we see an increase in nitrate nitrogen in spring, and it can be anywhere from 40 to 100 lbs/acre out there," he points out.

Nitrogen offers a good payback regardless of price. But even though there has historically been a price advantage for fall-applying nitrogen, interest in making nitrogen use more efficient is growing.

The free decision aid has been downloaded to every country in Europe, plus China, Vietnam, Australia, New Zealand, South Africa and several countries in South America, reports Olness.

You can download the program from www.morris.ars. usda.gov. Follow the Computer Software Products link to the Nitrogen Decision Aid link.

Or send a self-addressed, stamped envelope to Olness at: ARS North Central Soil Conservation Research Laboratory, 803 Iowa Ave., Morris, MN 56267. He can be reached at: 320-589-3411, extension 100.

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