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University of Illinois Nitrogen Test May Be Useful After All

Crops consultant says it works well as part of a system for making N recommendations.

Did you apply enough N this year? Too much perhaps? You won't know unless you visit your fields soon. And then if will be much easier to tell if you applied too little rather than too much. Nitrogen deficient leaves fire down the vein first. Then the leaves turn brown. Firing begins at the bottom of the plant and moves upward as the season progresses.

Just a couple years ago, it seemed like a nitrogen soil test that would work in the eastern Corn Belt was on the horizon. Iowa State University has a test that's been used for years to help make N recommendations, but it's not as effective in the eastern Corn Belt where more rainfall and higher humidity levels tend to skew the results. However, some folks hire consultants that use the pre-sidedress nitrogen test developed at Iowa State to determine how much sidedress N is needed. It works best on soils that have received manure applications, or that are otherwise high in organic matter at the time, such as when corn follows alfalfa.

The Illinois test, called the ISNT test, seemed to hit a roadblock when researchers in two other states issued a report saying they could use the method to find a correlation between various soil conditions and N needs. Commercial labs can do the test, but began receiving very few requests for it after that information appeared.

Tim Smith of Cropsmith, Inc., Monticello, Ill., is a believer in the test. He had some interaction with researchers as it was being developed, and he says he now uses it successfully to help clients fine-tune nitrogen recommendations. His view is that other researchers who said it didn't work didn't include the test as part of a package of other information about the farm in making recommendations. Used correctly, he still believes it's a helpful way to know how much N to apply in various parts of the field. He's such a believer that he actually has a facility set up to process the tests.

Smith presented his views to the Top Farmer Crop Workshop at Purdue University last week. His entire company is based on making nitrogen recommendations for farmers. He uses the information he collects from the test, along with knowledge of crop rotation, soil type, planting population a d a host of other factors to make variable-rate N application recommendations.

What the test measures, indirectly, Smith says, is the soil's ability to supply nitrogen by mineralization from the soil. The plant is the final judge of how well that works or doesn't work in any given situation, but this test is simply a tool that helps Smith get a better handhold on how much N a farmer should apply in various parts of each field. It's not a test that needs to be run every year, he notes. He samples on the grid, taking a deep sample and an even deeper sample. But one tests should be good for at least five to six years, he notes.

Contact Smith at:, or call 217-621-6117. Or visit his site on the Web at:

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