Larry Wikoff
Soil Scientist/CPSS

The search for a soil test that can estimate how much "N" will be mineralized each year has been underway for more than a century. Mineralization is the formation of inorganic-N through the microbial decomposition of organic matter and crop residue. The process transforms organic nitrogen into ammonium (NH4+) and eventually NO3- nitrogen, which is available for plant uptake. Predicting nitrogen fertilizer needs in areas like the Great Plains is fairly accurate when the nitrate test is used, but it could be better. There is good correlation between the nitrate test and crop response due to lower risk of nitrogen losses in low rainfall areas. However, in higher rainfall areas like the Midwest, the fall nitrate test is less reliable due to higher risk of nitrogen losses through the winter. Alternative methods which use preplant and pre-sidedress testing of soil nitrate have met with limited success. These areas need a test which will help determine the amount of nitrogen which will be mineralized during the growing season and contribute to crop growth and yield.

Recent research at the University of Illinois provides renewed hope for a soil nitrogen test that could work in higher rainfall areas, not suited to fall nitrate testing. In fact this new test may provide extra information when used along with the soil nitrate test to help us make more accurate nitrogen fertilizer guidelines. Researchers feel they have identified a particular form of soil organic N that mineralizes readily (becomes available quickly) and reduces the need for additional N fertilizer. This form of nitrogen is not picked up in the nitrate soil test. They feel the amino sugars are the key and they have developed a method that determines how much of these amino sugars are in the soil. This amino sugar "N" mineralization test method has been developed at the University of Illinois. Preliminary results indicate the test shows promise in predicting sites where corn will not respond to nitrogen fertilizer. Using this amino sugar "N" mineralization test, along with the soil nitrate test, may help everyone from the Great Plains to the Cornbelt make better nitrogen recommendations in the future. Additional research in the U.S. and Canada over the next few years will tell us if this new test will fit for our region.

AGVISE Laboratories has taken a preliminary look at the amino sugar-N mineralization test. Table 1 shows amino sugar-N levels and nitrates for a zone-sampled potato field in fall 2000.

Research from Illinois indicates that an amino sugar-N level higher than 225 ppm identifies sites that do not respond to additional nitrogen fertilizer in corn production. The amino sugar-N in zone 6, the old farm site, is above this level (235 ppm). The grower has known for years that he doesn't get a response to nitrogen fertilizer on this zone and has reduced N application dramatically. The nitrate test on zone 6 of 43 lb/a (0-24"), is a very normal nitrate level, but the amino sugar "N" test would have indicated that zone would not respond to additional nitrogen fertilizer.

AGVISE Laboratories is actively pursuing the development of this and other mineralization tests. The main objective is to provide growers a more accurate assessment of how much nitrogen to apply for next year's crop. We think that the soil nitrate test (0-24") used with a "N" mineralization test may enable us to provide more accurate nitrogen fertilizer guidelines in low and high rainfall areas. To fully evaluate the application of the amino sugar-N test Agvise is cooperating and exchanging samples with University and commercial labs in both the United States and Canada. We will keep you posted on new developments.

2117