Larry Wikoff
Soil Scientist/CPSS

AGVISE Laboratories has reported on the Amino Sugar-N test in the last two issues of our newsletter. We now offer this test to interested customers. For a quick review, the test was developed after reports that corn did not always respond to N fertilizer on fields where Illinois researchers thought it should. This prompted the researchers at the University of Illinois, lead by Mulvaney, to successfully identify the fraction of organic nitrogen that mineralizes readily. (i.e. easily converts from organic-N to plant available N forms). The readily available form of organic nitrogen they found was Amino Sugar-N. Their studies showed that fields with a high level of Amino Sugar-N did not respond to N fertilizer and fields with a low level of Amino Sugar-N did respond to applied N.

As we stated in previous articles, while the Amino Sugar-N test looks like a promising way to identify sites that will not respond to N fertilizer, much more correlation work has to be done to make the test reliable under a range of conditions. The original U of Illinois data indicated that sites with an Amino Sugar-N level above 240 ppm did not respond to N fertilizer. Unfortunately in the real world things are not always so black and white. The 2001 trials showed a similar response, but a few of the fields that had Amino Sugar-N tests over 240 ppm responded to applied N when they shouldn't have. Illinois researchers are not sure why the test failed on a few sites in 2001 and they are still trying to figure it out. But that's the real world "Baby, Yeah". The data from the 2002 field studies shows an almost perfect relationship (see figure). The fields that tested over 240 ppm did not respond to N fertilizer. For now, the University of Illinois is wondering why a few fields in 2001 were out of whack. This will take more investigation and more field trials.

The Amino Sugar-N test looks like a "good" test to identify sites that will not respond to nitrogen if used in conjunction with other field information on factors that affect N status of soil such as manure history, soil temperatures, and moisture status. It is also important to test the nitrate level on these fields, because we know if the nitrate level is high initially, there will be limited response to applied N. More research is needed to identify when this test will be reliable, and under what conditions it may fail.

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