What is the Illinois Soil N Test (ISNT)? The test was developed several years ago at the University of Illinois by researchers in the Department of Natural Resources and Environmental Sciences. It is a laboratory procedure designed to measure N liberated from soil heated for 5 hours with dilute alkali solution (sodium hydroxide). The test does not measure nitrate, but does measure exchangeable ammonium and a fraction of soil organic N. The theory behind the test is to extract a specific component of organic N from soil collected before planting and N application that can reflect the amount of N mineralized in a growing season to plant-available N forms (converted to inorganic ammonium and nitrate). The concept of estimating mineralized soil organic N is not new, as many biological and chemical methods have been proposed for the past 50 years. At best some of those tests predict available soil N in closed systems, such as in pots under greenhouse conditions, and none have been proved useful in predicting plant-available N in open systems such as field conditions. Unfortunately, it is extremely difficult to predict mineralization that might occur in the field with a lab test. This is the reason there has not been a reliable test developed or recommended to date.
Sawyer, John and Tabatabai, Ali, "The Illinois Soil N Test: Should it be used in Iowa?" (2005). Integrated Crop Management News. 2411.
The Iowa State University Digital Repository provides access to Integrated Crop Management News for historical purposes only. Users are hereby notified that the content may be inaccurate, out of date, incomplete and/or may not meet the needs and requirements of the user. Users should make their own assessment of the information and whether it is suitable for their intended purpose. For current information on integrated crop management from Iowa State University Extension and Outreach, please visit https://crops.extension.iastate.edu/.