The Illinois Soil Nitrogen Test (ISNT) is a new soil test available to New York corn growers. Developed by University of Illinois researchers, the ISNT estimates the level of readily mineralizable soil organic N and is an accurate tool for determining if additional N is needed for a corn crop.
The ISNT has been adapted and calibrated for use in New York, thanks to the work of Quirine Ketterings of the Nutrient Management Spear Program, Cornell University, graduate students Jon Klapwyk and Joe Lawrence, and many others.
I know what you’re thinking: “too busy to take soil samples, precise timing, 12-inch cores, bad time of year” and all the negative things related to the Pre-Sidedress Nitrate Test (PSNT). Take a deep breath: New York-specific research shows that the ISNT can replace the PSNT and all the headaches that come with it. The ISNT comes with sampling guidelines favorably different from the PSNT. Let’s take a look.
• The ISNT soil sample may be pulled at any time of the year, keeping one guideline in mind: It cannot be taken within five weeks of adding manure, of sod or cover crop plowdown or of chemical kill. Why? When organic sources decompose, ammonium-N is formed first, followed by the conversion of ammonium to nitrate.
The ISNT picks up the ammonium-N in the soil in addition to soil N from soil organic matter. This gives an inaccurate reading of soil organic N in times when ammonium levels are elevated. Sampling at any other time, when soil conditions are suitable, will yield an analysis that predicts organic N supply for up to three years. You learn if your soil has enough readily mineralizable soil organic N to not need additional fertilizer N.
• The ISNT requires a 6- to 8-inch soil core – not the 12-inch core required for PSNT – taken randomly across your field.
• Follow the same procedure you use for a standard analysis package. The ISNT test can be done as a standalone sample or be added to the standard soil analysis provided by the Cornell Nutrient Analysis Laboratory, killing two birds with one stone.
New York research shows that no sidedress N is needed in first-year corn following sod, therefore, there’s no need to sample first-year corn after grass or legume sods. Sampling one time and getting the standard results in addition to the ISNT is a convenient option. Remember: The standard soil analysis comes with three years of nutrient recommendations based on your crop rotation and allows you to spread soil sampling across several years.
A response curve based on New York research reflects the ISNT result versus Loss-on-Ignition (LOI), which is a measure of total soil organic matter. If your soil falls below the curve, you’re likely to see a response to sidedress N. You should follow N guidelines for that soil and crop year after subtracting any starter, manures, compost or rotation contributions.
The ISNT is a convenient and economical tool to balance your corn crop’s total N need with homegrown N and commercial sources. Escalating commercial N prices puts an even greater value on homegrown N. Find out what you are working with.

Know more…
Mike Dennis answered this month’s question. If you have questions or want soil test kits, contact him in the Seneca County office, where he handles small farm and agronomic issues for Seneca County Cooperative Extension. Tel: 315-539-9251. Email: mgd3@cornell.edu
Or contact your local Extension office.
This website has a fact sheet on the Illinois Soil Nitrogen Test, as well as other information on corn production: http://nmsp.css.cornell.edu/publications/factsheets/factsheet36.pdf
Contact your local Extension office for copies of any of these documents.
For information about the Cornell Nutrient Analysis Laboratory, see its website: http://cnal.cals.cornell.edu/

Have a question? Ask Extension. The Northwest New York Dairy, Livestock and Field Crops Team is ready to answer your tough production, management and general farming questions. Send your questions to Cathy Wallace via email: cfw6@cornell.edu
Tel: 585-343-3040. Ext. 138. Fax: 585-343-1275
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