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Last update on .

This is the first of a multipart series on how to make site-specific, nitrogen rate recommendations using the SoilDx FertiSaver-N system.

Key takeaways
  • Measuring the organic N fraction of soil is a useful approach to determine soil N availability.
  • The Illinois Soil Nitrogen Test is a simple chemical test to measure the amino sugar N fraction in organic matter.
  • The results of the test need to be interpreted in a context dependent manner: It is not sufficient to look for simple thresholds in the ISNT value to make nitrogen rate predictions. Other factors such as soil type, depth, available water, and soil pH are critical to accurate recommendations
  • The ISNT has been evaluated independently by several groups and on several crops beyond corn in the Midwest.

Last update on .

The nitrogen cycle, simplified
The nitrogen cycle, simplified

Q: Why are some soils more fertile than others?

Dr. Khan:

Most soils of the Midwestern USA are very fertile because they are moderate to high in organic matter, developed on deep loess deposits and have good nutrient and water supplying potential. These soils need less nutrient inputs from fertilizers, as opposed to those soils that are lower in organic matter with a limited rooting depth, and thus lower in overall nutrient supplying capacity.

Last update on .

Q: How is nitrogen gas (N2) converted to plant-available nitrogen?

Dr. Khan:

The ultimate source of all nitrogen used by plants is N2 gas, which accounts for 78% of air. In order for plants to use it, N2 must first be converted to ammonium (NH4+) through biological or chemical fixation.