Where In The World Did That Information Come From?

Social Media, podcasts, and radio are great ways to share agronomic ideas and knowledge over a wide geography, however the listener needs to keep in mind that the information can be geographically biased, and how bias that can impact how applicable the information being shared is to your business.

Recently one of our clients was listening to a program that noted that, “any quality soil lab should perform a nitrate nitrogen test as part of a basic routine test.” The client had called to inquire why the S1 basic soil test package at ALGL does not include a nitrate nitrogen test.

If the client was collecting soil samples from an arid region of the US, such as the western parts of Kansas, Oklahoma, Nebraska, or the Dakotas, Montana, or Western Canada, it would be advisable to add nitrate to a routine soil test to measure residual nitrate at the end of the season. If the winter months provide a large portion of the annual rainfall in the region where the sample was collected, but annual rainfall totals still falls under 10-20 inches, it may be best to hold off till spring to test for the residual soil nitrogen. Either way nitrate soil tests in these regions can indicate significant nitrogen levels in the soil available for the next growing crop, especially where the drought conditions during the 2021 growing season reduced soil water and crop growth.

Annual Mean Total Precipitation - NOAA 2021

Source: NOAA, 2021

Now compare that to the central and eastern portions of the corn belt. As you move east the annual rainfall increases by a factor of 4 to 7. This creates extended time periods of soil moisture leading to quicker conversion of ammonium nitrogen sources to nitrate. It also increased the frequency of saturated soil conditions leading to denitrification and loss, as well as increased leaching of nitrate down through the soil profile. All of these factors increase the chance of nitrogen loss from the crop root zone.

In these eastern regions any residual nitrogen from the growing season reflected in fall soil samples is usually lost though the winter, or taken up by a cover crop. Either way the nitrogen is not present in a traditional 6-8” soil sample used in the region.  A fall soil nitrate test may show some excess nitrate in the soil, however the nitrogen most likely will not make it through the winter to the next growing season. Unless a manure is applied, a spring soil nitrogen test will usually only reflect low native soil levels, normally less than 10 ppm. Spring nitrate nitrogen tests commonly range from 4 to 7 ppm, representing less than 15 - 30 pounds of applied N. Regardless of the lab location, the statement is only applicable to samples collected in the western portion of the US and Canada.

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