A New Nitrogen Test That Works
Ellen Phillips, Crop Systems Educator, Countryside Extension
Center, 708-352-0109, email@example.com
For years soil scientists have been saying that there is no good
soil test for nitrogen to use as a basis for nitrogen fertilizer
recommendations. That may be changing with the promise of a new
test being developed at the University of Illinois that can estimate
The rule of thumb for nitrogen application has been 1.2 pounds
for every expected bushel of corn yield. From there farmers would
subtract out the credits for legume nitrogen and manure in order
to come up with the final rate of nitrogen to apply to their field.
The 1.2 pound rate is based on field studies where increasing
amounts of nitrogen fertilizer is incorporated and is compared
to the yield. The most economical rate of nitrogen was recommended.
At best, this rate method is a "best estimate" guess
for a particular field in Illinois since it is not based on local
soils or conditions. Applying too little nitrogen can result in
significant yield loss. In other environments, this method might
lead to applying too much nitrogen and result in environmental
Using a standard Mason jar, University of Illinois researchers
are testing a new simple chemical test that can help farmers fine
tune nitrogen applications. It is based on measuring a material
in the cell wall of soil microbes called amino sugar nitrogen.
This sugar is just one source of soil organic nitrogen.
It is a simple test that is now being refined to make it easy
for soil labs to conduct. A soil sample is taken similarly to
present soil sampling methods. In the lab, the soil is placed
in a Mason jar with sodium hydroxide. By the lid is a container
with boric acid indicator solution. The jar is then heated for
five hours at 120 F. During this time the amino sugar nitrogen
is converted to ammonia gas that is then trapped in the boric
acid. Upon completion of the five hours, the indicator solution
is titrated and the amount of nitrogen can be calculated.
According to Dr. Rich Mulvaney, University of Illinois Crop Science
Dept., more field research is needed. Questions still being studied
are: should we sample every year, how many samples are needed
per acre, what is the right sampling depth, how should samples
be handled prior to arriving at the lab, what affect does weather
have on amino acids in soils and many more. It is believed that
this test will be able to detect fields where no nitrogen is needed
if normal climate conditions occur.
A recent study looking at 25 Illinois soils (012 inch samples)
correctly identified fields as being responsive (< 225 mg kg-1)
or nonresponsive (> 235 mg kg-1) to N fertilization for corn
production. Another study currently underway indicates that manure
applied years ago can still be providing substantial nitrogen
to a crop.
It will be a couple of years before this test is available to
soil test labs. In the mean time, current research is indicating
that this test could reduce the amount of fertilizer applied to
fields and hopefully improve the environment by minimizing excess
nitrogen being applied.