|Fourteen years ago corn growers asked David
Reinart if he could pull a tissue or soil sample from their corn fields to
determine if their corn had sufficient N to finish the crop.
David pulled soil and tissue samples from about 8 of their fields, had tests run, but the results really didn't mean
much to him or the growers. The
next year, David did 20 fields and entered them on a spreadsheet where he
could compare results between fields. From this, David determined when the
best times were to pull samples that would be most cost effective.
|The next year, David had 29 fields and gathered other field data besides
the lab results. These included variety, amounts of N used, and most
importantly, the yields. After adding this field data to the spreadsheet,
things started to fall together as to what kind of levels were needed in a
field and that nitrogen application systems that before were thought to be
expensive were actually the most efficient.
|These first years, besides the lab tests for NO3 and NH4 in the soil,
and TN%, NO3 ppm, P%, and S% from tissue, David tried a brix test for
sugar and a chlorophyll meter test. The last
two tests have been discontinued because the information from them was
inaccurate or didn't correlate with what we were trying to do.
|In 1998, the program had grown to the point where it was not manageable
on a spreadsheet, so the data was entered into a database. At that
time, we also started gathering more field information including
soil types, GPM/acre, and more specifics on how N was
applied, including amounts applied thru the pivot before and after
pollination. Also we used standard fertilizer costs to compare N costs
between fields. We also calculated pounds of N/bu and % N efficiency.
|Keep in mind that during this development period not all growers would
use the N recommendations, which was fine because it allowed for
observation of different application rates, timing and types of
applications. We have seen all different kinds of systems using
large amounts of pre plant N to stingy amounts thru the pivot. Many more fields are over fertilized than under fertilized when it
comes to nitrogen.
|From studying the data we have gathered over many years, we now have the
information we need to make the best N recommendations. We try to
manage NO3 and NH4 levels during the growing season to obtain an optimum
NH4 uptake. We also now sample for K% on the tissue samples. We have found that this helps grow healthier corn with
good yields, while being very "N efficient" and environmentally
|Click here to see our sampling steps throughout
the year or here to see supporting data.