Today I sat down to work on variable rate fertilizer maps and I stumbled onto a field that pronounces the importance of variable rate fertilizer and zone soil testing. I ran into a few things that everyone should be aware of. This is happening in almost all of the fields that I help producers manage. This particular field is an MZB full systems field and has pulled some rather large crops in the past. We sampled like a normal practice. The soil tests look as follows.

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I would like you to look at two columns into that interest me: the N6 and the P-Ols.  I explain first what you are looking at and why the importance.  The N6 column represents the nitrogen carryover in the 0-6 inch depth and the P-Ols column represents the parts per million of phosphorus.  The nitrogen carryover allows producers to use the credit from the unused nitrogen in the soil for the next years crop. Phosphorus tests that are under 8 ppm can significantly reduce yield.  I like to build phosphorus test to 12 ppm and then manage those fields. Significant yield responses are tied directly to phosphorus levels for all crops in this area.  With all that said I get to my point, soil tests are extremely variable and therefore the amounts of fertilizer that need to be applied to those areas is variable.  MZB breaks down a field into like areas in a field and those areas are called zones.  Those zones are then soil tested separately from one another and managed separately. 

(Click the image to enlarge)

Above I attached at zone map of the field.  The different zones are denoted by the different colors.  The acres in each zone are on the right side of the zone map.  The different zones match up to colors as follows: Zone 1- Red, Zone 3- Yellow, Zone 5- Gold, Zone 8- Royal Blue, Zone 9- Bluegrey, Zone 11- Light Green, and Zone 12- Dark Green. 

Below I attached the recommendation of the same field.  Notice how the amounts of actual urea and phosphorus applied vary in this field.  Roughly 73% of the field is not receiving any phosphorus.  Urea application rates vary from 151 pounds to 354 pounds.  Now take this into consideration a normal application of this field prior to MZB would have been 400# of 36-16-0.  Even if you do not believe that you can raise a better crop in those zones that need more fertilizer products; you surely should see a cost savings where you don’t need the extra product.  I just showed you the fertilizer differences seed prescriptions are equally as beneficial. 

In closing, we put 400# of 36-16-0 prior to MZB on this field on every acre.  This year we averaged on this field 404 pounds of total fertilizer per acre, so we virtually applied the same amount of fertilizer per acre.  It was applied to the acres the needed the fertilizer and could grow more bushels rather than blanket rating the whole field.  The facts are in the numbers- 73.5% of this field would have been over applied and 26.5% was under applied.