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Nine 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 sample 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. 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, chlorophyll meter test, and an organic matter lab test. The last three 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 planting dates, 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 # 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 7 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 have found that this helps grow healthier corn with good yields, while being very "N efficient" and environmentally friendly. Click here to see our sampling steps throughout the year or here to see supporting data. |
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