Systematic Approach To Delineate Management Zones From Nitrate Sampling Using NDVI Maps.

Today more farmers are starting to side-dress nitrogen. It can be very cost effective to use a starter fertilizer and/or summer application of nitrogen. With the high cost of fertilizer and varying soil yield potential, it has become obvious that some form of variable rate Nitrogen application will maximize yield efficiency. Some farmers are already doing a type of variable rate application, but deep nitrate sampling in season would take the guess work out of the process. Farmers are currently using old grid sample soil tests or field yield maps for this purpose, but with a low-cost deep nitrate soil test from Solum Inc, one doesn’t need to guess how much to apply. The deep nitrate sample tests were done with a Solum® nitrate testing machine in Hayfield Minnesota. The data used to conclude if NDVI (Normalized Difference Vegetation Index) maps could delineate management zones came from 10 acre nitrate grid samples from a few select fields from 7,583 acres sampled. To test the accuracy of the nitrate sampling machine and the mixing process, a field test was performed using a composite sample from soil we mixed from two different spots in the field. The accuracy of this test should help with making a decision on the overall amount of nitrogen to add to get the maximum yield. Solum® nitrate testing results can be obtained in twenty-four hours or less. The only way to make the test cost effective is to use 10acre grids, but this presents an issue of having no nitrogen management zone boundaries to follow. Thats why in-season NDVI was overlaid with the Nitrate results to help delineate lines to better manage the different zones of the field. Some years there’s more nitrogen from the previous years than others. Denitrification and leaching can vary from year to year. Taking a deep nitrate sample and using other precision agriculture tools will help manage nitrogen more efficiently, because it will be looking at the current year with current results.