There are many ideas and methods available today about creating variable rate Nitrogen rates. Agronomic Solutions has worked with several methods and uses a few in particular to create VRN prescriptions. One of these is utilizing historical yield data to determine high yielding versus low yielding areas in a field and combining that data with organic matter readings. Another method is using soil types and CSR ratings to assign rates that correspond to productivity zones within a field.
There are many modeling software programs available now to determine the exact amount of nitrogen needed at any given time based on historical climate data and soil type factors. While these provide an estimate of what may be needed we still believe a soil sample taken at the 12 inch depth right ahead of sidedressing is the most accurate way to calculate a sidedress rate. We sample for nitrate on a grid basis, usually either a 4.4 or 10 acre grid. The way in which we collect the cores is very methodical as to represent soil across individual row space and several rows as we travel across a field. We strive to sample as close to sidedressing time as possible (early June) and can get nitrate results back from the lab in a short amount of time. If variable rate sidedress application is available a recommendation can be created. This is a cost effective Nitrogen program that not only uses actual lab results and georeferenced points but can be adjusted based on current/upcoming weather conditions.
The end of season stalk nitrate test is based on the nitrate content of an 8 inch section of stalk cut from 6-14 inches above the soil surface. The sample is taken after blacklayer maturity. Test results indicate how much nitrogen was available to the plant.