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North Central Indiana | We variable rate our NH3 based on our variable rate MAP and AMS, OM, Soil type, and yield history. Kind of the same theory others have mentioned, seems the curve is similar for all soils and you just get better N efficiency from the better soils. So we variable rate based on other applied N to get our total applied between 180 and 190 pounds of actual N. Our own personal trials have shown that 200lbs of N is probably the maximum we need for max yield in a perfect year on our best soils. But the curve is pretty flat the last 10% or so which is why we landed in the range we did. There is some nuance. High O.M. Muck ground around here is 60% or greater. That ground gets no N from a “primary” N source. Just gets whatever is dry spread for P and S and our starter. We also put in a few check blocks every year, pretty easy to do with a variable rate map, to keep an eye on how a significantly higher and lower rate would do
Edited by JRCS Farms 2/1/2026 10:42
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