“The surface layer of many of these fields has an acid pH. This acid layer often is only a couple inches deep, but it can be severe enough to reduce the ability of alfalfa roots to absorb nutrients from the soil.”
More importantly, the acid can prevent nodules from forming on the alfalfa roots, and seedlings will be unable to produce their own nitrogen.
To head off problems, Anderson advises gathering two types of soil samples before planting – one at a normal 7-8” depth and one only 2” deep. “Then have the lab analyze the normal sample with the usual tests for phosphorus, potassium, pH, and so forth, but just test the shallow sample for pH.”
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