If you’re seeding new alfalfa this spring into ground that’s been in row crops for the past several years, consider getting a “special” soil test before planting, says Bruce Anderson, forage specialist with the University of Nebraska.
While seedlings in new alfalfa fields usually emerge well, they can sometimes grow slowly and often look yellow, he says.
“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.”
If the pH of the 2” sample is below 6.2, lime is needed. “But if the pH of the normal sample is above 6.2 and more than a half point higher than the shallow sample, you need only about half the usually recommended amount (of lime) because your subsoil contains much less harmful acid.”
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