"Alfalfa uses all 13 nutrients like all other crops," said Craig Peterson, Federated agronomist at the Ogilvie location, "but [alfalfa] has a high demand for phosphorus (P) and potassium (K).

That translates into 12-14 lbs. of P and 26-32 lbs. of K removed from the soil for every ton of dry matter alfalfa, according to Peterson, which is equal to 26-32 lbs. of DAP and 83-116 lbs. of potash -- and that's a depletion that will affect the crop yield in subsequent seasons.

Fertilization is critical. As is a soil test.

"A high testing soil will help with part of the nutrient needs . . . a low test may fix or tie up some of a fertilization application, [but] having a current soil test is a must to achieve a healthy, high-yielding stand," said Peterson.

Fertilizer options vary based on soil test results.

• Alfalfa can be very responsive to sulfur, especially in lighter textured soils. Using a sulfur product that breaks down slowly can be beneficial to help prevent leaching. "Elemental sulfur is a good choice," said Peterson, because it will help keep sulfur in the soil profile longer.
• Alfalfa sometimes benefits from ammonium sulfate (AMS) when a more instant response is needed. Peterson said, "A blend of elemental sulfur and AMS may fit better for longer season needs."
• Potash is ideally applied after both first and third cuttings; a "late winter or early spring application can damage the crowns of the alfalfa plants," he said. Potash applied right after the third crop helps build winter hardiness. Peterson noted that for dairy rations, if all the potash goes on alfalfa in one application, it can affect the levels of K in feed, and nutritional adjustments need to be made. 

Be sure to talk to your Federated Agronomist with any questions about fertilizing alfalfa, or if you would like soil testing assistance.