Application of a straight N fertilizer, such as urea or ammonium nitrate, is usually unnecessary. Yes, alfalfa requires large amounts of potassium and it should be applied as fertilizer when a soil test indicates a deficiency. Potassium deficiency in alfalfa is almost as common in Oklahoma as phosphate deficiency and the need for liming. Normally, elements other than P and K are abundant in Oklahoma soils and only rarely need to be added as fertilizer. Potassium availability in soils is closely related to annual rainfall.
Current evidence shows that potassium deficiencies for alfalfa are common throughout Oklahoma.
The only way to know about the need for potassium fertilizer is to have a soil test. Calcium, magnesium, and sulfur are used in large amounts by alfalfa. Availability of calcium and magnesium are closely linked to soil pH, as the soil becomes acidic and needs to be limed, these elements approach deficiency levels. Liming acid soils replenishes both available calcium and magnesium to adequate levels. Sulfur moves with water in the soil, so when alfalfa extracts water from deep in the soil, sulfur is also extracted.