Potassium and Phosphorus for Quality Alfalfa

Adequate nutrition all season long is a vital component of high-yield, high-quality forage production. Alfalfa specialists suggest building phosphorus (P) and potassium (K) soil fertility levels to high and liming acidic soils to pH 6.5 to 7.0 prior to the establishment process. Then the alfalfa stand will require special attention to fertility maintenance, frequency of harvest, use of crop protection chemicals, and other practices, for years of high-level production.

Dr. Mike Stewart of the Potash & Phosphate Institute (PPI) www.ppi-ppic.org/agri-briefs points out key facts regarding nutrition as it affects not only the alfalfa crop but also the performance of animals receiving alfalfa in their diets.¹ He reports that:

• Alfalfa requires a continuous supply of nutrients during the season. Each ton of hay removes approximately 15 pounds phosphorus pentoxide (P₂O₅), 60 pounds potassium oxide (K₂O), 5 pounds sulfur (S) and 5 pounds magnesium (Mg). Being a legume, alfalfa can provide for its own N (about 55 pounds per ton). A properly limed soil supplies calcium (Ca) and most other nutrients. Alfalfa often responds to boron (B) applied with maintenance fertilizer.

• Phosphorus can be used effectively by alfalfa when broadcast with maintenance K and B applications. Phosphorus is involved with energy storage and transfer, vigorous root development, hastened maturity, nodule formation and nitrogen fixation, and other essential functions in the plant.

• Potassium is essential for stand longevity. It’s key to rapid regrowth rate, nitrogen fixation, photosynthesis, efficient water use within plants, suppression of invasive weeds and grass, improved winter hardiness, as well as high levels of key animal feed ingredients such as protein, TDN, and others.

Ruminant animals require high levels of K, since it’s essential for sustaining rumen microorganisms and maintaining the animals’ water and feed intake. High- performance, lactating dairy cows have particularly high dietary K needs. The K is essential not only to produce large quantities of milk but also to help animals better tolerate stress induced by high temperature.

¹Agri-Briefs, Spring 2006, No. 6.

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