https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1833-2020.pdf
Among the potentials for enhancing production, profitability, and nutrition efficiencies of alfalfa crops is through effective use of fertilizers. For many soils in the low desert of Arizona, phosphorus (P) as a phosphate fertilizer is very commonly applied prior to planting alfalfa. Potassium (K) is assumed to be abundantly available in desert soils; therefore, not typically applied to crops. Nitrogen (N) fertilizer is generally not applied for alfalfa production since alfalfa can obtain its own N from N-fixing nodules. Specific information about the interactions and effects of P and K on alfalfa yield and quality for Arizona has not been developed. This publication by Ayman Mostafa and Worku Burayu of the University of Arizona Cooperative Extension Field Crops Program investigated and demonstrated the importance of balanced fertilizer applications to maximize alfalfa yield. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1833-2020.pdf