Alfalfa/grass response to nitrogen and phosphorus applications

Abstract

Alfalfa/grass (Medicago sativa/Dactylis glomerata, Bromus) yield and quality responses to nitrogen (N) and phosphorus (P) fertilizer applications are well documented. The magnitude of the P response and in turn N, may however, be limited by the relative immobility of P in the soil. A two‐year field study was conducted to determine the response of an established alfalfa/grass stand to combinations of a one‐time broadcast application of N, P, and sulfur (S) rates with fall or spring applications of P. Nitrogen and P applications increased forage production, nutrient concentration and nutrient content, particularly in the first production year. No S response was observed. Fall P applications were superior to spring applications only in the first year of production. If annual broadcast applications of P are made to existing alfalfa/grass stands in Intermountain areas, fall applications are recommended.