The information presented here is applicable to alfalfa grown throughout Idaho and east of the Cascade mountain range in Oregon and Washington. Different climates, soils, and topography result in considerable variation in alfalfa yields across a region, an individual farm, and even within a field on the same farm. Due to this inherent variability, a one-size-fits-all recommendation for the management of any one nutrient is of little value. Nutrient management choices should be based on individual grower practices, realistic yield expectations, and current soil and tissue test information.
This document summarizes locally-based guidelines for managing major nutrients in alfalfa, emphasizes how producers can tailor recommendations to their production system, and identifies opportunities where information such as soil and tissue test results can help
Nutrient removal by alfalfa
Growing alfalfa removes large quantities of nutrients from soil (Table 1). In fact, high- yielding stands of alfalfa hay remove as much or more nutrients than any other intensive forage managed for hay or silage. Growers have historically relied on phosphorus and potassium as the main nutrients added for optimal alfalfa production. Areas with a long history of alfalfa and other intensive crops have commonly mined soil nutrient reserves. This, coupled with modern, higher-yielding varieties and production systems, means that many alfalfa fields now require supplementation with multiple nutrients.
Soil pH and alfalfa
Optimum alfalfa yields occur when soil pH is near 7.0; however, alfalfa can tolerate soil in the pH range 6.0–8.2 and still produce high yields. Northern Idaho and western Oregon and Washington, where rainfall is high, have lower soil pH than more arid regions of the inland