kg Ϫ1 , using short-season dormant or semidormant cultivars with reported annual DM yields of alfalfa that Potassium fertilization rates for alfalfa (Medicago sativa L.) have ranged generally between 10 and 15 Mg ha Ϫ1 in three been increasing with intensive cropping systems or decreasing with policies that generally lead to reduced fertilizer inputs. In this case, to four harvests per season (Markus and Battle, 1965; nutrient buildup or maintenance of high soil test levels may not be Lutz, 1973; Smith, 1975; Rominger et al., 1976; Fixen desirable and drawdown of K reserves may be beneficial in the short and Ludwick, 1983; Barbarick, 1985; Alva et al., 1986; term. The objective of this research was to evaluate the effects of Sheaffer et al., 1986; Burmester et al., 1991; Razmjoo potassium fertilization of alfalfa in areas of high soil exchangeable K and Henderlong, 1997). The reported results of these levels and long growing seasons. A field experiment was established trials show that the effects to the applications of K varied under irrigation from 1993 to 1997 in the Mediterranean environment with production practices, growing conditions, and soil of the Ebro Valley (Spain) on a silty clay loam soil. The treatments K contents, ranging from no DM yield response with were five annual rates of K (0, 41.5, 83, 166, and 332 kg K ha Ϫ1 ) and the application of 300 kg K ha Ϫ1 with a soil test level two rates of K (166 and 332 kg K ha Ϫ1 ) applied prior to seeding on of 75 mg K kg Ϫ1 (Lutz, 1973) to a maximum response two alfalfa cultivars. The average annual dry matter (DM) yield was 21.5 Mg ha Ϫ1 and showed a small linear response to K fertilization with the application 448 kg K ha Ϫ1 for a soil with extract-(Pr Ͼ F ϭ 0.0589). Total K removal in the herbage increased linearly able K of 55 mg K kg Ϫ1 (Rominger et al., 1976). These with each rate of K and reached 1728 kg K ha Ϫ1 with the application studies show that in general, K application increased of 332 kg K ha Ϫ1 yr Ϫ1 , compared with 1546 kg K ha Ϫ1 without K plant and soil K concentrations. fertilization. At the end of the experiment, soil ammonium acetateAlthough a survey of soil fertility and forage manageextractable K (K e ) increased little with K rates, and the differences ment specialists indicates that additional K is rarely were observed only in the first 30 cm of depth. Despite the uptake recommended when the concentration of exchangeable of 1546 kg K ha Ϫ1 , soil K e values did not change appreciably, suggesting K is greater than 300 kg ha Ϫ1 (about 150 mg K kg Ϫ1 ) in that much of the K uptake was derived from the fertilizer and from
