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Physiological Components of Yield and Tolerance to Frequent Harvests in Alfalfa¹

Alfalfa (Medicago sativa L.) cultivars consist of genotypes that vary in herbage yield and tolerance of frequent harvests. Our objectives were to identify genotypes differing in yield and harvest tolerance and to determine whether these differences were correlated with specific physiological and biochemical differences. We established 144 alfalfa clones in field plantings (30 cm spacings) and harvested them four times the 1st year and then 7 to 8, 5, or 4 times annually for the next 2 years. On 30 October of the 3rd year, herbage, crown and root tissues of 12 selected clones were analyzed for several carbohydrate, N and P components. The high-yielding clones identified in this experiment had statistically higher concentrations of soluble carbohydrates, starch, inorganic P, and NH₄⁺ in various plant parts than did low yielding clones. Clones tolerant of frequent harvests generally had higher concentrations of nonstructural carbohydrates, starch, organic and inorganic phosphorus, and amide-N in roots and crowns than did harvest-intolerant clones. Selection criteria may be developed through a refinement of these relationships and used to identify desired alfalfa plant types with improved yield and persistence.

Key Words: Medicago sativa L. • Organic phosphates • Inorganic phosphates • Total nonstructural carbohydrates • Starch • NH₄⁺ • NO₃^– • Amide-N

² Plant physiologists and research technician, respectively, Light and Plant Growth Laboratory, Plant Physiology Inst., ARS, USDA, Beltsville, MD 20705.

³ Visiting scientist, Shikoku Agric. Exp. Stn., Agronomy Division, Zentsuji, Kagawa-Ken, Japan.

Received for publication February 5, 1977.