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Selection for Increased Phosphorus in Alfalfa and Effects on Other Characteristics¹

Phosphorus is an essential element in both plant and animal nutrition. However, in some alkaline soils alfalfa (Medicago sativa L.) does not always respond to P fertilization despite deficient or low P concentrations in the tissues. Objectives of this study were to determine the feasibility of selection for increased P concentration in alfalfa grown in alkaline soils and effects on nontarget forage yield and quality characteristics. Ten diverse unselected alfalfa populations, and first and second cycle selected populations were evaluated for P and Ca concentration, Ca:P ratio, and forage yield. selected populations were also evaluated for forage yield, nontarget minerals, and forage quality characteristics. Unselected populations differed in P concentration, but variability among individual plants was considerably greater than among populations. Selection on the basis of P concentration of individual plants was effective with 7 to 12% increases over the check in Cycle 1 and an additional gain of 6% with a second cycle of selection. Realized heritabilities with individual plant phenotypic selection were 0.17 and 0.36 in the first and second cycles of selection, respectively. Selection for increased P concentration did not affect Ca concentration, but reduced the Ca:P ratio and increased Zn concentration. No detrimental effects of selection for increased P concentration were found for nontarget minerals, components of forage quality, or yield. Selected populations did not differ from the check population in response to P fertilization. Selection among individual alfalfa plants from any genetic source based on P concentration in forage from the first harvest would be the most efficient breeding procedure to increase P concentration.

Key Words: Medicago sativa L. • Mineral concentration • Heritability • Breeding procedures • Forage quality

² Former graduate assistant, former graduate assistant, professor, assistant professor, and associate professor, respectively, Dep. of Crop and Soil Sciences, New mexico State Univ., Las Cruces, NM 88003.

Received for publication January 21, 1986.