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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.

Although soil moisture availability is the most limiting factor in crop production in many areas of the United States, little progress has been made in developing cultivars tolerant to moisture stress. The objective of our study was to evaluate a drought box screening procedure for use in alfalfa (Medicago sativa L.) breeding to improve performance under less than optimum moisture conditions. Seven diverse alfalfa cultivars and three germplasm sources were evaluated for forage yield and root characteristics under three moisture treatments in drought boxes in a shadehouse. Divergent selection for forage yield was practiced in the low and intermediate moisture treatments, and for high forage yield in the high moisture treatment. Selected plants were intercrossed within groups and progenies were evaluated under similar conditions. Average forage yield was reduced 30 and 55% in the intermediate and low moisture treatments, respectively, when compared to the high moisture treatment. Entries did not differ for yield in the low moisture treatment, but they varied in their yield response to increasing rates of irrigation. Variability among plants for forage yield was not reduced by moisture treatments. Root weight decreased and root fibrousness increased as moisture stress increased. Entries differed for all root characteristics measured. Forage yield was correlated with all root characteristics, but we concluded that the added information did not justify the time, labor, and expense of root excavation. Selection and evaluation in the intermediate moisture treatment resulted in the greatest progress and differentiation among populations.

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