Stability of forage yield of alfalfa clones grown with five associate species

Abstract

Single species spaced-plant clonal nurseries are useful in the first stage of selection to develop forage crop cultivars for semiarid and arid environment pastures. The objectives of this study were (1) to quantify the degree of stability of forage yield of individual alfalfa (Medicago sativa L.) clones when grown with five associate species and (2) to examine the relationships of alfalfa and the associate species in the determination of total plot forage yield in a spaced-plant nursery with a stand density comparable to that of natural plant communities on semiarid rangelands. One hundred plants of NC-83-1 alfalfa were vegetatively propagated and grown in a replicated spaced-plant selection nursery in association with Fairway crested wheatgrass (Agropyron cristatum [L.] Gaertner s. lat.), Oahe intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth & D. R. Dewey), RS-2 hybrid wheatgrass (Elytrigia repens [L.] Nevski × Pseudoroegneria spicata [Pursh]Löve), Vinall Russian wildrye (Psathyrostachys juncea [Fisch.] Nevski), and NC-83-1 alfalfa. Plants were spaced 0.5-m apart on a rectangular grid in which eight plants of an associated species surrounded each alfalfa plant. Forage yield per plant was measured in four harvests each year during the 2nd and 3rd years following establishment. Alfalfa was the most competitive associated species. Rhizomatous grasses were more competitive to alfalfa than were bunchgrasses. Some clones were phenotypically more stable than others. The degree of stability was inversely, but weakly, associated with the amount of alfalfa forage produced. Alfalfa plant yield was negatively related to yield of the associate species. This compensatory effect tended to stabilize total plot forage yield. Simultaneous selection of range forage species may best be accomplished in nurseries in which a grass and a legume are interplanted at a density and in a pattern that simulates the competitive relations occurring in semiarid environments. Key words: Competition, grass, Medicago, plant breeding, pasture, range