Competitive ability of tall fescue against alfalfa as a function of summer dormancy, endophyte infection and soil moisture availability

Authors: MALINOWSKI, D - Texas Agrilife; BUTLER, T - Samuel Roberts Noble Foundation, Inc; Belesky, David

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2010
Publication Date: 5/1/2011
Citation: Malinowski, D.P., Butler, T.J., Belesky, D.P. 2011. Competitive ability of tall fescue against alfalfa as a function of summer dormancy, endophyte infection and soil moisture availability. Crop Science. 51(3):1282-1290.

Interpretive Summary: Changing trends in long-term weather patterns challenge traditional pasture production strategies. New forage plant resources and management strategies are needed to provide production system resilience when confronted with changing short- and long-term weather patterns. One plant adaptation strategy is to avoid active growth in the presence of inhospitable growing conditions. Plants with this capability are likely to be summer dormant plants that would persist in hot, dry environments by avoiding exposure to excessive heat and drought, while remaining productive in the cooler portions of the year. Combinations of forage plants are needed to sustain herbage production in pastures during stressful intervals and to buffer variation in productivity associated with time and growing conditions. One benefit of growing summer-dormant plants with legumes is natural introduction of the important plant nutrient, nitrogen that stimulates herbage production and augments herbage nutritive value. We found that summer-dormant cultivars of tall fescue were not vigorous competitors when grown with alfalfa but that summer-active tall fescue was able to compete with alfalfa in a mixture of the two species. It appears that currently available summer-dormant tall fescue cultivars are not viable.

Technical Abstract: Summer-dormant cool-season grasses might be a viable component of pasture if Mediterranean and Mediterranean-type environments with relative mild winters and hot and dry summers. Management practices for summer-dormant forages are being developed, including production strategies with compatible legume species. Summer-dormant (Flecha and TX06V) and summer-active (PDF) cultivars of tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] that were either noninfected (E–) or infected (E+) with native or novel endophytes were grown alone or with alfalfa (Medicago sativa L.) cv. Bulldog. Field and greenhouse experiments were carried out with controlled or naturally-occurring intervals of soil water deficit. Indices of competitive interactions (relative yield, RY; relative yield total, RYT; and aggressivity, AGR) were calculated. Summer-dormant tall fescue had RY < 0.50, while summer-active PDF had RY values similar to those of alfalfa (RY = 0.50). Endophyte infection increased RY of TX06V by 34%. RYT values for all tall fescue – alfalfa mixtures were not different from RYT = 1, but were less for Flecha-alfalfa mixtures under soil moisture deficit. Endophyte effects on RYT were not consistent. Alfalfa had greater AGR than summer-dormant, but similar to summer-active tall fescue. Results suggest that tall fescue with incomplete dormancy (Flecha) may not tolerate a summer-active competitor (alfalfa) during summer. Cultivars with high degree of dormancy (TX06V) may be less affected by competition from alfalfa, but may not be as competitive as summer-active tall fescue.