Forage quality of tall fescue across an irrigation gradient

Abstract

Water available for irrigating pastures in the western USA is often limited and varies widely across sites and seasons. Objectives were to determine the trends in crude protein (CP), neutral detergent fiber (NDF), and in vitro true digestibility (IVTD) of 10 cultivars of tall fescue (Festuca arundinaceae Schreb.) at five levels of irrigation and three harvest dates (early, mid-, and late season). A secondary objective was to evaluate the effect of the endophytic fungus [Neotyphodium coenophialum (Morgan-Jones & Gams) Glenn, Bacon & Hanlin] on these trends. Cultivars differed significantly for CP, NDF, and IVTD, and differences were generally consistent across water levels (WLs). Concentration of CP increased in a near linear manner (154-189 g kg-1) from the highest to lowest WL; however, total protein yield decreased from 611 to 447 kg ha-1 with less water, closely following the trend in forage yield. Forage quality at the late-season harvest, as indicated by lower NDF and higher IVTD values, was significantly higher at the lowest compared with the highest WL. Also, NDF was significantly lower and IVTD significantly higher at the late-season harvest at all WL. Presence or absence of the endophyte was not associated with CP; however, there was a tendency for the endophyte-free cultivar to have lower NDF and higher IVTD than its endophyteinfected counterpart at the higher WL. The magnitude of quality differences among the 10 cultivars indicates that forage quality should be a major consideration in the choice of cultivars for pastures of the Intermountain region.