Stability and yield of cool-season pasture grass species grown at five irrigation levels

The yield stability of cool-season pasture grasses at different irrigation levels has not been well documented. Objectives were to evaluate selection of pasture grass species in environments where irrigation may be limited or unreliable. Dry matter yield was determined for eight grass species during 1996 through 1998 at five irrigation levels. Shukla's stability statistics were calculated and species selection based on mean-yield versus Kang's yield-stability indices were compared. Tall fescue (Festuca arundinacea Schreb.), meadow brome (Bromus riparius Rehm.), and orchardgrass (Dactylis glomerata L.) had higher than average dry matter yield and were selected on a mean-yield basis. On the basis of Shukla's statistics, meadow brome and orchardgrass did not contribute to the genotype X irrigation level interaction or the genotype X irrigation level X year interaction, respectively. Perennial ryegrass (Lolium perenne L.) also did not contribute to these genotype X environment interactions; however, Shukla's statistics suggested that the linear effect of irrigation was the underlying determinant of perennial ryegrass's apparent stability. Species selection based on yield-stability indices vi ere generally in close agreement to selection of species on a mean-yield basis. One exception, Kang's Modified Rank Sum method, placed too much emphasis on stability resulting in selection of species with low forage yields. Tall fescue had superior forage yield at all irrigation levels and was always selected by yield-stability indices. Orchardgrass and meadow brome were also selected by all yield-stability indices. These results indicate that tall fescue, orchardgrass, and meadow brome are the species of choice where irrigation may be limited.