Forage Nutritional Characteristics of Orchardgrass and Perennial Ryegrass at Five Irrigation Levels

As water resources become limiting, the need to produce stable amounts of highly nutritional forage increases. An understanding of how levels of irrigation affect crude protein (CP), digestible neutral detergent fiber (dNDF), in vitro true digestibility (IVTD), and neutral detergent fiber (NDF) is critical in pasture forage management. Cultivars of orchardgrass ( Dactylis glomerata L.) and perennial ryegrass ( Lolium perenne L.) were established under a line‐source irrigation system to evaluate the effect of five water levels (WLs) and three harvest dates on concentrations of CP, dNDF, IVTD, and NDF. Perennial ryegrass forage had higher CP, dNDF, and IVTD and lower NDF concentrations than orchardgrass at all harvest dates and within WLs. The most notable trend in nutritional value across WLs was the near linear increase in CP ranging from 175 g kg −1 at the wettest WL to 217 g kg −1 at the driest WL. Digestible NDF ranged from 709 to 757 g kg −1 at corresponding WLs. These trends were particularly evident later in the growing season. Orchardgrass maturity (early vs. late) had little effect on forage nutritional characteristics across WLs. Combined over WLs, tetraploid perennial ryegrass cultivars averaged higher concentrations of CP, IVTD, and dNDF and lower NDF values compared with diploid cultivars. In general, as water stress increased, forage nutritional value (i.e., CP and dNDF) increased.