Forage Quality of Plant Parts of Perennial Grasses and Relationship to Phenology

Abstract

Limited information exists regarding forage quality variation among plant parts of divergent genetic lines within perennial grass species and its relationship to phenology. This investigation was conducted to determine these relationships in ‘Napier’ and ‘Orion’ orchardgrass (Dactylis glomerata L.), ‘Barton’ and ‘Rebound’ smooth bromegrass (Bromus inermis Leyss.), germplasm of reed canarygrass (Phalarls arundinacea L.) selected for either high or low specific leaf weight, and germplasm of tall fescue (Festuca arundinacea Schreb.) selected for either high or low rate of leaf‐area expansion. These grasses were seeded on a Webster silty clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll). Morphological stage determined by the Simon and Park method during spring growth was closely related to accumulated growing degree days (GDD) by using a 5°C base (r2 = 0.97). Within each year, decline in herbage in vitro digestible dry matter (IVDDM) and crude protein (CP) concentration was closely related to calendar day, GDD, and morphological stage, although least to morphological stage. Thus, for morphological staging systems to more accurately predict forage quality, the proportion of reproductive and vegetative tillers in swards will need to be considered as well as their development. Larger cultivar differences in IVDDM occurred within stems of orchardgrass (24%) than within leaves (7%). In smooth bromegrass, Rebound stems were 12% more digestible than those of Barton, but Barton leaves were 6% more digestible than Rebound leaves. There were few genetic differences in CP concentration within any species and no consistent differences in IVDDM within the reed canarygrass or tall fescue germplasms. Thus, cultivar variation for IVDDM was not uniform among plant parts, and selecting grass plants on the basis of specific leaf weight or leaf‐area expansion rate seems to have little effect on forage quality.