Phenological Stage and Herbage Quality Relationships in Temperate Grasses and Legumes

Abstract Phenological indexes that account for variation in chemicál composition of herbage would be valuable to farmers and researchers. Hence, the objective of this study was to relate neutral detergent fiber (NDF) and in vitro digestible dry‐matter (IVDDM) concentrations in herbage and plant parts of alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), timothy (Phleum pratense L.), and smooth bromegrass (Bromus inermis Leyss.) to phenological development of each species. Four replicate plots of each species were harvested at four 2‐wk intervals during the spring of 2 yr. Alfalfa was separated into leaves (including flowers) and stems; red clover into leaflets (including flowers), petioles, and stems; and bromegrass and timothy into leaf blades and stems (including sheaths). Herbage from two plots of each species was scored for phenological stage according to a species‐specific index and a mean stage number (mean stage by weight, MSW) was calculated. For each plant part, NDF and IVDDM concentrations were regressed on MSW across years. Alfalfa leaves remained constant in NDF (206 g kg−1 dry matter, DM) and IVDDM (783 g kg−1 DM) with increasing MSW; however, MSW accounted for 97% of the variation in NDF and IVDDM concentrations of alfalfa stems and herbage. Herbage concentrations of NDF and IVDDM were more closely related to MSW than were concentrations of NDF and IVDDM in leaflets, stems, or petioles of red clover, and leaf blades and stems of bromegrass and timothy. Only in alfalfa did MSW adequately account for variation in NDF and IVDDM of herbage and plant parts. Phenological models for the other species adequately accounted for variation in some, but not all, plant parts.