Biomass Partitioning, Forage Nutritive Value, and Yield of Contrasting Genotypes of Timothy

Abstract

Forage nutritive value and dry matter (DM) yield are negatively related. Hence, the improvement of both DM yield and nutritive value requires the identification of genotypes that deviate from that negative relationship. Our objectives were to evaluate the potential of simultaneously selecting for high forage yield and high nutritive value in timothy (Phleum pratense L.), and to study the relationship between DM yield, nutritive value, and biomass partitioning. Nine genotypes, and a reference cultivar, Champ, were studied in a growth room, with limiting and nonlimiting N rates. At both N rates, some genotypes differed significantly in forage (FDM) and total biomass (TBDM) DM yield, leaf weight ratio (LWR), and root weight ratio, but did not differ in forage (FNC) and total biomass (TBNC) N concentration. Genotypes differed in neutral detergent fiber concentration, in vitro true digestibility, and in vitro cell wall digestibility under limiting N only. Significant interaction (P < 0.05) was found between genotype and N rate for DM yield and for most of the other measured parameters. Principal component analysis indicated that, for most genotypes, the differences in FDM resulted from differences in TBDM and not only from changes in biomass partitioning between shoots and roots. Also, variability in the relationship between FDM and LWR indicated the possibility of selecting genotypes having high yield with high LWR. Consequently, it is possible to break the linkage between high DM yield and declining nutritive value parameters and select for high‐ yielding genotypes with superior forage nutritive value.