Relationship Between Tillering and Forage Yield of Tall Fescue. II. Pattern of Tillering

Several reports suggest that cool-season grasses produce few tillers in midsummer, but few studies have been conducted to simultaneously measure rates of tiller initiation and tiller death. To evaluate the role of tillering in yield differences among tall rescue (Festuca arundinacea Schreb.) genotypes, live and dead tillers were counted weekly during the growing season. Genotypes were selected for low (LYT), medium (MYT), and high yleld/tiller (HYT), and in plant studies they exhibited a high, medium, and low rate of tillerlng, respectively. A mathematical technique was developed to estimate equilibrium tiller density, i.e., the density where appearance of new tillers occurred at the same rate as other tillers died. Three separate field experiments were established by vegetatively propagating the genotypes and allowing them to develop into sward-llke conditions. In two experiments cutting heights of 5 and 10 cm above-ground level were compared, and in one experiment, plants of birdsfoot trefoil (Lotus corniculatus L.) were grown in mixture with the genotypes to evaluate genetic effects on competitive ability of the grass component. Plants were harvested four times and remained in a vegetative condition throughout the growing season. Live tiller density increased until early summer after which it decreased and then increased again in fall. Decline in summer was due to an increased death rate as well as a decreased initiation rate. The LYT genotype had the highest rate of tillering and developed the highest tiller density at equilibrium, about 31, 35 and 44 vegetative tillers/dm² for Exp. I, II, and III, respectively, whereas the HYT genotype maintained the lowest density of about 16, 16, and 30 vegetative tillers/dm², respectively. The MYT genotype was intermediate in all experiments. Death rate of tillers was also highest in the LYT genotype and lowest in the HYT genotype. Cutting height had little effect on tillering pattern or density. The reasons why the HYT and MYT genotypes did not reach the same tiller density as the LYT genotype are unclear.