The influence of time of tiller origin and nitrogen level on the floral initiation and ear emergence of four pasture grasses

Abstract

Summary A study was undertaken for perennial ryegrass, Italian ryegrass, cocksfoot, and timothy, of the floral initiation, ear emergence, leaf number at ear emergence, and percentage of fertile tillers with dates of origin between May 1958 and February 1959. The influence of two levels of nitrogen was examined. Despite large ranges in their time of origin, winter and earlyspring tillers of perennial ryegrass, Italian ryegrass, and timothy all initiated floral primordia within a relatively short period. Ear emergence followed the same pattern. Mean leaf number at ear emergence decreased with tillers of later origin to minima of 6 for perennial ryegrass, 7 for Italian ryegrass, 9 for cocksfoot, and I+ for timothy. In cocksfoot and timothy the percentage of fertile tillers was high only for those formed before mid winter, whereas in perennial ryegrass and Italian ryegrass the percentage remained high even for tillers formed up to late spring. High nitrogen promoted earlier floral initiation and ear emergence, and a greater percentage of fertile tillers. The effect was most marked in cocksfoot. The majority of heads emerged during the 3–4 week period after the first recorded ear emergence in each species. The heading of perennial ryegrass was inhibited by a controlled high day/night temperature of 90°F/70°F over a 7-week period.