Leaf dynamics of timothy and meadow fescue under Nordic conditions

Leaf production dynamics of timothy (Phleum pratense L. cv. Tarmo) and meadow fescue (Festuca pratensis Huds. cv. Kalevi) were studied in Finland under field conditions in mixed swards containing timothy, meadow fescue and red clover (Trifolium pratense L. cv. Björn) harvested by cutting. Fifteen randomly selected tillers of both species were marked and leaf number, leaf appearance rate (LAR), leaf elongation rate (LER), leaf senescence rate (LSR) and leaf live span (LLS) were followed through weekly observations. Concurrently another set of fifteen tillers of each species was dissected on each occasion to determine the number of unemerged leaves and development stage of the apex. The first observation period was between 26 April and 22 June and the second between 22 July and 22 September.The species differed clearly for most of the measured parameters but most differences were dependent on the season. In spring, timothy started growth earlier, had higher LAR (+57%), produced more leaves (+83%) with higher LERgross (+58%), higher LSR (+61%), higher LERnet (+54%) and produced larger tillers (+193% in leaf area) than meadow fescue. In autumn, timothy still had a higher LAR (+80%), produced more leaves (+60%) with higher LERgross (+36%), but had also a higher LSR (+77%) and thus similar LERnet (0%) to meadow fescue. Timothy tillers were only slightly larger than meadow fescue tillers (+20% in leaf area). The consequences of these findings on competition in mixed swards and implications for grazing theories are discussed.