COMPARISON OF ORGAN APPEARANCE AND SENESC ENCE RATES IN TALL FESCUE, COCKSFOOT AND LUCERNE (LEAVES, TILLERS AND STEMS)

Three forage species (tall fescue, cocksfoot, lucerne) were cultivated without nitrogen and water stress. Rates of leaf appearance and senes cence were compared for several regrowths (1 in spring and 2 in summer for grasses, 3 in summer and 1 in autumn for lucerne). We showed that the average phyllochrones were 83 degree-days for lucerne, 188 for co cksfoot and 253 for tall fescue and were dependent on regrowth, and al ways increased during regrowth. These intraspecific variations were in terpreted respectively by an increase in competition for light during a given regrowth and by differences in temperature according to regrow th. The maximum number of completely green leaves per tiller or stem w as a characteristic of a species (from 9 to 11 for lucerne, 3 to 4 for cocksfoot, 2 to 3 for tali fescue). However, the degree-days from lea f appearance and the beginning of senescence were less variable than t hose for phyllochrone (452 for cocksfoot, 516 for tall fescue and 705 for lucerne). For regrowths with no nitrogen and water limitations, ti ller or stem density did not increase after defoliation so that the in crease in leaf index only resulted from leaf appearance and elongation rate. These results were used to discuss the choice of a partner to a ssociate with lucerne. For grasses, we concluded that once the maximal number of green leaves was reached, there would be an increase in lam ina weight only if a lamina of given length was replaced by a longer l amina. In case of partial defoliation, the time needed to attain the m aximal number of leaves could be shorter, and the amount of senescent material greater.