Photosynthesis, Water Relations, Temperature and Canopy Structure as Factors Influencing the Growth of Sainfoin (Onobrychis viciifolia Scop.) and Lucerne (Medicago sativa L.)

Measurements of the growth of sainfoin and lucerne were madein the field after cutting on 31 May 1977. Sainfoin reacheda total above-ground dry weight of 408 g m^–2 over thegrowing period of 48 days compared with 598 g m^–2 in lucerne.Final leaf area indices (LAIs) were 2.8 in sainfoin and 6.1in lucerne. The specific leaf areas (SLAs) for sainfoin wereapproximately half those of lucerne throughout the regrowthperiod. The maximum rates of leaf appearance were 0.12 leavesper day in sainfoin and 0.85 leaves per day in lucerne. Themaximum mean rate of plant extension growth for lucerne of 2.12mm h^–1 occurred during the night, whereas, in sainfointhe maximum rate of 1.72 mm h^–1 occurred during the day. Measurements of extinction coefficients for PAR ranged from0.45 to 0.89 in sainfoin and from 0 42 to 0.57 in lucerne. Asthe lucerne crop increased in size leaf water potentials andsolute potentials became more negative. In sainfoin leaf waterpotentials remained remarkably high throughout the growth period,solute potentials decreased and turgor potentials increased.The stomatal conductances of the two species were similar. The photosynthetic capacities and rates of dark respirationper unit leaf area in both species were similar. The rate ofcanopy ‘gross’ photosynthesis at 295 W m^–2was always greater in lucerne than in sainfoin. This was largelya matter of differences between the species in LAI, althoughat higher LAIs the more erect structure of lucerne leads toa better utilization of photosynthetically active radiation. Onobrychis vicifolia Scop, sainfoin, Medicago sativa L., lucerne, photosynthesis, water relations, temperature, canopy structure