Light interception, photosynthetic activity, and crop growth rate in canopies of six temperate forage grasses.
Growth rates of grasses in midsummer at complete light interception were 21.9 g/m2 day (3.9% light energy conversion) for timothy cv. S352, 25 g (4.3%) for cocksfoot cv. S345, 28.9 g (5.2%) for timothy cv. S48, 36.4 g (6.5%) for Phleum bertolonii cv. S50, 40.5 g (7.3%) for cocksfoot cv. S37 and 43.6 g (7.8%) for tall fescue cv. S170. A high crop growth rate was associated with erect leaves and a low extinction coefficient for visible radiation, but there were no significant differences between the varieties in individual leaf photosynthesis. Three types of simulation model, those of Verhagen et al. [HbA 34, 878], Monteith [HbA 35, 1392] and de Wit [HbA 36, 357] all gave predictions of crop photosynthesis of the right order of magnitude, but further information on respiration of the crop was necessary in order to assess how far they could predict varietal differences in crop growth rate.