Two grasses and two legumes were grown at three illuminances: one grass and one legume in a growth cabinet (100, 50 and 34% relative illuminance) and one of each in a glasshouse (100, 30 and 10% relative illuminance). The response to shading was investigated by using classical growth analysis techniques, and the photosynthesis-respiration balance obtained by Watson and Hayashi's method. Shading caused a reduction in the proportion of root and a corresponding increase in the proportion of leaf, and an increase in the shoot/root ratio in all species except green panic. The relative growth rates of grasses (which were only clearly superior at the highest illuminance) were affected more by shading than were those of legumes, and the greater shading effect resulted from a greater decrease in net assimilation rate, and to a lesser extent, from a smaller compensatory increase in leaf area ratio in the grasses than in the legumes. The greater sensitivity of net assimilation rate of grasses to shading arose from a stronger dependence of the photosynthetic rate on illuminance. The significance of these findings for pasture production is discussed. Both tiller and runner production were dependent upon the total amount of radiant energy received by the plant, and in the growth cabinet, at least, were independent of its intensity, duration and sequence. ______________________ *Part IV, Aust. J. Agric. Res., 25: 415 (1974).

Inclined point quadrat analysis was applied to pure swards of two pasture species, Desmodium intortum and Setaria sphacelata. Canopy structures are described in terms of the denseness and inclination of foliage and stems. Light penetration patterns throughout the day were calculated. The two species differed greatly in these characteristics. Desmodium leaf was oriented at a uniform mean angle to the horizontal throughout the height of the canopy, but leaf occurred predominantly in the upper layers. In contrast, leaf angles in Setaria varied down the profile, with most of the leaf in the middle layers. There were diurnal variations between and within the species in the amounts and distribution of sunlit leaf area index.Diurnal patterns of canopy photosynthesis were estimated from calculated leaf and light profiles, photosynthesis-illuminance data, and records of incident radiation. There was an overall 1.8 : 1.0 advantage in sward photosynthesis by Setaria, arising from a greater than two-fold superiority at high angles of the sun, falling to a 1.6 : 1 .0 advantage at low angles. This trend follows the diurnal patterns of light penetration into the two canopies. From calculated sward photosynthesis, concurrently measured dry matter production, and other data it was concluded that the relative magnitude of productivity corresponded very closely to the relative photosynthetic capacities of the leaves. Therefore, canopy structures were comparatively unimportant as determinants of yield differences. ________________ *Part II, Aust. J. Agric. Res., 21: 183 (1970)

The growth analysis technique for the separation of photosynthetic and respiratory components of net assimilation rate used in previous controlled environment studies of early vegetative growth was extended to natural lighting conditions. The use of short-wave radiation rather than days in the light as the quantification of photosynthetic opportunity in the regression analysis improved the accuracy of estimation of photosynthesis and respiration. In one experiment, concurrently with the growth analysis procedure, carbon dioxide exchange measurements were made on one grass and one legume. There was good agreement between the two methods in the estimates obtained. The data support conclusions from previous experiments concerning the superior growth rate of grasses. Species rankings were similar in both sets of experiments. ____________________ *Part III, Aust. J. Agric. Res., 22: 865 (1971).