CANOPY DEVELOPMENT AND LIGHT-ABSORPTION OF GRAIN LEGUME SPECIES IN A SHORT-SEASON MEDITERRANEAN-TYPE ENVIRONMENT

The adaptation of a number of grain legume species is being investigat ed for fine-textured, neutral to alkaline soils that are unsuitable fo r narrow-leafed lupin production. Canopy development and light absorpt ion are important characteristics influencing crop adaptation. In shor t season, Mediterranean-type environments, crops with rapid early cano py development minimize evaporation from the bare soil and maximize tr anspiration and light absorption, leading to rapid dry matter accumula tion. In this study, the canopy development and light absorption of fa ba bean, field pea, narbon bean and chickpea were compared on a fine-t extured, neutral to alkaline soil in a dryland Mediterranean-type envi ronment at Merredin, Western Australia. The principle factors determin ing early canopy development of the above grain legumes were investiga ted. Among the species studied, high rates of leaf expansion and large leaves resulted in a high percentage of absorbed photosynthetically a ctive radiation (PAR) and rapid ground cover as measured by the sunfle ck. Faba bean had high leaf expansion rates (mean of 1.33 cm(2) d(-1)) and a large maximum leaf size (59.4 cm(2)), and hence, absorbed a lar ge percentage of PAR (77% at 74 DAS). In contrast to faba bean, the me an leaf expansion rate of chickpea was only 0.11 cm(2) d(-1), its maxi mum leaf size was 6.9 cm(2) and it absorbed 43% of the PAR by 74 DAS. The rates of leaf expansion for narbon bean and field pea were similar to that of faba bean, but their leaves were significantly smaller tha n faba bean and greater than chickpea. Both field pea and narbon bean absorbed 58% of the PAR at 74 DAS. Rates of leaf appearance did not se em to have a large influence on rate of canopy development due to comp ensation between the number of branches and leaf size. In general, spe cies with few branches developed their canopy faster than species such as chickpea, which had many branches.