Production and physiological responses of Italian ryegrass and white clover grown in monocultures and mixed stands

Ryegrass and clover, when grown under optimal conditions in mixed stands interact in response to available light energy. With other resources non-limiting, pasture production is determined by the efficiency with which solar radiation is intercepted by canopies and converted into dry matter. The aim of this study was to investigate the nature of these interactive responses in terms of morphological and physiological mechanisms. Pasture canopy structure and growth were studied under a four-weekly clipping treatment. The ability of the mixed canopy to intercept photosynthetically active radiation (PAR) was investigated and compared to the individual pasture components. In addition, utilization of intercepted light was quantified. Light use efficiency (C02 fixed per unit absorbed PAR) as well as photochemical efficiency of photosystem II (FvFm–1 were studied. The results indicate that the interactive responses between ryegrass and clover in mixtures resulted in increased production as well as increased light interception abilities. Morphological characteristics (i.e. canopy structure) of the various components wasfound to be of major importance in determining light interception ability. There were no significant differences amongst the various treatments in their ability to utilize intercepted PAR for CO2 assimilation. However, slight increases in the ability of photosystem II to utilize assimilated CO2 during photosynthesis were present in monocultures compared to mixed stands. These physiological differences did not have an effect on production potential of the mixed stands. African Journal of Range & Forage Science 17(1, 2&3): 101-11