Effect of root-zone temperatures on morphology, growth and development, yield, and yield components of annual medics

Annual medic pastures are an effective component of ley-farming systems (cereal-legume rotations) in Australian areas with a Mediterranean climate, but they have been unsuccessful in areas near the Mediterranean Sea. In some zones with a Mediterranean climate, like Iran and Syria, root-zone temperature is considered the major growth-limiting factor for annual medic early in the growing season. In order to study the effect of low root-zone temperature (RZT) on growth and development, yield, and yield components of some annual Medicago species, an experiment was conducted in a controlled-environment chamber. In this experiment, 3 species of annual medics, namely Medicago polymorpha, M. radiata, and M. rigidula, thought to be adapted to cold and temperate conditions, were used. Four root-zone temperatures (5, 10, 15, and 20degreesC) were considered. The experimental layout was a completely randomised block design with 4 replications. There were differences among the annual medics for dry matter and yield components. Two species, M. polymorpha and M. rigidula, had more leaf, stem, and root dry matter, plant height, leaf and stem to root ratio, leaf to stem ratio, and leaf area and yield than M. radiata. Therefore, M. polymorpha and M. rigidula may be better suited for ley-farming systems in cold and temperate zones. The results also showed that the 5degreesC RZT effectively decreased the yield and yield components of the annual medics. In conclusion, application of ley-farming is not likely to be successful when RZT is below 5degreesC, especially during vegetative development. Therefore, in the zones where soil temperature is greater than 10degreesC, annual medics have normal growth and produce average yields. Ley-farming (cereal-legume rotation) could be replaced with fallow-cereal rotation.