Factors Affecting Rate of Leaf Emergence in Barley and Wheat

Abstract

Rate of leaf emergence of wheat ( Triticum aestivurn L.) and barley ( Hordeum vulgare L.) changes with sowing date and temperature and appears to be set early in the plant's life cycle. Four models that advance different hypotheses to explain this variation are examined. None is completely satisfactory, partly because of a nonlinear response to thermal or photothermal time. Soil strength, N nutrition, and depth of sowing affect rate of leaf emergence, as may sub‐zero temperature or ontogeny. An alternative hypothesis proposes that leaf emergence rate depends on daylength and acclimation to temperature. Potential rate of leaf emergence may be determined by factors acting on leaf primordia, which are initiated early in the life cycle.