Bleeding rate of field-grown maize with reference to root system development

Bleeding rate could be an effective index for the physiological activity of a whole root system in field-grown crops, because it is based on active wa ter absorption caused by root pressure. We examined the bleeding rate of fi eld-grown maize with reference to root system development. The bleeding rat e decreased rapidly just after detopping, which suggested negative effects of shoot removal on bleeding in maize. The bleeding rate of different plant s at every hour showed that it has a diurnal change pattern with the maximu m value occurring at around 8 a.m. Then we examined the bleeding rate early in the morning with reference to shoot growth. It increased with shoot gro wth and root development to reach the maximum value at around tasselling an d decreased thereafter. The number and diameter of nodal roots emerging acr opetally along the stem were increasing until tasselling. Therefore signifi cant positive correlations were evident between the bleeding rate and the r oot morphological traits, such as total number, diameter, and cross area of nodal roots of a whole root system until tasseling, although these relatio nships were not clear afterwards. Physiological activity per unit root mass was estimated on the assumption that bleeding rate is a product of root mo rphology and its physiological activity. The physiological activity per uni t root mass increased in the former half of the growing period, then decrea sed, possible because of the relative relationship between the formation of new roots and the senescense of existing roots.