Relationships between the Areas of Successive Leaves on Grain Sorghum1

Grain sorghum [Sorghum bicolor(L.) Moench] plants characteristically exhibit an increase in the areas of successively older leaves on the shoot up to a maximum value, followed thereafter by a decrease in leaf areas. Data from 2 yr of field studies were used to develop empirical functions relating average areas of successive leaves. These functions were representative for a number of published data sets and exhibited the following characteristics: (i) an early exponential phase of leaf area increase apparently terminated by the onset of intraplant competition; (ii) a transition between two linear phases of leaf area increase that appears to be invariant among years, cultivars, and treatments; and (iii) a final phase of decreasing leaf areas that is apparently sensitive to interplant competition and reproductive growth. Data from the literature and studies involving water stress, plant population, and N fertilizer application effects indicate that, while reproductive organ growth may affect some aspects of leaf area development, the onset and severity of intraplant and interplant competition may be more important factors determining individual leaf areas.