Several researchers have recognized that the rate of leaf area development during the early stages of plant growth is an important determinant of yield. This study explores differences in leaf area development among cultivars differing in maturities and discusses the relationship between vegetative growth habits and yield. Nine commercial cultivars and a breeding line were grown at a density of 10 plants per meter. The vegetative growth habits of the cultivars were monitored by periodic sampling of plant height, number of main stem nodes, stem dry weight, leaf dry weight, and leaf area index (LAI). From this information the vegetative dry weight and the maximum assimilation period (MAP) were calculated. Yield and reproductive weight was estimated by the weight of green and open bolls.

The literature indicates that, maximum canopy light interception in cotton occurs when the crop canopy reaches a LAI of 2.9. Maximum light interception is maintained until (because of leaf senescence) LAI falls below 3.1. Furthermore, canopy photosynthesis measurements have indicated that maximum assimilation rates occur with LAI values higher than 3.0. it is therefore logical to assume that the longer LAI is maintained above 3.0, the higher the seasonal photosynthate production. The period of time in which cultivars maintained a LAI above 3.0 is referred here as the maximum assimilation period.

The data indicated that full-season cultivars reach a LAI of 3.0 earlier than early-maturing cultivars, and are able to maintain LAI above 3.0 for longer periods of time. This results in longer MAP. The length of the MAP was significantly correlated with vegetative, reproductive and total plant dry weight (r = 0.65, 0.79 and 0.74, respectively, P = 0.05). The study suggests that higher lint yield may be obtained by the agronomic management of the duration of the MAP.