Allometric relationships in field-grown soybean

Allometric relationships in plants uncover size-correlated variations in form and development and characterize the relative growth of a part of a plant in comparison with a whole. Stable allometric relationships in ontogeny can be used as components of crop models and to estimate plant parameters that are difficult to measure. Our objective was to discover whether stable allometric relations exist in ontogeny of field-grown soybeans (Glycine max L.). We used field data on vegetative stages, plant height, stem weight, and leaf weight of 16 soybean cultivars measured on farms and on the experiment station of Mississippi Stale University during 1993-1995 growing seasons. The number of observed crops for each cultivar ranged from one to 14. Stem heights displayed linear log-log dependencies on the vegetative stage, before and after the breakpoint stage, which typically was between the 'fourth node' and 'sixth node' vegetative stages. Slopes of the log-log dependencies after the breakpoint stage were similar in all cultivars. Stem mass had log-log linear dependencies on stem height. Slopes of these dependencies differed among cultivars grown under the same conditions, and among crops of the same cultivar grown under different conditions. Water stress could be a modifier of these relationships. The proportion of leaf weights in the total weight of leaves and stems decreased linearly as the vegetative development progressed. Since allometric relations are stable for a specific crop, they can be used to forecast vegetative development as soon as they are established. (C) 1998 Annals of Botany Company.