Soybean canopy development as affected by population density and intercropping with corn: Fractal analysis in comparison with other quantitative approaches

To better understand how crops intercept light, the complexity of plant str ucture needs to be characterized. Fractal analysis provides a novel approac h for quantifying the geometric structure of individual plants. The objecti ves of this study were to determine (i) an appropriate methodology for esti mating fractal dimension (FD) two-dimensionally for complex three-dimension al structures of plants such as soybean [Glycine max (L,) Merr.]; (ii) whet her the temporal pattern of FD for soybean structure is altered by populati on density or intercropping with corn (Zea mays L.); and (iii) how the FD f or soybean structure compares with other quantitative measures of shoot dev elopment. Soybean plants were randomly sampled in monocropped soybean and i ntercropped corn-soybean plots grown at the same site in three successive y ears. Sampled plants were cut at the stem base, and leaf blades were immedi ately detached. Leafless plant structure was photographed from the side whi ch allowed maximum appearance of branches and petioles. The FD was estimate d two-dimensionally from the scanned and processed images. Fractal dimensio n of soybean leafless structure increased with time for all treatments, coi ncident with the increasing complexity of structure as shoots developed. Th e rate of linear increase of FD with time varied among treatments. Leaf are a per plant, plant height, and number of leaves per plant increased with ti me for all treatments, indicating a positive correlation with FD. In contra st, light penetration decreased during canopy development, and was negative ly correlated with FD. Whereas leaf area evaluates the surface available fo r light interception, FD characterizes its geometric distribution in space.