Evaluation of sorghum root branching using fractals

Root branching and architecture play a significant role in water and nutrient uptake, but description of these parameters has not been easy due to the difficulty of observing roots in their natural arrangement. Fractal geometry offers a novel method for studying the branching patterns of roots. Plants of ten diverse sorghum (Sorghum bicolor (L.) Moench) genotypes (five of African origin, three of US origin and two hybrids composed of African×US lines) were grown in root boxes containing 80% sand and 20% fine-textured Sharpsburg silty clay loam topsoil. The root fractal dimension (D) and abundance (log K) were determined at nine regions within the profile. Roots were washed free of growth media and photographic slides were taken of each region. Values of D and log K were determined by projecting photographs onto grids of progressively increasing sizes. The number of intersects was regressed on log grid size. Differences in D were found among genotypes (1·44[les ]D[les ]1·89) suggesting that these sorghum genotypes may be associated with greater root branching patterns. Greater fractal dimension (branching) and abundance values occurred in the 0–35 and 35–70 cm depths of the soil profile within the root box, indicating a greater root distribution in that part of the profile. Significant differences were also noted in branching patterns for sorghum genotypes derived from different sources. In general, the African sorghums were more branched and deeper rooted than the US-derived genotypes. Results indicated that fractal dimension can be used for the description of sorghum root system morphology and provides a good measure of branching patterns which can be distinguished.