ABSTRACT
Root architecture is another important plant morphological char acter that deserves special consideration relative to physiological aspects of crop yield, because roots in many instances control devel opment of the entire plant. Root architecture refers to the spatial con figuration of root systems, including length, diameter, and hairs. Root architecture is very complex and dynamic in nature. It is related to plant species and cultivars within species, and can be modified by en vironmental factors (Eghball et al., 1993; Costa et al., 2002). Root systems play a major role in controlling plant growth and develop ment due to their importance in absorption of water and nutrients (Barley, 1970; Lynch, 1995). Availability of nutrients in the soil is de termined not only by chemical, physical, and biological factors, but can also be actively influenced by plant roots. A nutrient element has to move to the root and/or be contacted directly by the root surface to be absorbed. For the relatively immobile nutrient such as P, most of the micronutrients, and to some extent K, the amount of roots pro duced (root surface area) by the plant become a controlling factor in determination of total uptake of these nutrients. Root systems gener ally contact only very small fractions (1 to 2 percent) of the soil vol ume. Therefore, the effectiveness of plant roots in absorbing immo bile nutrients will be influenced markedly by the extensiveness of root systems, the capacity of a unit root length to absorb contacted nutrients from soil solution, and changes that occur in growth rates and nutrient uptake efficiency of roots as plants grow (Adepetu and Akapa, 1977). Further, roots provide mechanical support to plants from seedling through maturity and development. In addition to their function in water and nutrient absorption and mechanical support, roots are important in N chemistry whereby it can be transported to
shoots through the xylem, either as inorganic N or as amino acids and amides. Roots can also synthesize growth substances and hormones such as cytokinins that may be important in leaf function and possibly grain development (Evans and Wardlaw, 1976).
