Root Elongation in the Preemergence Stage of Mediterranean Grasses and Legumes1

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Rooting depth of seedlings at emergence was determined by radioisotope tracing (P32) for six range plants: Agropyron desertorum (Fisch.) Schult; Avena sterilis L.; Medicago hispida Gaertn.; Oryzopsis holciiormis (M. B.) Hack.; Phalaris tuberosa L.; and Vicia dasycarpa Ten.; with wheat and barley as controls.Seeds were planted from 2 to 18 cm deep in loess soil in a growth chamber at 20 C constant temperature. Except for the 2‐cm depth no interaction was found between root length and depth of planting. Seedling roots reached a certain length and no more before onset of photosynthesis. This length varied greatly with the species: 4 to 6 cm for the perennial grasses anl legumes; 6 to 8 cm for Avena; and 12 cm in wheat and barley. Root length was generally correlated with mean seed weight.The depth seedling roots have reached by the time of emergence is a sum of depth of planting and root length. The deepest root penetration occurred at the greatest planting depth from which seedlings emerge. Shallow planting may be suboptimal under arid conditions, and the deepest planting form which emergence is still satisfactory seems to be optimal. Root elongation in the preemergence stage may therefore become a useful criterion in breeding species for arid range.