Root growth in seedlings of annual pasture species

Summary The mean rate at which roots of 12 annual pasture species penetrated a yellow sand to a depth of 80 to 90 cm varied from 0.8 to 3.2 cm per day.Penetration rate was closely correlated with seed weight until roots reached a depth of about 20 cm. Thereafter rates became progressively less dependent on seed size.Penetration rate varied with time. In six species a minimum rate was reached at a depth of 18 to 24 cm. In two species rhythmic fluctuations in root penetration rate appeared to be associated with the development of new leaves on the shoot.Shading the shoots substantially reduced root penetration rate but the rhythmic fluctuations persisted. These observations are consistent with the hypothesis that the rate of root penetration is determined by the supply of metabolites to the root system.