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Parameters of the Fibrous Root System of Sugar Beet (Beta vulgaris L.)¹

The dry weight of fibrous roots produced by sugar beets (Beta vulgaris L.) grown in vermiculite irrigated with nutrient solution was estimated by measurement of CO² evolved during wet combustion. This method gave good agreement with data obtained from direct dry weight determination on fibrous roots grown in solution culture. At 69 days postemergence dry weight of fibrous roots was 6.7 g plant^-1 in either system. There was no difference in the frequency distribution of root diameters between the two cultures, and the modal root diameter was 0.2 mm. By assuming that the frequency distribution of lengths in each diameter class was the same as the frequency distribution of diameters, the surface area was estimated to be 6.48 cm² m^-1 of length in both systems. The length-to-weight ratio of fibrous roots was a linear function of the reciprocal of their diameter, and the mean length-to-weight ratios were 286 m g^-1 in vermiculite and 275 m g^-1 in solution culture. More than 99% of the total length, but only 72% of the weight, was in roots less than 1 mm in diameter. The maximum weight of fibrous roots observed was 14 g plant^-1.

Key Words: Wet combustion • Root length-to-weight ratio • Root diameter frequency distribution • Methods of rood study

² Assistant Professor, Department of Agronomy, Cornell University, Ithaca, N.Y. 14850; Professor of Agronomy, University of California, Davis; and Plant Physiologist, Department of Soils and Plant Nutrition, University of California, Berkeley. The support of the National Science Foundation (Grant GB 14581) is gratefully acknowledged.

Received for publication July 15, 1971.