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A Comparison of Three Methods for Estimating Root Length¹

The root system from a 10-week-old soybean plant was washed free of soil and total root length estimated by three different techniques. Direct measurements were first made on fresh root samples and later, from projected black and white photograph transparencies of the fresh material, further estimates of root length were obtained by two additional methods. The first of these was the opisometer method which, in essence, requires tracing over the entire length of root in the sample. The second method, developed by Newman, requires counting of the number of intersections between the randomly diffused roots and a grid line of known length.

The coefficient of variation for means of three estimates by each method showed that there was little difference in precision between methods. However, with Newman's method, an estimate was made in 1.0 hour compared with 5.0 hours for the direct method and 1.5 hours for the opisometer method.

Key Words: Roots

² Research Assistant, Agronomy Department, University of Illinois; Research Soil Scientist, USDA, and Associate Professor of Soil Physics, Agronomy Department, University of Illinois; and Research Soil Scientist, USDA, and Professor of Soil Physics, Agronomy Department, University of Illinois, Urbana; respectively. The technical assistance of Roger Blair and Omar Giraldo in this work is gratefully acknowledged.

Received for publication July 30, 1969.