Tracing Technique

A high-quality, four- or five-head VCR is required. Frames of the root picture strip are frozen and traced on a sheet of clear plastic in sequence. Root length of each 10-cm interval is obtained by tracing roots on the clear plastic using a map measurer.

Root length can be converted to RLD using the equation

where Lr is the root length, C the magnification factor, A the area of tube observed, and D the distance from the outside surface of the tube that can be observed in soil (usually assumed to be 0.2 or 0.3 cm in the literature) (Fahey et al., 1999).

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