Measurement of root diameter in field-grown crops under a microscope without washing

The variation in the root diameter of field-grown crops was directly measured under a microscope by manually removing soil particles from roots without washing the roots. The frequency of the root diameter at the mode (about 10 μm, mainly of root hairs) was higher in wheat and maize (about 60%) than in soybean and sugar beet (about 30%), and it was the lowest in potato (21%). The diameter of 88 to 97% of the roots larger than 20 μm ranged from 21 to 160 μm. The finer the roots, the higher was the frequency, except for potato roots in which the frequency of roots with a diameter of 21 to 40, 41 to 80, and 81 to 160 μm was about 30%. Since fine roots and root hairs account for the largest proportion of the crop root system, they should appropriately be quantified whenever morphological and physiological aspects of roots are analyzed.