Fig. 2 Relationship between fibrous root length in each diameter class and NUR of Kentucky bluegrass. A: very fine roots, diameter <0.064 mm; B: fine roots, diameter <0.064 to <0.2 mm; C: medium roots, diameter 0.2 to <0.5 mm; D: large roots, diameter 0.5 to <1.0 mm; E: very large roots, diameter 1.0 mm