Evaluation of Video Image Analysis and Line‐Intercept Methods for Measuring Root Systems of Alfalfa and Ryegrass

Abstract

AbstractImproved quantification of plant root systems is essential for determining the functional efficiencies of plant roots. The objective of this study was to evaluate the video image analysis procedure of quantifying roots of different species and compare it with more traditional measurements. Three methods were used to quantify roots of alfalfa (Medicago sativa L.) and perennial ryegrass (Lolium perenne L.) from a greenhouse experiment: (i) root length by video image analysis, (ii) root length by the line‐intercept method, and (iii) dry root weight. Estimates of root length by image analysis and line‐intercept methods were comparable for alfalfa and were positively correlated with root weight. In contrast, the correlation between image analysis and line‐intercept estimates of ryegrass root length was poor (r2 = 0.090), and no significant relationship was found between ryegrass root length and root weight. Difficulty in the quantification of ryegrass roots was related to the large numbers of very fine roots, which resulted in extremely large root lengths and excessive error. Root data of ryegrass (and species with similar root morphology) obtained by the line‐intercept method may provide only relative values to be compared among these species. The image analysis method of root measurement is bound to improve root data with increased magnification and resolution of the video images when the root density in the image (cm cm−2) is sufficiently low.