Comparison of Five Methods for Characterizing Soybean Rooting Density and Development¹

Abstract

Many methods are used to study plant root system development and function. Most methods are tedious and time‐consuming. Some require expensive, sophisticated equipment and frequently require highly trained operators. Few studies are published where several methods are compared for their time requirements, equipment needs, soil applicability, and validity of the results. This study determined usefulness of five methods for characterizing soybean (Glycine max (L.) Merr.) rooting depth and density in a loess [fine, silty, mixed (calcareous) mesic family of Typic Udorthents] soil. The methods were: (a) soil water‐depletion, (b) framed‐monolith and pinboard, (c) core‐sampling, (d) mini‐rhizotron, and (e) trench‐profile. Each method was used or attempted on several dates during the 1975 growing season. The soil water‐depletion method was fast, required only simple equipment, and provided satisfactory estimates of rooting depth but did not provide reliable estimates of rooting density. The framed‐monolith method was very time‐consuming, but provided quantitative estimates of rooting density with depth and could have provided rooting density estimates with distance from the row. The core‐sampling method was faster than the framed‐monolith method. Cores could be obtained either with a hand‐turned bucket auger or with a coring machine, but several profiles were required to obtain rooting density distributions with depth and distance from the row. The mini‐rhizotron method was fast, but did not provide accurate results, presumably because the mini‐rhizotrons were installed too late. The trench‐profile method provided semiquantitative estimates of rooting density with depth and distance from the row. The trench‐profile method was rapid and required no time‐consuming separation of live roots from debris of previous years. The hand‐augered core, soil water‐depletion, and the trench‐profile methods could be used through the entire growing season, but the framed‐monolith and the mechanized‐core methods were not satisfactory during a drought period because the soil column collapsed during sampling.

Comparison of citrus rooting evaluation methods using root images in soil profiles and root weight

“…All these results confirm the validity of the trench wall profile method, which, besides being less troublesome than others, such as the monolith and the auger methods (Böhm et al, 1977) gives a clearer idea of the extension and distribution of the root system. It was observed from the results obtained here, that images are a very useful tool, as they make root quantification in the trench wall profile method easier.…”

“…This result is better than obtained in the present study with citrus root images, but with the digitized image system it is not necessary to count roots in the field. Böhm et al (1977) compared the monolith, auger, mini-rhizotron, trenchprofile and soil water depletion methods in soybean roots. The water depletion method provided a good estimate of the depth of the roots but was not efficient in estimating the root density by soil volume.…”

Applications of minirhizotrons to understand root function in forests and other natural ecosystems

“…Although there is evidence that both deep and shallow roots may be over-represented (Bohm et al, 1977;Gregory, 1979;Hansson and Andrrn, 1987), comparisons with soil core data more frequently reveal that shallow roots are under-sampled by minirhizotrons (e.g. Ball-Coelho et al, 1992;Bohm et al, 1977;Majdi et al, 1992;Merrill et al, 1987;Samson and Sinclair, 1994 and others cited therein). A number of explanations for this phenomenon have been offered.…”

Root water uptake and profile soil water as affected by vertical root distribution

“…Weekly investigation on roots was conducted on three randomly selected bulk field plants using a modified trench-profile method (Bohm 1976). The method has been reported to be the best among the five frequently used methods including soil auger method (Bohm 1977). The roots of the bulk field and container plants on which xylem sap flow was measured were collected along the soil profiles immediately after completion of the final observations on root water uptake.…”