Semiautomated X-y-plotter-based Method for Measuring Root Lengths

Root-length measurements are an important aspect of many agronomic research programs. Several automated systems have been reported which use modifications of the line-intersect technique to estimate root length; however, most of these systems are very costly. This paper describes an inexpensive automated system using a modified line-intersect technique to estimate root length. An X-Y plotter was used to move a light sensor in a grid pattern through the projected photographic image of a root system, recording intersections with an event counter. Compared to manual counting using the Line-intersect technique, the system described accurately estimated root length of samples up to 10 m in length (r2 = 0.98). The advantage of our system is that costs are reduced by using equipment that is readily available at most laboratories: X-Y plotter and slide projector. The cost of additional items was less than $600. Each determination of root length required 50 sec. The accuracy of the system was comparable to others that are based on the line-intersect technique. Additional index words: Newman technique, Line-intersect method. R OOT-LENGTH measurements are required for agronomic investigations varying from descriptive work on depth and distribution of roots to work involving the measurement of water and nutrient uptake. All aspects of root studies are costly in terms of capital, labor, and time. The technique for estimating root length described by Newman (1966) has been used by several researchers (Rowse and Phillips, 1974; Arkin et al., 19773; Richards et al., 1979; Voorhees et al., 1980). All of these techniques use a modification of the Newman technique suggested by Marsh (1971) and tested by Tennant (1975). The Newman technique is based on the premise that length of a root system (any set of curved lines) is directly proportional to the number of intersections (N) between the root system and a random direction straight line and surface area (A) of the container confining the root system, and inversely proportional to the total length of straight ' Contribution from USDA, ARS, in cooperation with the Nebraska Agric. Exp. Stn., Lincoln, NE. Published with the approval of the Director as Paper No. 6805, Journal Series, Nebraska Agric. Exp. Stn. Received 10 Feb. 1982. Plant physiologist, USDA, ARS; professor, Dep. of Agronomy, Univ. of Nebraska-Lincoln, Lincoln, NE 68583; and agronomist, Vistron Corp., 3 Henson Place, Champaign, IL 61820 (former graduate student, (University of Nebraska-Lincoln, Lincoln, NE). 3Arkin, G. F., R. Chaison, and W. R. Jordon. 1977. Using your desktop calculator to estimate root length. Agron. Abstr. p. 79. lines (H) used to determine the intersections: a NA Root length = 2H The modification suggested by Marsh (1971) and tested by Rowse and Phillips (1974) and Tennant (1975) indicated that, if the random direction straight lines are replaced with a set of parallel lines distance D apart, the area (A) in Eq. [ l ] would be represented by HD. Substituting into Eq. [ l ] a N D Root length = --2 They also suggested that, if D was set equal to 2/a, the number of intersections would be a direct measure of root length in units of D. If two perpendicular sets of parallel lines are used (a grid system), Eq. [2] would become a N D Root length = 4 and D would set equal to 4/a. Several researchers have reported the development of apparatus to automate the Newman (1966 line-intersect method of estimating length of root systems (Rowse and Phillips, 1974; Richards et al., 1979) and projected images of root systems (Arkin et al., 19773; Voorhees et al., 1980). These authors, as well as Tennant (1975) and Reicosky et al. (1970), reported data indicating that similar degrees of accuracy could be achieved with automated modifications of the line-intersect technique as with manual measurements, with considerable time savings with the automated systems. This report describes an X-Y-plotter-based, semiautomated system for measuring root length from projected images of washed root systems that is considerably less expensive than those described in previous reports. Materials and Methods