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A Method to Separate Plant Roots From Soil
and Analyze Root Surface Area
J.G. Benjamin
PROBLEM: To study the effects of soil management
practices on plant growth we need to investigate the effects of the soil
environment on root growth. Studying soil management effects on plant root
systems often is deterred by cost, in terms of time and labor, for collecting
root samples, for washing the soil sample and for separating the live roots from
previous years’ roots and other organic debris. Methods that speed the process
of washing soil from roots and that enable the researcher to quantify the amount
of roots washed from a sample without the need to separate the roots from other
organic materials in the sample, allow many more samples to be collected and
processed for study.
APPROACH: We constructed a root washer for samples up to
4 inches in diameter and 9 inches long. As many as 24 samples can be washed at a
time in about 1 ½ hours. We developed a method to determine the surface area of
the roots from the sample without the need to manually separate the roots from
soil debris. The washed samples are placed in a tray on a flat-bed scanner. The
digital scan is accessed by a commercially-available image analysis software
where the projected area of roots in the sample is manually measured. The
projected area is then transformed into total root surface area.
RESULTS: Root area estimates from soil samples were
accurate when a small enough grid size for the image analysis software was used.
For this procedure, a grid density of 2 mm or less between lines was the most
accurate, with a slope of the correlation line nearly 1 and an r2 of
0.98. Removing debris from the sample was necessary only if the samples were
very dirty. If the debris in the sample was greater than 20% of the projected
area, measurement accuracy suffered due to occlusion of the plant root fragments
by other materials. Partitioning of the sample into more than one scanning tray
could be necessary to allow accurate measurements of the root materials in very
dirty samples. Sample processing time was reduced from 20 hours per sample for
hand separation of roots from debris to about 0.5 hour per sample when analyzing
the image from an uncleaned sample.
FUTURE PLANS: We are using this technique to analyze root
samples taken from studies on water use and productivity by legumes suitable for
the semi-arid west. The speed of washing and measurement of root distributions
allows more samples to be processed with the time and personnel available and
will allow enough samples to be processed to decrease experimental error in
statistical analysis.
The author may be reached via e-mail:
J.G. Benjamin
or phone: 970-345-2259.
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