March 3, 2004
The Texas Cooperative Extension
Soil, Water and Forage Testing Laboratory does thousands of
plant analyses a year at $15 each, and many are unnecessary,
said the Extension soil chemist and director of the lab.
Soil tests, when the sample is properly collected, is nearly
always a more accurate tool and sufficient in diagnosing most
commercial production and home landscape problems. Soil testing
should always precede tissue analysis, said Dr. Tony Provin, and
one of the featured speakers at the Annual East Texas Fruit &
Vegetable Conference, held here Feb. 17.
"Having tissue analysis done without a soil test is like
installing new wipers on your car without replacing broken-out
windshield first," said Provin, whose presentation was titled
"Tissue Analysis and Foliar Sprays."
One example Provin cited was of a large pecan orchard in the San
Antonio area. Tissue analysis showed toxic levels of the trace
element boron. The owner was considering shutting down
irrigation wells and buying irrigation water from the city of
San Antonio, a very expensive proposition.
"Eventually, it was not the tissue analysis that helped us find
the problem, but a follow-up soil test," Provin said.
Boron is present in most soils, but a low soil pH made the small
amounts of boron that were present highly available to the
trees. Liming the soil caused the excess boron to chemically
bind with aluminum compounds in the soil, which made it
unavailable to the trees, and corrected the problem.
Tissue analysis can be a valuable tool when the standard
diagnostic tools rule out possible problems such as insufficient
soil nutrient availability, poor water quality, endemic disease
or pest infestations. Tissue analysis is most appropriate for
deep-rooted trees and shrubs where surface applications of
fertilizer are less relevant.
To be of any use at all, tissue samples must be taken according
to strict guidelines. For instance, samples must be collected
from appropriate parts of the plant, and this varies according
to the species. For example, with most trees, leaves are
collected from the middle third of the canopy; for cabbage, the
first mature leaves; and for asparagus, the middle of the stem.
For any plant, call the tissue analysis lab to learn where to
collect the sample, Provin said.
Samples should also be large, not just a single leaf or stem
Wash the samples in a weak acid solution. This is because tissue
analysis is most useful for diagnosing trace element problems
where the nutrient is measured in parts per million. Windblown
dust or improper handling can introduce extraneous compounds
that can compromise the accuracy of the analysis.
An acid wash is performed using a diluted solution of muriatic
acid, available at most hardware stores. Typically, muriatic
acid comes in 20 percent concentrate. This should be further
diluted as one part acid to19 parts distilled water.
At this dilution, the acid is fairly benign, but rubber gloves
should still be worn while cleaning the sample.
The lab will perform the acid wash if desired, he said. If the
sample is sent unwashed, it should be sealed in a press-and-seal
plastic bag and labeled accordingly.
"There are so many factors that influence accuracy of tissue
sampling. More often than not, there's more information found by
a properly taken soil sample," Provin said.
For more information on soil testing or plant tissue sampling,
contact the local Extension office. Contact information for
specific Texas counties can be found on the Internet by using
the following format: Use the county name, followed by a hyphen,
then "tx", then ".tamu.edu." For example,
is the Web site address for the Extension office in Smith
More information can also be found at the soil testing
Approximately 170 local growers, Master Gardeners and homeowners
attended the conference.
Writer: Robert Burns, (903) 834-6191, firstname.lastname@example.org