The Rural Voice, 1985-09, Page 30MERVYN ERB
Tissue tests
determine plant's progress
Plant tissue testing has become a
major production tool in this area
and has a great future as a diagnostic
tool on vegetable, field, and fruit
crops.
It has been well proven that
humans and animals are "what they
eat." The same principles are true of
plants.
A complete soil test predicts what
should be applied to the soil to pre-
vent a deficiency. A series of tissue
tests can find out errors in fertiliza-
tion and determine how well the plant
is doing nutritionally.
There are many reasons why plants
test low in one or more nutrients and
are not healthy and not growing at a
maximum rate. Nine reasons are: 1.
not enough applied; 2. enough ap-
plied but inefficient placement; 3. im-
proper irrigation early in the season;
4. cold soil temperatures; 5. diseased
seed; 6. compaction. poor soil struc-
ture, and poor aeration; 7. insect and
disease damage; 8. application too
late; 9. leaching with excessive water.
Soil tests and tissue tests cannot be
substituted one for another. They go
hand in hand. The object is to keep
nutrients in the sufficiency range (not
too high and not too low).
There are two approaches we can
take with tissue tests.
First, the monitoring approach.
With this approach, we take tissue
samples routinely — perhaps every
few weeks. Samples are taken from
fields even though they are green and
appear to be healthy.
We look for the unseen problem
(hidden hunger) with chemistry and
evaluate for nutrient levels. This
enables us to head off a major
28 THF RURAL. VOICF
Mervyn Erb,
a regular
contributor
to the Rural
Voice, is
crop
specialist at
the Hensall
District
Co-op
nutrient deficiency that would have
taken place later in the season.
By having a season -long nutritional
record, we can use the data for
evaluating production in future years.
Second, the diagnostic approach.
This approach is used to determine
what is wrong with a crop after one
suspects that there is a problem. The
tissue test may disclose a nutrient im-
balance and a deficiency of one or
more nutrients. If the test is taken in
time it is possible to correct the pro-
blem. One difficulty with this ap-
proach is that the results could be a
funeral report. A funeral report in-
dicates that it is too late even to try to
correct the nutritional problem for
the current crop year.
The better method to use is the
monitoring approach. This is because
a single test does not tell whether the
concentration of nutrients is going up
or going down. The use of bi-monthly
samples will show us trends in the
curve and allow us to make predic-
tions.
Many years ago, agronomists made
use of plant deficiency symptoms. It
is now known that deficiency symp-
toms are not clearly defined, and that
they have limited value. The same
symptom may be caused by the defi-
ciency of two or more nutrients. The
presence of diseases and insects can
also prevent accurate field diagnosis.
Deficiency symptoms always in-
dicate severe starvation, never slight
or moderate starvation. Most crops
begin to lose yields well before defi-
ciency signs start showing. This costly
period is called hidden hunger. As a
result, there is a real need for tissue
testing.
Tissue testing evaluation and recom-
mendations
After a tissue test is made, it must
be interpreted properly and acted
upon if need be. The following are
some principles which should be kept
in mind.
• Concentrate first on the major
nutrients (N,P,K) and then on the
micro -nutrients. A major nutrient
deficiency can alter the level of
another nutrient. For example, if
nitrogen is deficient, it is common to
observe a decrease in P, K, Zinc, and
manganese.
• If nitrogen is deficient, the deficien-
cy can be corrected by applying
nitrogen in irrigation water by air or
through sidedressing with a "High -
Boy."
„
• If phosphorous is deficient, then li-
quid sources of phosphorous can be
added in the water or in a foliar
nutrient spray.
• A sulphur shortage can be corrected
by applying sulphur in the water or by
adding sulphur in a foliar spray.
• The best way to correct micro-
nutrient deficiencies is to add foliar
nutrient sprays by air or by ground
application.
• Based upon the time of year and
nutrient levels, the tissue test levels
may result in the interpretation of a
funeral report. It may be too late to
correct the deficiencies.
Foliar feeding
The only reason to add foliar
nutrients is to correct or prevent a
deficiency. In this area, the most
commonly used nutrients for foliar
application are N and P and the
micro -nutrient zinc. Tissue test
results will determine whether foliar
nutrients can be profitably applied.
All essential nutrients are absorbed
through the leaf surface (waxy cuti-
cle) or through the somata. Only a
small quantity of micro -nutrients and
phosphorous are necessary when ap-
plied foliarly. The efficiency of ab-
sorption of foliar nutrients is much
greater than that of soil -applied
nutrients. The soil ties up nutrients
whereas nothing is present to decrease
the availability of foliar nutrients.
The overall advantages of using a
modern tissue test progam are: 1. to
prevent serious deficiencies from tak-
ing place; 2. to assure more accurate
regulation of the nitrogen supple
prevent over or under -fertilization; 3.
to determine whether extra
phosphate, potash, sulphur, and