Use of Plant Analysis as a Diagnostic Tool
By Manjula Nathan
Plant analysis has been used as a
diagnostic tool for many years. Plant
analysis and soil testing go hand in hand.
To determine nutrient deficiencies, most
agriculturists rely primarily on visual
symptoms, plant tissue analysis and
soil analysis. Plant analysis can be used
to diagnose or confirm diagnoses of
visible symptoms or to identify "hidden
hunger" where a plant may be suffering
from a nutrient deficiency but show no
symptoms, and to suggest additional
tests or studies to identify problems in
a field.
Use of plant analysis in today's agriculture
- Tool for diagnosing nutrient deficiency.
- Use as a monitoring tool to assess the nutrient status of plants in relation to the fertilizer program used. Used in evaluation of crops in a given soil, many times farmers and their crop consultants will develop fertility program and want to know whether there is a need for future adjustments.
- End of season corn stalk NO3- N test at one to three weeks after black layer stage is used at Iowa State to evaluate the previous season N management practices. If NO3-N test in the stalk (cut at 6" above ground level to obtain an 8" long stalk sample) is less than 250 ppm N it is considered as low, and 250 to 700 ppm N is marginal, 700 to 2,000 ppm N as optimum and greater than 2,000 ppm as excess.
- Measuring NO3-N content on corn, wheat or forages after drought or freeze damage if used for feeding livestock to check for nitrate toxicity.
- For perennials and trees that have a tap root system (blueberries, apples, grapes, peach, etc.,) tissue testing is the only way by which you can monitor the plant's nutrient needs.
- For turf nutrient management evaluation.
How to take samples
The normal tendency of individuals
is to collect the stunted plants and
conduct an analysis of the plant
tissue to diagnose a nutrient related
problem. Plant sampling, however, is
more complicated if we expect tissue
analysis to be an effective diagnostic
tool. Technologies and procedures used
in the collection of plant samples vary
with the intended purpose. Instructions
for sampling and submitting samples as
specified by the lab should be followed
to get meaningful results. If specific
sampling instructions are not found
for the crops, the general rule of thumb
is to sample upper, recently matured
leaves. The recommended time to
sample is just prior to the beginning of
the reproductive stage for many plants.
Paired samples
Where a deficiency is suspected,
take samples from normal plants in
an adjacent area as well as from the
affected area. You will be charged the
price of one and a half sample when an
abnormal sample is accompanied by a
normal sample. It is important to take a
soil sample from each area. Comparing
soil and plant analysis results can greatly
assist in the interpretations.
Handling Procedures
Collected plant tissue is very
perishable and requires special handling
to avoid decomposition. Therefore,
fresh plant tissue should be placed in
clean paper bags left open; partially
air dried if possible or kept in a cool
environment during shipment to the
laboratory. Wash dusty plants before airdrying.
Fresh plant samples should not
be placed in closed plastic bags unless
the tissue is either air-dried or bag and
contents are kept cool (40 degrees). Airdrying
of fresh plant tissue can be done
by placing the plant tissue in an open,
dry environment for 12 to 24 hours.
Air died samples can be place in a clean
brown bag or envelop and take mailed
to the lab.
What Not To Sample
- Tissue covered with soil or dust
- Plants damaged by insects, mechanically injured, or diseased
- Tissue from dead plants or tissues
- Plants under moisture or temperature stress
- Plants markedly effected by nutritional stress
- Border-row plants or end-row plants
- Plants in weed infested areas
- Whole plants unless seedlings
How, when and what part to sample?
Since the results of the plant
analysis will be compared to known
standards, it is important that parts of
plants are sampled at a certain stage of
development.
Some examples of field crops
sampling guides are given below:
Corn
When to sample?
Some time between emergence and
silking/pollination. Do not sample after
silks have dried. Nutrient concentrations
decline substantially after this point in
the life cycle and recognized standards
cannot be used for comparison.
Plant part to sample:
Seedling stage- all above ground
portion (10-15 plants). Prior to
tasseling- the entire leaf fully developed
below the whorl (10-12 plants).
Tasseling and shooting to silkingthe
entire leaf at the ear node (10-12
plants)
Soybean
When to sample?
The ideal time is when the first
bloom appears. However, if problems
appear prior to bloom, a sample can
be taken. Do not sample after the first
pods begin to fill.
Plant part to sample:
Seedling stage- all the above ground
portion (10-15 plants). Prior to or
during flowering- Two or three fully
developed trifoliate leaves at the top of
the plant. (10-15 plants).
Small Grain
When to sample?
Any time before head emerges.
Plant part to sample:
Seedling stage- all the above ground
portion. (15-30 plants). Prior to
heading- select tissue from upper one
third of plant. (15-30 plants).
Alfalfa and Clovers
When to sample?
Just prior to bloom (1/10 bloom) or
at harvest stage.
Plant part to sample:
Take top 6 inches of plant or top 1/3
of plant. (20-25 plants).
Sorghum
When to sample?
Ideal time is when head is fully
emerged but before pollination. Samples
may be taken at earlier stage if problem
develops.
Plant part to sample:
Fully expanded and mature leaves.
(10-12 plants).
Cotton
When to sample?
Before bolls start to set.
Plant part to sample:
The most recently matured leaves.
(15-20 plants).
When specific information is
not available use general rule
of thumb
If specific sampling instructions
are not found in the selected crops,
the general rule of thumb is to sample
upper, recently matured leaves. The
recommended time to sample is
just prior to the beginning of the
reproductive stage for many plants.
Submitting Plant Samples
Samples can be submitted to the
County Extension Centers or to the
lab directly. Plant Analysis Information
forms can be picked up at the County
Extension Centers or at the University of Missouri Soil Test Lab free
of charge or can be printed from the lab's
Website at http://soilplantlab.missouri.
edu/soil. Each sample submitted to
the lab should be accompanied by
a Plant Analysis Information form.
When submitting a sample to the lab
the sample information form should
be filled out accurately for the lab to
properly interpret the plant analysis.
Send the original form with the plant
sample(s) to the following address and
retain a copy for your records.
MU Soil and Plant Testing Lab
University of Missouri Columbia
23 Mumford Hall
Columbia, MO 65211
Tel: 573-882-0623
Fax: 573-884-4288
E-mail :SoilTestingServices@missouri.edu.
Web: http://soilplantlab.missouri.edu/
Manjula V. Nathan, Director,
MU Soil Testing and
Plant Diagnostic
Service Laboratory
NathanM@missouri.edu
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