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HOW TO COLLECT AND INTERPRET PLANT TISSUE SAMPLES |
Sampling Plant Tissue
Plant analysis is the laboratory determination of several elements on a single sample
of plant tissue. This technique is most commonly used to diagnose nutritional problems
related to soil fertility or to monitor the effectiveness of fertilizer practices on
growing crops.
Plant analysis is not a substitute for soil testing, but is most effective when used in
conjunction with a regular soil testing program.
The number of elements that are measured depends on the laboratory to which the samples
are sent for analysis. The most common elements analyzed in the sample are nitrogen (N),
phosphorus (P), potassium (K), calcium (Ca), magnesium (M), iron (Fe), manganese (Mn),
boron (B), copper (Cu), zinc (Zn), and aluminum (Al). Others that may be measured either
routinely or upon request include sulfur (S), sodium (Na), molybdenum (Mo), cobalt (Co),
silicon (Si), cadmium (Cd), nickel (Ni), lead (Pb), chromium (Cr), arsenic (As), and
selenium (Se). Although some of these are not essential for plant growth, the results may
be used to identify elemental toxicities.
In order for plant analysis to be effective, considerable care must be given to
collecting, preparing and sending plant tissue to the laboratory for analysis.
What to Sample
Proper sampling requires that a specific plant part be taken such as a particular leaf,
group of leaves or portion of the plant. Instructions also include number of individual
parts, as well as the number of plants to sample. This will ensure that a sufficient
quantity of plant tissued is submitted for analysis and that the collected sample is
statistically representative of the area under study.
When sampling mixed stands, particularly forages and pastures, separate plant species.
Similarly, the sample should be of only leaves or petioles or whole tops and not mixtures.
The enclosed table provides plant tissue collection guidelines for many of the crops grown
in New Mexico.
When no specific sampling instructions are given for a particular crop, the general
rule of thumb is to sample the uppermost recently mature leaves.
Young emerging leaves, older mature leaves and seed are not usually suitable plant
tissues for analysis since they so mot ordinarily reflect the general nutrient status of
the whole plant.
The recommended time to sample usually occurs just prior to the beginning of the
reproductive stage for many plants. However, sampling earlier or even later than the
specified time may be recommended for specific plants or circumstances.
Sample plants which are showing a suspected nutrient deficiency symptom at the time or
shortly after the visual symptoms appear. Do not sample or include in a sample plants
under a nutrient stress for an extended period of time, dead plant tissue or plants or
tissue mechanically injured, diseased, or insect-damaged.
Multiple Sampling
When a nutrient deficiency is suspected at time other than specified for sampling, also
collect similar plant parts from normal plants growing in the immediate or adjacent areas.
Take care to ensure that the two sets of plants are at approximately the same stage of
growth and have been treated the same. Comparative analyses are questionable when the two
sets of plants are not at the same stage of growth, have note received the same treatment
or are not the same variety or hybrid. If the soil type varies between the two sites,
tissue analyses would not be comparable. If all the proper conditions have been met, then
a comparison of results between two sets of plant tissue samples can be invaluable to the
interpreter. Do not mix or place the collected tissues in the same mailing kit. When soil
test data are available, take soil samples from both areas.
Washing to Remove Contaminants
Avoid dusty or soil-covered leaves and plants whenever possible. When leaves are dusty,
brush or wipe with a damp cloth to remove the contaminants. If this is not effective or
when leaves are covered with spray materials, wash in a mild detergent solution (0.30
percent) and rinse in running water to remove attached substances. Do not prolong the
washing procedures or allow the plant material to stand in either the washing or rinsing
baths. Wash and rinse briskly. Wash leaves which have been sprayed with nutrient solutions
while they are still fresh. If iron is of primary interest, wash leaves regardless of
their outward appearance. Wash whole plants sampled shortly after emergence to remove soil
particles which are frequently attached to the new tissue.
What Not to Sample
Do not include diseased or dead plant material in a sample. Do not sample or include
plants or leaf tissue which have been damaged by insects or mechanically injured in a
sample. When whole plants are sampled, remove the roots and wash the upper portion to
remove soil particles. Do not sample plants which have been stressed extensively by cold,
heat, moisture deficiency or be excess moisture. Examine both the below ground as well as
the above ground portion of the plant. The presence of nematodes or roots damaged by other
insects or diseases should preclude the need to sample.
Packaging Plant Tissue
Air dry plant tissue samples before shipment to the laboratory. Package samples in
clean paper bags or envelopes for mailing to the laboratory. Never place fresh samples in
a plastic bag.
Plant Analysis Interpretation
The use of plant analysis is an effective management strategy for a sustainable soil
fertility program because it provides a direct measure of nutrient concentrations and
balance within the plant.
Principles and procedures used for plant analyses have evolved over many years and
changed as knowledge increased about each element that is essential for a plant to
complete its life cycle. As such, use of plant analyses has become an integral part of
most agronomic research and a tool for crop consultants and fertilizer dealers to monitor
production fields.
The enclosed table provides plant tissue analysis interpretation guidelines for most
crops grown in the Mesilla Valley.
The effects of time of sampling, variety or hybrid and environmental factors, such as
soil moisture, temperature, light quality and intensity may significantly affect the
relationship between nutrient concentration and plant response.
A defined sufficiency range may not apply to all situations or environments, nutrient
uptake and internal mobility, as well as dry matter changes, can affect the nutrient
concentrations in pant tissues. Concentration and dilution occur due to the difference
between plant growth and nutrient absorption as well as movement of the nutrients within
and between plant parts.
Under normal growing conditions, nutrient absorption, and plant growth closely parallel
each other during most of the vegetative growth period. Exceptions occur during the very
early growth period shortly after germination, after seed set and at the beginning of
senescence. However, if the normal rate of growth is interrupted, nutrient accumulation or
dilution can occur.
Questions about HIT may possibly be quickly answered by
contacting:
Rudy Garcia
Natural Resources Conservation Service
Soil Conservationist & Water Quality Specialist
e-mail: rgarcia@nm.nrcs.usda.gov
or call: 1-505-522-8775, extension 116
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