plant analysis
Micro or trace elements often have a broader
range of normal levels in healthy plants. In tomato,
iron levels should be within the range of 80-200 ppm
and manganese should be between 50-300 ppm,
with iron levels becoming deficient at below 60 ppm
and manganese below 20 ppm.
By comparing the foliar mineral levels returned
on a recent lab analysis to the healthy range for
the plant species being grown, it’s possible to see
which nutrients fall outside the recommended
range. This can help pick up any potential issues
before a stage of deficiency has been reached and
plant growth becomes affected.
Limitations or Issues with Foliar Testing
While plant foliar analysis is an extremely useful
tool, it does have drawbacks and limitations that all
growers using this process need to be aware of. First,
the foliar nutrient levels returned on the lab report
are more representative of plant nutrition at the
time the leaf was forming. For slow-growing crops,
this may have been several weeks ago. By using
both foliar analysis and nutrient solution analysis,
a better picture can be drawn up as to when any
particular element was deficient or needed boosting
in the plants’ feed schedule.
Secondly, if odd results do appear on a foliar
mineral level analysis report, it’s important to
remember that contamination can be an issue.
Copper fungicides, for example, can give incorrect
copper readings of foliar samples and although leaf
samples can be washed before sending off to the lab,
some compounds may become incorporated into the
waxy leaf cuticle and not be removed.
Another factor to consider is that foliar analysis does
not take into account the elements (such as potas-
sium) that are present or required by fruit. Heavy fruit-
ing crops, such as tomatoes, partition considerable
amounts of potassium into fruit tissue, so this needs to
be considered if using foliar tissue analysis to formu-
late a new nutrient solution or adjust a current one.
Perhaps one of the most common mistakes is that
whil e a mineral deficiency problem may show up
in the report, this may not necessarily be directly
caused by a lack of that element in the nutrient
solution. Other factors also affect plant uptake
and nutrient transportation, as well as subsequent
foliar mineral levels. In this case, boosting levels
of the element shown to be low or deficient in the
nutrient solution will not improve the problem. Other
factors need to be addressed. Calcium is a common
example of this, and iron is another. Calcium-related
disorders such as blossom end rot and tip burn in
lettuce and many other plants are a result of a lack
of calcium incorporated into new developing tissue.
However, in hydroponics, where calcium is typically
supplied in most nutrient products at fairly high
levels, a lack of calcium in the root zone is hardly
ever the cause of the deficiency symptoms. In this
case, low foliar calcium levels on a plant analysis
report are often a direct result of growing conditions,
which have limited plant uptake of calcium from the
hydroponics solution. These conditions include high
humidity, warm temperatures, and lack of air flow.
All of these restrict transpiration from the foliage,
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feature
“IT IS USUALLY
beneficial to carry out
both nutrient solution and
foliar mineral level testing,
particularly in recirculating
systems where certain
nutrients may become
depleted rapidly.”
Top: Tip burn on lettuce is an induced calcium deficiency, usually caused by
environmental conditions rather than a lack of calcium in the nutrient solution.
Bottom: Iceberg lettuce has a high potassium requirement and without foliar
analysis, deficiency symptoms are often misdiagnosed as a foliar disease.