Maximum Yield Cannabis Canada 2017 July/August | Page 37

Foliar analysis is a great tool for confirming a mineral deficiency diagnosis
when symptoms first start to show.
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 potassium) that are present
or required by fruit. Heavy fruiting crops, such as tomatoes,
partition considerable amounts of potassium into fruit tissue,
so this needs to be considered if using foliar tissue analysis to
formulate a new nutrient solution or adjust a current one.
Perhaps one of the most common mistakes is that while
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
“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.
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