Page 16 - Griffin Gazette Fall 2016
P. 16
Micronutrients
ARE BIGGER THAN YOU THINK
Image: Seed geranium with micronutrient toxicity caused by low pH
By Rick Yates, GGSPro Technical Services Manager example because it contains some iron, but levels of
other nutrients may be raised well above those required
Micronutrients by definition for optimal growth. Overfertilization is expensive and
are required by plants in small can lead to other unintended consequences such as
quantities, but they’re crucial increased susceptibility to insects, mites1 (elevated
none the less. Justus von nitrogen) or excessive internode elongation2 (elevated
Leibig’s Law of the Minimum phosphorus). Elevated soluble salts levels in the media
can be summarized this way, can also occur, potentially leading to inhibition of growth
"The availability of the most or plant damage.
abundant nutrient in the soil is
only as good as the availability Regular media testing can take the guess work out
of the least abundant nutrient in of optimizing nutrient levels. Individual micronutrients
the soil." are available for supplementation, as well as
micronutrient packages that contain most or all of the
A practical application of that law would be to say that a essential micronutrients when multiple micronutrients
plant which is chlorotic and making subpar growth due are deficient.
to a micronutrient deficiency will not be improved by
applying more nitrogen. Leibig’s law has been explained Media pH plays an important role in the availability
by using the image of a barrel where each stave of the of micronutrients to plants. Boron, copper, iron,
barrel represents a different nutrient. Each stave is at manganese and zinc are optimally available for many
a different height that is based on the sufficiency of crops with a pH in the range of 5.2-5.8. Molybdenum
that nutrient. The shortest stave (nutrient) dictates as well as the important secondary nutrients calcium
how much liquid the barrel will hold before it gushes and magnesium are more available with a media pH in
out through that opening. The shortest stave has to be the range of 6.0-6.6. It’s important to understand the
raised in order for the barrel to hold more liquid. (See requirements of the crops being produced. Certain crops
Image 2) Therefore, an iron-deficient plant will not be such as calibrachoas, petunias and flowering vinca are
improved by the addition of more N-P-K, because iron produced in a lower media pH range to optimize the
remains the limiting factor. availability of iron and other micronutrients. Other crops
such as geraniums (seed and zonal) and pentas are so
Grasping this concept can help to avoid overfertilizing efficient at taking up micronutrients that the lower pH
plants. Increasing the amount of a balanced fertilizer ranges favored by the previously mentioned crops can
may improve crop growth in our iron deficiency
16 | Griffin Gazette Fall 2016
