Download Let`s Talk About Micronutrients: Zinc Deficiency

Let’s Talk About Micronutrients:
Did you know that zinc deficiency in plants is often
referred to as “little leaf” syndrome?
Zinc Deficiency
Fig.1. Symptoms of ‘little leaf” or zinc deficiency in corn. Plants lacking
zinc will be dwarfed compared to healthy plants.
Role of Zinc:
Plant species differ in their need for zinc but this
micronutrient is an integral component for the plant growth
regulator auxins and indole acetic acid. It acts as a
catalyst in enzymes vital for protein synthesis and
carbohydrate metabolism especially for C6 (glucose,
fructose) and C3 sugars. If zinc deficiency occurs,
carbohydrates will accumulate and under high light
intensity toxins can build up, impairing new plant growth.
Zinc is also important in the development of chloroplast
(where photosynthesis occurs). Plants with low levels of
zinc also have reduced disease tolerance especially
against Rhizotonia Spp. (a common cereal root rot
pathogen). A deficiency can also limit the size of the plant
by shortening the distance between the nodes and
producing smaller leaves, hence the “little leaf”.
Peak demand for zinc starts during the plant’s early
vegetative stage and remains in high demand through
flowering all the way to seed set. The demand for zinc by
the plant reduces once the grain filling stage begins.
Zinc is directly correlated with nitrogen and plays a critical
role in protein synthesis. Sufficient levels of zinc in a plant
can enhance the nitrogen use efficiency of the plant.
While crops rarely remove more than 225 g/acre of zinc
per year, a deficiency can seriously impair crop yield and
quality.
Fig. 2. Plants deficient in zinc are often dwarfed.
Zinc Deficiency Symptoms:
Plants vary in their mobility to move zinc within their
tissue, but it is not likely to move in the soil. Soil texture,
pH, phosphorous levels and weather can all affect the
plants’ ability to uptake zinc.
Plants grown in sandy soils with low soil organic matter or
areas where topsoil has been removed, like roadsides,
can often show symptoms of deficiency. High manure
rates or high soil phosphorus can often tie up zinc,
causing deficiency symptoms. When the soil’s pH >7.5,
iron and aluminum oxides can bind with zinc to reduce
plant availability.
It is common to see zinc deficiency in crops under cool
and wet conditions however a change in growing
conditions can improve the plant’s ability to take up zinc.
Zinc deficiency can often reduce seed size and set and
may have a significant impact on yield.
Let’s Talk About Micronutrients:
Zinc Deficiency
Fig. 3. Cereals deficient in zinc will display chlorotic stiping with the
center showing grey or brown. It may also have an oily film appearance
to the lesions as well. (arrow). The crinkling of the leaf margins which is
another distinct sign of zinc deficiency.
Zinc deficient cereals leaves will display chlorotic striping
and are sometimes misdiagnosed for leaf disease. Often
the leaves show healthy green margins while the center is
spotted. Necrosis can appear in this center and spread to
the margins of the leaves. Leaves in cereals and corn
often crinkle.
Durum has a high zinc demand and potential high yields
can induce zinc deficiency sooner than other cereal crops.
Legumes with low zinc levels have smaller leaves and
often show bronzing on the older leaves. Beans are
particularly sensitive to marginal zinc levels including
fababeans. Soybeans have a moderate demand. Canola
and corn can also have a high demand for zinc.
Addressing a Deficiency: Western Canadian soils are
typically zinc sufficient however soils may have variable
zinc levels within fields. Zinc fertilizer requirements are
often so small at grams/acre that it is often blended and
applied with N-P-K fertilizer.
Foliar applications can also be effective to address zinc
deficiency and studies show the plant’s ability to recover
from a minor deficiency can be within days.
Photo by C. Holt
Fig. 4: Corn has a high demand for zinc and a deficiency will often show
chlorotic striping and crinkling of the leaves.
Zinc in Humans
Zinc deficiency is often marginal in humans but affects the
health of 2.2 billion people worldwide. Unfortunately, the
most serious zinc deficiency often affects children under
five in developing countries.
Date Issued: April 7, 2017