calcium nutrition
Many
prone to
tables are
leafy vege
, a calciu
g tip burn
developin
issue.
m-related
What Does Calcium Do?
Calcium is an essential macronutrient
required for plant growth along with
nitrogen, phosphorus, potassium,
sulfur, and magnesium, and is typically
supplied at rates of 80-240 parts per
million in nutrient solutions. Calcium
is a vital component of cell walls and
membranes and is deposited during cell
wall formation. Calcium is also required
for the stability and functioning of cell
membranes. When in short supply, cell
membranes become “leaky” and cell
division is disrupted, causing abnormal
growth often in the form of a twisting or
cupping of the newer foliage. Calcium
is also important in maintaining quality
and good shelf life post harvest by
slowing the aging of plant tissues and
protecting from toxins. Calcium is almost
totally immobile in the plant, as it cannot
be mobilized and moved around the plant
once deposited in cell walls. Therefore,
any deficiencies in calcium occur in the
newest growth and include tip burn in
lettuce, strawberry, and many other leafy
crops, and blossom end rot of tomatoes
and capsicum fruit. Other calcium
deficiency symptoms vary between plant
species and degree of severity. Apart from
cupping of new foliage, other symptoms
include a pale marginal band, yellowing,
54
feature
water-soaked areas on foliage and
stems, and root tips that can become
almost jelly-like. Calcium deficiency
can also be difficult to diagnose with
foliar analysis as tissue of different
ages commonly have varying levels
of calcium. Older leaves may show
sufficient foliar levels of calcium under
analysis, but fruit or newly developing
leaves or leaf tips of the same plant
may have deficient levels—it all comes
down to which part of the plant is
sampled. Typical healthy foliar levels of
calcium also differ between species. For
lettuce, foliar calcium levels typically
fall within the 0.8-2.0 per cent range; for
tomato, 1.2–2.5 per cent; and cucumber,
2.0–4.0 per cent.
Tip burn is one of the physiological
problems that cool season salad crops
are prone to in warmer climates and
under greenhouse or growroom produc-
tion. Some commercial growers have
reported losses of up to 50 per cent of
“
TIP BURN
is one of the physiological
problems that cool season
salad crops are prone to
in warmer climates and
under greenhouse or
growroom production.”
their crop to tip burn at certain times of
the year. What is highly detrimental is the
tip burn that can occur inside the head of
lettuce varieties that form a tight heart
of leaves. While the outside of the plant
may look perfect, when cut open, all the
inner leaves can be severely affected by
tip burn, which tends to form a blackened
rotting mass as pathogens start to decay
the dead tissue. While there are differ-
ent types of tip burn, the most common
form is caused by a lack of calcium in the
tissue on the very edges of the leaves—
when tissue is deficient in calcium, the
cell walls begin to disintegrate and break
down, resulting in dead leaves that then
dry up or rot depending on how high the
humidity levels are.