Agriculture Reference
In-Depth Information
Symptoms of deficiency or excess
Nitrogen (N)
Nitrogen deficiency is characterized by reduced top growth with short upright
spindly shoots bearing pale yellowish-green leaves. The symptoms become
more severe as the season progresses and fruits are usually smaller than on
trees with adequate N concentrations. Excessive N content reduces the area
and intensity of red colour on red cultivars of apple, delays maturity, shortens
storage life and increases susceptibility to some storage disorders, especially
those associated with low Ca concentrations. Trees with excessive N levels
show very vigorous growth and dark green leaves.
Phosphorus (P)
Phosphorus deficiency is uncommon in most fruit-growing areas. It is evi-
dencedbyverydarkgreenleaveswithsomepurplishdiscolorationonthelower
sides, especially on the margins and main veins. Active vegetative growth is
inhibited. Excess P leads to interference with zinc, copper, iron or manganese
uptake and may be one cause of symptoms of deficiency of these.
Potassium (K)
The most characteristic symptom of potassium deficiency is a reddish-brown
scorching of leaf margins, often preceded by a greyish-green discoloration. Ex-
cess K may increase the fruit symptoms of Ca deficiency and the leaf symptoms
of Mg deficiency.
Calcium (Ca)
Calcium deficiency is shown by the upward cupping of the margins of the
youngest leaves. The expanding leaves develop uniform veinal and interveinal
chlorosis, and the very youngest leaves may become entirely chlorotic. Margins
of older leaves may shatter and terminal shoots die back. Bitter pit may develop
as slight indentations in the skin in the orchard or in store. These areas turn
brown,anddesiccatedtissuedevelopsbelowthespots.Corkspotdevelopsearly
as small blushed areas of skin above hard brown spots. Lenticel breakdown
shows as pale areas, later white halos that turn brown or black, around the
lenticels. Sunburn on fruits may be more pronounced when they are Ca-
deficient. Calcium effects are discussed in much more detail in Chapter
.
Magnesium (Mg)
Magnesium-deficient leaves of apple show a colour-fading around the mar-
gins followed by interveinal chlorosis from the margins inwards leading to a
'herring-bone' pattern. Tissues around the margins, especially towards the
