Agriculture Reference
In-Depth Information
apple the young leaves develop reddish necrotic spots before the scorched tips
and margins turn brown. The shoots begin to die back from the tips, the
scorched leaves shed and the drying tips curve downwards. Multiple shoot
emergence from below the affected part gives a bushy appearance. Later a
bark necrosis with rectangular cracks may develop. Cu deficiency tends to be
associated with specific soils in limited areas.
Zinc (Zn)
Zinc deficiencies are fairly widespread and may be severe in some environ-
ments.Theinitialsymptomisachloroticmottlingoftheleaves.Thisisfollowed
by a rosetting or tufting of the leaves on the terminal growth. There is little or
no development of leaves on
-year-old wood. Those leaves that develop, ei-
ther in the rosettes or laterally on the shoots, are small and strap-like as well as
chlorotic, hence the common name 'little-leaf disease'. Crops on Zn-deficient
trees are reduced and the fruits are smaller than normal. An excess of Zn
usually appears as Fe chlorosis.
Aluminium (Al)
Aluminium is not thought to be essential for apples or pears. It is, however,
very toxic especially below pH
leading to root malformation, malfunction
and death. The leaf and fruit symptoms are those of Ca deficiency.
.
Nitrogen nutrition
The nitrogen available to fruit trees comes from the mineralization of soil
organic matter and from atmospheric deposition in rain. The balance needed
to meet demand is provided by fertilizers, applied to the soil or to the leaves.
Fertilizer practice is often governed by the need to compensate for N removal
by the orchard surface cover crop, usually grass, and also by the requirement
for additional N in the tree at flowering time. Fertilizer N is most usually
supplied in inorganic form as nitrates or ammonium compounds or in the
organic form as urea.
Under English, humid temperate, conditions on clean cultivated unfer-
tilized orchard soil the amount of mineral nitrogen may increase by
-
kg N ha
−
yr
−
and in a Danish orchard soil annual nitrate production
was
kgNha
−
(Greenham,
). The annual supply of N in rainfall in
Southeast England may be in the range of
kg ha
−
. Under these circum-
stances there may be little or no need for, or response to, N fertilizers. Indeed
the practice of 'grassing down' orchards was introduced to remove soil N and
improve fruit firmness and red colour.
-
