Agriculture Reference
In-Depth Information
occur pH should be adjusted to
before planting. Under conditions of low
Ca and high Mn the degree and incidence of IBN increase with increasing K
concentrations (Domoto and Thompson,
.
).
Copper nutrition
Copper, in minute quantities, is essential as a constituent of plastocyanin,
which functions as an electron donor in photosystem-
. Enzymes containing
Cuincludeanumberofoxidases.Itisthereforeinvolvedinlignificationandthe
development of xylem vessels (Marschner,
). Copper deficiency, although
rare, can lead to severe shoot dieback and withering of the terminal portions
to the extent that a normal tree framework cannot develop. Affected trees bear
few fruits and, commonly, no crop at all (Beyers and Terblanche,
b).
Copper is generally found at typical trace element concentrations (
<
.
-
%) complexed with
low molecular weight organic compounds (Robson and Pitman,
.
ยต
M) in the soil solution, where it is largely (
-
; Faust,
). It is also found in complexed forms in the xylem. In other plant species
it can be retranslocated from old to young leaves in parallel with nitrogen, so
this may also be the case in fruit trees.
Copper deficiency tends to occur in acid sandy soils and occasionally also
in black alluvial soil with a high humus content. Pre-planting application of
organic matter and pH adjustment reduces the incidence of copper deficiency.
Young trees can be sprayed in spring with copper oxychloride or copper oxy-
sulphate at a rate of
l of water. A second application may be
needed a month later. Bearing trees are sprayed at the green-tip stage at
g per
kg
of either of the same compounds per
l. Sprays during the growing season
can cause fruit russet. Post-harvest leaf sprays or dormant season pre-blossom
sprays can also be used. Potential Cu deficiency may be prevented by the use
of fungicidal sprays containing copper. Soil dressings by broadcasting are not
recommended but a mixture of compost with up to
g CuSO
applied in
holes around the tree may be effective.
Boron nutrition
The most important effects of boron on apple and pear trees are on fruit set
and, secondarily, on fruit quality with the development of external and internal
cork formation and cracking in B-deficient fruits. The B content of flowers of
apple and pear is high (Crassweller
et al.
,
). If the
necessary high levels are not attained then, especially in pears, the flowers wilt
and die but persist on the tree (Batjer
et al.
,
; Johnson
et al.
,
). The incidence of B deficiency
tends to be a problem at a regional level associated with soil characteristics, for
