Agriculture Reference
In-Depth Information
The degree of dwarfing which is needed to achieve the most desirable tree
vigour depends on a number of factors:
The vigour of the cultivar: a tree of a vigorous cultivar on a dwarfing
rootstock may be of similar size to a tree of a compact cultivar on a semi-
dwarfing rootstock (Table
.
). Trees of 'Fuji' on the dwarfing 'M.
' root-
stock can be from
%to
% larger than trees of 'Redchief Delicious'
on the more invigorating 'M.
' rootstock (Costa
et al
.,
).
The vigour of the site: there are large differences in this, not just because
of variations in light and temperature at different latitudes (Wagenmakers,
) but also because of much more localized differences in soil fertility.
The standard clone of the most widely used dwarfing rootstock, 'M.
', is
not sufficiently dwarfing in some areas of the Netherlands where natural
soil fertility is high (Wertheim,
).
The tree training and pruning system and its effects on vigour: in general
the training of the main axes into a horizontal or low-angled position, as in
horizontal or Y- or V-trellis systems of tree management, will induce fruit-
fulness and check vegetative growth. Robinson (
) found that Y-trellis
trees were smaller in terms of trunk cross-sectional area than vertical-axis
trees.
The light intensity: areas with higher light intensities have a greater depth
of canopy which is adequately illuminated for the production of fruit buds
and good quality fruits. In such areas there may also be a need for more
leafy canopies to reduce the risk of fruit sunburn.
The light requirements of the cultivar: large-fruited and green-skinned
cultivars, for example, may be able to produce good quality fruits over a
greaterdepthofcanopythansmall-fruitedandpartially-colouredcultivars.
Now there are rootstocks available which will give any desired degree of apple
tree size control. The scion cultivar that at maturity would give a tree more
than
m high and with corresponding canopy spread if on a seedling rootstock
may be restricted to about
'
rootstock. Other rootstock cultivars give all levels of vigour control in between
(Table
.
m in height and spread if grown on the 'M.
.
, Figure
.
).
Effects on precocity of cropping
Apple trees are perennial and although the costs of establishing an orchard
are incurred in the year of planting or even, with respect to land preparation,
in earlier years, returns are not received until the orchard bears fruits. This
difference in time has important economic consequences because of the effects
of real or imputed interest charges. The returns from the crop of each year
need to be adjusted for the timing of these returns in years from planting
