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Intercepted PAR (MJ m 2 )
Figure 7.4 The effect of seasonal intercepted PAR on total (open
symbols) and fruit (filled symbols) dry matter production from a range
of intensive apple orchards. 'Golden Delicious'/'M.9': spindlebushes:
,1974; ,1975; 'Crispin'/'M.27' bed systems: O,1982; ,1983.
From Palmer (1989a),from Manipulation of Fruiting by C. J. Wright.
Reprinted by permission of Elsevier Science Ltd.
% of the differences (variance) in
yield, in a trial involving two scion cultivars on four rootstocks and with three
pruning systems, was accounted for by a positive linear regression of yield
on intercepted PAR. Similar results have been found in numerous studies,
especially on planting density in modern orchard systems ( Jackson,
Robinson and Lakso (
) found that
;
Robinson,
).
The speed with which orchard canopies obtain high levels of light intercep-
tion is a dominant factor in determining the precocity of orchard yield, which
in turn is a key determinant of profitability ( Jackson et al. ,
).
Where, however, orchards of large trees had formed 'fully closed stands' or-
chard yields were increased by thinning out the trees (Verheij,
; Jackson,
). This pre-
sumablyresultedfromremovingtheadverseeffects ofexcessshadeon fruitbud
formationandfruitset(cf.Chapter
),andthereforeondrymatterpartitioning.
Shade in the immediate environment of apple fruits has pronounced effects
on their size, red colour development and eating quality. There are critical
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