Agriculture Reference
In-Depth Information
Table
.
Mean percentage leaf reflectance, transmittance and absorptance (over the
-
nm waveband) and dry weight per unit area for sun and shade leaves of 'Golden
Delicious' at four occasions during the season
May
June
July
Sept.
Sun leaves
Reflectance
.
.
.
.
Transmittance
.
.
.
.
Absorptance
.
.
.
.
Leaf dry wt/unit
area (mg cm
−
)
.
.
.
.
Shade leaves
Reflectance
.
.
.
.
Transmittance
.
.
.
.
Absorptance
.
.
.
.
Leaf dry wt/unit
area (mg cm
−
)
.
.
.
.
From Palmer (a). Reproduced with permission.
Leaf angles and leaf folding
Jackson (
) found that most of the leaves of 'Laxton's Superb' apple trees
grown as hedgerows had the plane of their laminas at less than
◦
to the hori-
◦
as the most common angle. The leaf petiole was commonly
bent so that the upper surface was at right angles to the incident light, notice-
ably in the lower parts of the trees with shading from above but exposure to
light from the side. In 'Golden Delicious' and 'Goldspur' trees more than
zontal with
-
%
◦
above the horizontal (Wagenmakers,
of leaves inclined less than
b),
although Proctor
et al.
(
) found little preferred inclination or orientation
on bush trees of 'McIntosh' apple.
Johnson and Lakso (
) reported that 'Jonamac' apple leaves are usu-
ally appreciably folded: the leaf folding angle between each leaf half and the
horizontal position averaged
◦
.
Foliage clumping
Apple and pear leaves are obviously not uniformly or randomly distributed
within the orchard space. Extension shoot leaves are systematically arranged
around the stems that bear them and short-shoot or spur leaves are in compact
clusters. In general, the greater the non-uniformity of distribution the less light
will be intercepted per unit leaf area. The same concept of 'clumping' can be
applied at the orchard level: dense individual trees or hedgerows separated by
wide gaps being much more 'clumped' than, for example, orchards of V- or
Y-trellised trees especially if these almost meet above the alleyways.
