Agriculture Reference
In-Depth Information
Examples of similar light interceptions achieved with truncated triangular
cross-section hedgerows of different dimensions, spacings, leaf areas, canopy volumes and
canopy surface areas
Table
.
Canopy
Canopy
% light
Canopy
Clear alley
Basal
volume
surface area
thickness (m) LAI (m
m
−
)
(m
m
−
)
interception height (m)
width (m)
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
From Jackson and Palmer (). Reproduced with permission.
at different latitudes. For example, Davis, California has a high-light
climate with
GJ m
−
over a
-month growing season whereas
Wilhelminadorp, Netherlands has an average of only
.
GJ m
−
over
.
a similar period. If
% of above-canopy radiation at Wilhelminadorp is
taken to be the critical level for 'good' apple fruit bud formation and fruit
size development there, the same light intensity will be attained within the
canopy at Davis with only
% of above-canopy irradiance. With
F
max
at
.
and
K
at
.
, the LAI receiving this critical light level in absolute terms
will be
.
at Wilhelminadorp and
.
at Davis, because at Wilhelminadorp
I
L
/
I
needs to be
.
but at Davis only
.
( Jackson,
).
Trunk cross-sectional area and light interception
Trunk cross-sectional area, or girth
, is related to leaf area by equations
.
and
, although both
b
and
K
may vary. Individual tree leaf area can thus
be estimated from trunk girth
or TCA; orchard LAI from the summation of
these.
The relationship between summed orchard TCA and light interception will
therefore follow the relationship between orchard leaf area and light intercep-
tion. It will be a combination of linear effects (e.g. increase in planting density
in the early years influencing
F
max
proportionately) and effects based on the
exponential relationship between light interception and leaf area, as discussed
earlier. The latter will become increasingly important as the trees grow to their
final size with increasing within-canopy shading. This provides the basis for
the good fit of a quadratic curve to the relationship between light intercep-
tion and TCA over a number of orchard systems (Robinson and Lakso,
.
)
and also, at least in part, to the curvilinear relationship between yield and
girth
.
