Agriculture Reference
In-Depth Information
Figure 7.9
Comparison of estimates of canopy volumes (m
3
m
−
2
orchard) receiving more than 40% (CV
0.4
)
or more than 20% (CV
0.2
)
of full daylight (daily integrals) for N-S oriented hedgerows 1.5 m
wide at ground level giving all combinations of LAI 1,2,3 and
4,between row spacings of 2 m and 4 m,heights of 1 m and 3 m and
rectangular and triangular profiles in section. 'Palmer model' is the
computer model of Palmer (1977b). The equations are equation 7.8
and those preceding it in this text. From Jackson and Palmer (1981)
with permission.
to any chosen contour of mean irradiance where
(leaf area density m
m
−
)
CV
I
=
L
I
/
(
.
)
It follows from this analysis:
That potential orchard light interception and yield cannot be predicted
from such factors as tree height, surface area, LAI, etc. alone; virtually
identical levels of light interception can be achieved with very different
tree forms and LAI values (Table
.
).
That, especially for tall hedgerow orchards, light interception and distribu-
tion are partly controlled by orchard geometry in relation to direct-beam
solar radiation. North-south hedgerows are generally preferable to east-
west ones and latitude influences the effect of orchard geometry.
That light interception per unit leaf area is higher the greater the value of
F
max
. This is because, at the extremes, increasing orchard leaf area by in-
creasing
F
max
may have a linearly proportional effect on light interception
(e.g. with higher plant populations in the first years after planting). On the
other hand, increasing orchard leaf area by increasing leaf density within
a constant canopy volume will increase light interception in proportion to
the increase in the logarithm of leaf area only.
The actual light intensities within the canopy are a function of above
canopy irradiance. This has implications for optimal canopy dimensions
