Agriculture Reference
In-Depth Information
where
A
is leaf area,
K
is a constant and
G
is branch or trunk girth. This
corresponds to the relationship
KG
b
A
=
(
.
)
The regression coefficient
b
, which determines the slope of the relationship,
was found by Holland (
) to range from
.
to
.
. Other studies gave
similar results.
Equations
can be used to estimate tree or branch leaf area from
girth once
K
and
b
have been determined. Equation
.
or
.
also provides the
rationale for using girth
(which is widely used as a measure of tree weight
because of its close correlation with this, cf. Pearce (
.
), Moore (
) and
Chapter
) as an estimate of tree size in relation to potential assim-
ilation. The limitations to the use of equation
,p.
to estimate leaf area are
that
K
, and to a much lesser extent
b
, vary with factors such as pruning,
cropping level, time of season and tree age, and so need to be established
from samples of the population being studied. For example, leaf area per
tree will level off at maturity, when the trees are pruned to contain them
to the chosen size even though trunk girth and cross-sectional area (TCA)
continue increasing. The limitations to the use of girth
or TCA as a basis
for estimating light interception and potential assimilation are discussed on
p.
.
.
Effects of light interception and of
within-tree shade
Total dry matter production, hence the upper limit to potential yield, is usually
directly proportional to light interception by fruit tree orchards as well as other
crops (Monteith,
; Jackson,
; Palmer,
a; cf. Figure
.
). Light that
is not intercepted by the crop canopy is not used by it!
The slope of the regression for dry matter production on intercepted photo-
synthetically active radiation (PAR) gives
GMJ
−
for the apple orchards
.
studied by Palmer (
a). The efficiency with which intercepted radiation is
used in dry matter production is affected by a number of factors, discussed
in Chapter
on photosynthesis and respiration. Factors controlling the pro-
portion of assimilated carbon which is harvested as fruit are also discussed in
Chapters
. Some of these factors are very important determinants of
orchard fruit yield, especially the differences between cultivars in partitioning
between fruiting and vegetative growth and the differences between rootstocks
in their effects on this partitioning (cf. Table
,
and
). However, with
productive cultivars on efficient rootstocks the yields of well-managed orchards
are largely dependent on their light interception.
.
; Figure
.
