Agriculture Reference
In-Depth Information
(a)
H
H
x
xx
(b)
H
H
x
x
x
x
(c)
x
x
x
x
x
x
Figure 3.6
The root distribution between the surface and 30 cm
depth in a mature apple orchard (
•
,roots
<
2 mm diameter; X,roots
>
2 mm diameter) in relation to the area treated with herbicide
(a) Narrow (0.5 m) herbicide strip (b) wide (1.5 m) herbicide strip
(c) entire orchard surface herbicided. H shows the boundaries of the
area herbicided to each side of the tree row. From Atkinson and White
(1980). Reproduced with permission.
Effects of tree to tree competition
Atkinson (
) showed that the closer the spacing between trees the less the
horizontal spread of their roots and the greater the proportion of their roots
found below
).
'Replant' effects
Planting apples or pears on land previously used for either of these crops may
lead to very adverse effects on root growth and, consequently, on total tree
growth and cropping. This will be discussed in detail in Chapter
cm in depth (Figure
.
.
The above-ground parts of the tree supply carbohydrates produced in photo-
synthesis to the root system, re-export mineral nutrients to it and compete with
it for these resources. There is experimental evidence of the immediate de-
pendency of root growth on current photosynthesis, although the autumn and
spring root growth, which is very important in young trees, obviously depends
on reserves. Defoliation even
weeks before natural leaf fall greatly reduces
apple root growth within two weeks of treatment (Head,
-
a), and removal
of a ring of bark in September also reduces autumn and winter root growth
(Priestley,
). Reducing the light received by the leaves of one-year-old pear
trees reduces root growth in direct proportion and the effect is reversible within
or
days (Lucic,
).
