Agriculture Reference
In-Depth Information
The young root is initially white and succulent with short root hairs usually
.
-
.
mm in length (Rogers,
; Rogers and Head,
). It grows at
up to
weeks it begins to turn brown and the root
hairs shrivel. The browning takes
cm per day. After
-
-
weeks in summer and up to
weeks in
winter (Head,
) and is followed by decay and disintegration of the cortex
due largely to the feeding of soil fauna. Some of the roots become secondarily
thickened and form part of the perennial root system (Head,
b), others
remain unthickened or disappear.
Casparian strips and lignified thickenings differentiate in the anticlinal walls
of all endodermal and
phi
layer cells respectively,
mm from the root tips
in apple. Suberin lamellae are laid down, on the inner surface of endodermis
cell walls only,
-
mm from the tip and an additional cellulosic layer about
mm from the tip. Browning, phellogen development, and sloughing off
of the cortexcommences
mm from the tip. Plasmodesmata traverse the
suberin and cellulose layers of the endodermis and are especially frequent in
the
phi
layer (MacKenzie,
).
The growth of the root system in the orchard is controlled by temperature,
soil moisture and nutrients, the supply of carbohydrates and plant growth
substancesfromtheshoot,andbywithin-plantandbetween-plantcompetition
for these resources.
Slow growth of extending roots may continue through the winter but rapid
new growth in the spring usually begins when the soil has warmed to about
◦
F(
◦
C) (Rogers and Head,
.
). The roots can spread to
feet (almost
)
concluded from earlier studies that the root system is generally more extensive
than the shoot system and will grow in any soil area which supplies what it
requires, subject to limiting factors. Atkinson (
m) on either side of the trunk in the first year after planting. Rogers (
) cites studies in which the
roots of 'M.
' apple rootstocks grafted with different cultivars extended to
m
in depth and
Malus sieversii
rootstock roots to
m, and the radial spread of
roots of a range of rootstocks grafted with 'Cox' covered up to
.
m
and those
m
. This extensive root distribution greatly exceeds
the zones in which most of the roots are found in modern orchard systems
and should be regarded as showing the potential. In New Zealand the roots
of 'average' mature apple trees on 'MM.
of 'Papirovka' covered
' rootstock under good growing
conditions can completely explore, although not fully occupy, the soil volume
between trees spaced at
m
×
.
m to a depth of at least
.
m (Hughes and
Gandar,
).
The actual root distribution can best be understood by considering root
systems as highly plastic entities, the form of which reflects the availability
of water and nutrients. Where the soil is highly heterogeneous in these re-
spects roots tend to proliferate where conditions are favourable for growth,
i.e. the roots may be few and far between when passing through infertile or
