Agriculture Reference
In-Depth Information
Density of rooting
Apple trees, and to a lesser extent pear trees, have very sparse root systems.
Reported values of L A (cm root per cm soil surface) for apple are in the range
of
.
to
.
and for pear from
to
(Atkinson,
). The corresponding
range of L v values (cm root per cm soil volume) is from
.
to
.
for apple
and
for pear. The very low values may reflect limited exploitation
of soil well away from the trunk but even the highest values, obtained from
very closely planted trees, are very low compared with those of conifers ( L A
for Scots Pine
.
to
.
).
Density of rooting can be affected by soil type (Fernandez et al. ,
=
)or Gramineae ( L A values of
-
)as
well as being greatly increased in the vicinity of trickle irrigation emitters and
localized nutrient-rich pockets.
Root death and root system renewal
Rootsystemsareconstantlyinaprocessofdeathandreplacementofindividual
roots. Following the browning of the cortexof young roots this generally decays
and disintegrates, largely due to the feeding of soil fauna. Some roots then
thicken and become part of the perennial root system but many of the lateral
roots, especially, simply disappear (Head,
b). Three types of root death
are distinguished (Rom,
).
A systematic dying of short laterals on active roots, following suberization
of the roots from which they arose, after
-
weeks.
Tips of main roots and those of higher branching orders often die back
while lateral roots continue to grow.
Fibrousrootsmorethan
yearsoldmaydiebackcompletely,tobereplaced
by new fibrous roots.
Even skeletal or semi-skeletal roots may die, particularly after age five. Any en-
vironmental stress increases root shedding and this is also particularly obvious
at budbreak and early in the growing season.
This pattern of root death makes an appreciable contribution to soil organic
matter status.
All parts of the root system except for the tips appear capable of producing
lateral roots from primordia in the pericycle while the tip itself exerts apical
dominance on branching. Death of root tips is thus likely to encourage new
branching. Tamasi (
) found that when roots are cut they develop callus
and produce many new roots near the cut surface, presumably associated with
increased auxin activity such as that demonstrated by Carlson and Larson
(
) after pruning oak roots. Tamasi found that when
roots were cut back
a total of
new roots developed over
years from near the cut surfaces and
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