Agriculture Reference
In-Depth Information
Faust (
) found the volume of regenerated roots in solution culture to be
twice as high following root pruning as in unpruned controls.
Root/shoot ratios
These are highly variable depending on soil type, tree age, rootstock and the
supply of water and nutrients. Rogers and Vyvyan (
) found the ratio of root
to shoot weight of
-year-old trees to range from
-
.
to
on sandy soils but
from only
.
-
.
to
on loam soils. Very young trees may have a ratio of only
) found that moisture stress, fluctuating soil
moisture availability and waterlogging, which all checked total tree growth,
led to increased root/shoot ratios. Rogers and Head (
.
to
(Avery,
). Cripps (
) concluded that the
ratio is a rough measure of the fertility of a soil. The poorer the soil in terms of
water and nutrient supply, the higher the ratio of roots to shoots. Apple trees
growing in a high-light environment have much higher ratios of root to shoot
than when grown under shade or in a naturally lower-light climate (Cripps,
).
Atkinson (
b) showed that the root/shoot ratio increased progressively
with increasing phosphorus and nitrogen deficiencies.
Functions of roots
Anchorage
The firmness of tree anchorage in the soil is dependent on the depth and
distribution of the root system, the mechanical strength of the roots and the
forces acting on tree stability, primarily wind and the weight of crop.
Apple seedling rootstocks and the clonal rootstocks 'M.
', 'MM.
' and
'MM.
' anchor trees firmly so that they do not require staking. The use
of 'MM.
' was largely discontinued due to poor anchorage combined with
excessive vigour (Ferree and Carlson,
). Apple trees on 'M.
', 'M.
' and
'M.
' often show poor anchorage and tree leaning but not to an extent which
justifies all trees being staked. 'Malling
' and most of its dwarfing derivatives
have brittle roots with short fibres and a high proportion of root bark to woody
tissues. Under severe windy conditions even their large structural roots will
break off cleanly at the base of the trunk. This problem is exacerbated by the
very high ratio of crop weight to tree framework, including roots, in trees on
dwarfing rootstocks (cf. the general negative relationship between crop yield
per unit of tree size and tree size itself, discussed earlier). All apple trees on
dwarfing rootstocks, with the possible exception of those on 'MAC.
' ('Mark'),
are usually supported either by an individual stake or by a post-and-wire
trellis system. This is, however, not solely for reasons of anchorage. It is also
