Agriculture Reference
In-Depth Information
season; excessive water content in the rooting medium leads to rotting instead
of rooting.
Root growth of the rooted cutting and
during tree establishment
The growth of roots of rooted cuttings and of orchard trees can be best under-
stood in terms of the environmental factors which affect root growth
per se
and of those involving the functional equilibrium between roots and shoots.
This concept of functional equilibrium (Brouwer,
) is that shoots
and roots are interdependent with each supplying essential materials for the
growth of the other. Thus a reduction in the function of the one generally
results in a reduction in the growth rate of the other (Brouwer and De Wit,
,
), if all other factors remain constant. The general relationship has been
reviewed by Klepper (
). Root/shoot ratios tend to be higher when soils
are deficient in water and nutrients than when these are readily available but
under any given set of conditions plants of all species tend to restore the ratio
between root and shoot when part of either is removed. For example, relative
shoot growth increases and the proportion of dry matter increment going to
root decreases after grazing or defoliation of grasses.
Root growth in the nursery
Following rooting or root initiation in stoolbeds or cutting bins the rootstocks
are transplanted to the site at which they will be budded or grafted with the
scion cultivar.
In the stooling system the rooted shoots are harvested by hand or mechan-
ically from the stoolbed (Howard,
). They usually have numerous roots
but the proportion of root to shoot dry weight is very low. Vyvyan (
) found
the root/shoot ratio of typical rooted shoots taken from a stoolbed of 'M.
'to
be
at the time of harvesting and planting out in April. By December the
stem weight had approximately doubled but root weight had increased more
than
.
-fold to give a root/shoot ratio of
.
, which is within the range
normal for young apple trees (Avery,
).
Inthewinter-cuttingsystem,cuttingsofeasy-to-rootsubjectsmaybeplanted
in the nursery field after only two or three weeks' basal heat treatment in the
cutting bins, with most of them showing only good callus development and
only a few showing roots (Howard,
). Slower-to-root subjects are given
longer exposure to heat and require the presence of a few roots on each cutting
prior to transplanting, but even with these the root to shoot ratio is very low. In
most rootstocks a proportion of the roots developed in the cutting bin survive
transplanting and further roots emerge from the buried rootstock stem during
