Agriculture Reference
In-Depth Information
intermittently dry soil and the density of rooting increases dramatically where
the roots enter a nutrient and moisture-rich layer (Atkinson,
a). Where
the soil is so managed that certain zones provide better conditions for root
growth than others, the bulk of the roots will be found in these regions, so the
trees are effectively rooted in a medium much richer than the bulk soil.
Factors limiting orchard tree root growth
In general the depth of rooting increases from sand to loam to clay (Rogers
and Vyvyan,
). It can be limited by the presence of a seasonal
water table or mechanical impedance due to hard rock or an impermeable
hard pan and influenced by soil nutrient and water status, temperature and
grass and soil management.
; Coker,
Anaerobiosis
The importance of high aeration to rooting in artificial media has been quan-
tified by Harrison-Murray and Fieldsend (
) and Harrison-Murray (
).
Rooting percentage of 'M.
' apple rootstock increased to about
%atan
air content of
% air few cuttings rooted and most
rotted. There was no evidence that shortage of water limited rooting at a wa-
ter content of
% (v/v) while below
%, the lowest in the trial. In view of the importance of new
root formation in the orchard these results are of relevance to orchard trees,
although the coarseness of the media used restricts the range of soils to which
the results are directly relevant. Wiersum (
)
in arguing that the oxygen diffusion rate (ODR) measured with a platinum
electrode should be above
) cites Stolzy and Letey (
×
−
gO
cm
−
min
−
to ensure good
-
root growth. Webster (
) found that the abundance of small apple roots
<
(
mm diameter) was greatly reduced if soil porosity was less than
-
%
and if less than
kPa tension. The
most common causes of anaerobiosis in soils used for fruit growing are seasonal
water tables (Rogers and Vyvyan,
% of the soil volume was air-filled at
−
) and
excessive water supply to a part of the soil profile as a result of inappropriate
irrigation technology (Levin
et al.
,
), impeded drainage (Weller,
).
Where water tables are permanently high, shallow rooting results. Such
shallow root zones may be adequate. Temporary saturation as a result of heavy
rain or irrigation combined with locally poor soil structure and drainage can,
however,leadtolocaloxygendeficiencyanddeathofrootsintheintermittently
saturated zones. This is especially likely in summer when respiration rates are
high and can lead to nutritional problems accompanying root death (Wiersum,
; Huguet and Fourcade,
).
Anaerobiosis also has a number of important effects on root function.
The accompanying check to respiration and availability of metabolic energy
