Agriculture Reference
In-Depth Information
cm of the drip points with very few roots more than
cm away. Goode
et al.
(
) also found, after the introduction of trickle irrigation, that roots
proliferated in the wetted zones and there was a reduction in rooting distant
from the point of irrigation. The mutability of the root system in response to
relative water availability is a very important consideration in the introduc-
tion and long-term use of drip irrigation and other high-frequency irrigation
methods.
Soil temperature
In apple the onset of root growth seems to occur at
◦
C (Rogers,
) and
the rate of root growth to be temperature dependent, in England reaching its
maximum in June and July at soil temperature of about
.
◦
C (Rogers and
-
Booth,
). The resultant seasonal pattern of root growth may, however,
be modified by concomitant changes in soil moisture availability and also
by competition from shoots and fruits for resources. Gur
et al.
(
-
a) found
◦
C although there are differences in
rootstock tolerance of high temperature (Nelson and Tukey,
adverse effects of temperatures above
; Gur
et al.
,
b). Rom (
), in a review, concluded that new root formation in
Malus
◦
C roots lack succulence and suffer from early
death of the cortex. The number of active roots in the top
◦
C and above
ceases at
cm of soil
may be limited by high temperatures in hot-desert climates. In cold-winter
climates surface roots may be killed by winter freezing in lighter textured and
drier soils without snow cover: differences in freezing tolerance of different
rootstocks have been discussed earlier (pp.
-
)
Effects of grass competition and soil management
The lateral spread of apple root systems is checked by competition from grass.
Where trees are grown in herbicide-treated strips separated by grassed alley-
ways most of the roots are confined to the herbicide-treated strip (Figure
.
;
Atkinson and White,
).
Under the older management system of cultivating the orchard, surface
roots growing in the top
cm of soil were pruned annually. When the or-
chards were grassed tree roots grew nearer the surface but were subject to
direct competition for water and nutrients (Coker,
). Eliminating grass
and weed competition either in herbicide-treated squares of
m
around
.
the base of the trunk (White and Holloway,
) or in herbicide-treated strips
along the tree rows, or when the entire orchard surface was herbicide-treated
(Atkinson and White,
), resulted in more apple roots in the surface
layers of the soil. Apple trees grown with straw mulch over the soil surface
produced more roots than those with grass, cultivation or herbicide soil man-
agement. Reckruhm (
,
) found more pear roots under mulch than under
grass.
