Agriculture Reference
In-Depth Information
120
100
80
60
40
20
0
20
10
0
6 3 0
27
3
10 17
September
18
25
2
9
16
23 30
June
July
August
Figure 9.7
The effect of irrigation on apple fruit growth in a drought
year (1976) in England.
•
,trickle irrigated to provide full daily
potential transpiration requirement;
,unirrigated. Derived from
Goode
et al.
(1978a) with permission.
Apples grown at high altitude and under cool conditions tend to be more
elongated in shape (Greenhalgh and Godley,
; Eccher,
). This is com-
mercially important for 'Red Delicious'.
!
Irrigation in a dry season can have dramatic effects on fruit growth and final
fruit size at harvest (Figure
.
). Averaged over a number of years, Goode
et al
.
(
b) found that early irrigation, in June only, had no effect on mean fruit
size whereas late irrigation ( July to mid-September) increased this significantly
even though it also (slightly) increased the number of fruits harvested.
This effect of early versus late irrigation, together with the contrasting fruit
growth curves of irrigated and non-irrigated fruits shown in Figure
, sug-
gests that the effect of irrigation is on the cell expansion rather than the cell
division stage of fruit growth. In field trials like the above, a complicating
factor is that severe water stress seldom develops early in the season. How-
ever, early-season water stress imposed by regulated deficit irrigation under
controlled conditions has only a temporary effect on fruit growth, reversible
when irrigation is resumed (Behboudian and Mills,
.
). Fruits appear to be
able to osmoregulate to maintain growth under early-season deficit irrigation
conditions severe enough to inhibit vegetative growth (Chalmers
et al.
,
).
Whereas induced water deficits for the period from
days after full bloom
to harvest led to reduction in the weight of 'Braeburn' apples from
days
after full bloom and to smaller fruits at harvest, deficits starting at
days
after full bloom had no such effect (Mills
et al.
,
). The imposed deficits
