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Irrigation Fruit fi rmness from Fruit fi rmness after 1 week Fruit soluble solids content after Incidence of ‘over soft’
treatment cold store,19 Sep.(kgf) at 20°C, 26 Sep.(kgf) 1 week at20°C, 26 Sep.(%) fruit(%)
Full-irrigation 1.4 a 0.7 a 13.7 a 15 a
Half-irrigation 1.9 b 1.0 b 14.3 a 7 b
Quarter-irrigation 2.4 c 1.4 c 14.7 a 4 b
Table 3. Effects of irrigation treatments at a Gisborne Hayward orchard on fruit fi rmness after 24 weeks of cold storage at 0° and fruit attributes after one week of shelf
storage at 20°C (n=3 plots). Fruit were harvested on 4 April.
For a harvest date, means in a column with the same letter are not signifi cantly different at P=0.05 (LSD).
Fruit from this experiment had not fully
ripened by the time of reporting. Even after
24 weeks of cold-storage at 0°C followed
by 1 week at 20°C, fruit from almost all the
treatments were not at eating fi rmness and
none had reached their full soluble solids
content (SSC) potential. The difference
between harvest DM and SSC for fully ripe
Hayward kiwifruit should be between 2.7
and 3.0 units (Burdon et al. 2004). In our
trials, the differences were between 3.4
units (full-irrigation) and 4.0 units (quarterirrigation).
We could assume that fruit would
have ripened normally, if they had been
treated with ethylene gas. However, it would
be useful to confi rm that this would occur
and that fruit from defi cit-irrigated vines do
achieve improved eating qualities in any
future research.
ARE WATER DEFICITS FEASIBLE
AS A TOOL FOR KIWIFRUIT
GROWERS?
Using severe water defi cits to increase
kiwifruit dry matter would not be feasible
for kiwifruit growers, at least with the current
payment incentives for dry matter and size.
The fruit payment benefi ts that would have
been received this season for the increased
DM would have more than been offset
because:
1. Yield of Class 1 trays would have been
reduced, as more of the (smaller) fruit
would have been required to fi ll each
tray
2. The fruit size payment profi le would
have become less favourable, because
of the smaller fruit size
3. The KiwiStart payment would have
been reduced because of smaller fruit.
The management of soil water defi cit was
relatively crude in this study. We simply
reduced the irrigation volumes mid season
and waited for an outcome, relying on
orchard management to schedule irrigation
across the entire orchard. However, it is still
possible that the controlled use of mild
water defi cits, as part of a regulated water
defi cit (RDI) strategy, could be feasible in
some situations. On other crops such as
apple (Ebel et al. 1995) and peach
(Chalmers et al. 1981; Goldhammer et al.
2002), RDI strategies can successfully
target water stress to periods when fruit are
growing slowly and/or when active shoot
growth is occurring. For example, water
defi cits are often used in wine grapes to
reduce unnecessary vegetative growth (Dry
et al. 2001), which can increase fruit DM
and reduce pruning costs. The potential for
RDI strategies to benefi t Hayward vines
may be small with the current low-vigour
management systems. However, there may
be a greater ability for such strategies to
benefi t Hort16A, which usually displays a
vigorous growth fl ush over the summer
period between January and March.
Hort16A trials are currently underway in Te
Puke as part of a MAF Sustainable Farming
Fund (SFF) co-funded project (Project
TZ0736).
NZ KIWIFRUIT JOURNAL JANUARY / FEBRUARY 2008
11