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Thirsty vines can give tasty fruit, but at a cost…
Mike Currie, HortResearch - Mt Albert, Steve Green, HortResearch - Palmerston North
Philip Martin and Nicola Currie, HortResearch - Te Puke
Allowing Hayward vines in Gisborne to develop severe water stress
in 2007 gave a massive improvement in dry matter, but with a
corresponding loss of fruit size and yield, which would have reduced
fi nancial returns. However, over-watering vines should also be
avoided because this can result in root health issues as well as
costs to the environment.
WATER STRESS AND TASTE
A wide body of published information on other fruit crops (e.g.
grape, peach, apple) suggests that regulated defi cit irrigation can
elevate dry matter (DM) levels in fruit, without necessarily affecting
yields (FAO 2002). Historic research conducted on potted Hayward
kiwifruit vines suggested that mild water stress during summer can
increase dry matter of the fruit (Miller et al. 1998). While there are
also many anecdotal reports suggesting that fruit from waterstressed
fi eld grown vines have better fl avour, the feasibility of this
response had not been confi rmed with fi eld trials.
Some growers also believe that late-season rainfall reduces fruit
DM, by diluting fruit constituents. Recent studies at Te Puke
suggested these effects may be small (Currie & Nicholls 2006),
although impacts in very dry conditions were not tested at that
time.
WATER STRESS AND FRUIT GROWTH
The sensitivity of fruit growth to soil water availability has been well
documented for kiwifruit (Judd et al. 1989; Smith & Buwalda
1994). Inadequate soil moisture can result in signifi cantly smaller
fruit, particularly early in the growing season when the fruit are in
their most rapid phase of growth (Figure 1).
Irrigation is not generally considered a key input on many Bay of
Plenty orchards, because the soils are deep and they have suffi cient
water-holding capacity to limit the effects of summer drought.
However, on the lighter pumice soils in eastern Bay of Plenty, very
low available moisture reserves are held in the soil and in most
seasons there are periods when vines are likely to experience
moisture stress. In other parts of the country such as Kerikeri,
Gisborne and Nelson, rainfall can be lower and the soils are
shallower so there is a greater likelihood of water stress developing
during summer.
Figure 1. Early kiwifruit growth is very sensitive to water stress
2007 – A VERY DRY SUMMER
This past growing season was one of the driest on record. In
Gisborne, the period between January and April 2007 was the third
driest it has been in the last 36 years and there was insuffi cient
rainfall to meet vine needs (Table 1). This made 2007 an excellent
year to investigate how water defi cits could affect fruit dry matter
and yields in fi eld conditions. It would be fair to say that the research
team were very pleased with their good fortune – normally
conducting any water stress research in New Zealand will guarantee
persistently heavy rainfall for the entire season!
2007 TRIALS IN GISBORNE
At a commercial Hayward orchard in Gisborne (Figure 2), a trial was
initiated where vines received one of three treatments:
NZ KIWIFRUIT JOURNAL JANUARY / FEBRUARY 2008
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