Much of New Zealand's kiwifruit is grown in the Bay of Plenty where the soils are generally deep and free draining, and
do not require the soil remediative properties of gypsum. However, many blocks were extensively 'contoured' prior to
planting to remove the worst topographical irregularities and so allow better access for machinery. Contouring has
sometimes created strips where deeper subsoil layers have been exposed. Vines in these strips can suffer from poor
drainage, low soil organic content and compaction. Gypsum applications will help here.
To a lesser extent, kiwifruit are grown in a number of other regions in New Zealand and on a wide range of soil types. In
general, they yield best on soils that are well drained, and thus not prone to waterlogging, and also not likely to dry
out too quickly in the summer. The application of gypsum in orchards with the heavier soils, especially those with poorly
drained soils, will improve fruit yield and quality significantly through its beneficial effects on soil structure.
The improvement in soil structure obtained following the addition of gypsum is also likely to improve the general health
of kiwifruit vines and to reduce the chances of their suffering 'wet feet' related diseases.
There is still some debate concerning the role played by fruit calcium deficit in predisposing kiwifruit to postharvest
disorders such as premature softening. Certainly 'Hayward' (ZESPRI™ green) and the new golden-fleshed kiwifruit (ZESPRI™ gold)
have higher levels of fruit calcium than apples and, indeed, many other fruitcrop species. However, more research is
required before clear conclusions can be reached regarding the relationship between kiwifruit calcium and kiwifruit
quality.
Unless soils are notably calcium deficient (some are), improving the calcium status of the fruit is unlikely to be simply
a matter of putting more calcium on to the ground. The reason for this is that low fruit calcium status has more to do
with the calcium transport physiology of the plant, than with calcium uptake by the vine. This aspect of kiwifruit vine
physiology is not unlike that of apples.
The various
apples cultivars are all of
the same species (
Malus domestica) and the familiar ones are mostly closely related to one another (thus, the
parents of 'Pacific Rose™' are 'Gala' and 'Splendour'; the parents of 'Gala' are 'Golden Delicious' and 'Kidd's
Orange'; and the parents of 'Kidd's Orange' are 'Delicious' and 'Cox's Orange Pippin').
In sharp contrast to this, the new kiwifruit
now coming into production are genetically much more diverse belonging to several, quite distinct, species - 'Hayward'
(ZESPRI™green) is Actinidia deliciosa, 'Hort16A' (ZESPRI™gold) is Actinidia chinensis and 'Arguta' is
Actinidia arguta.
Because of their newness, relatively little is known about the individual calcium requirements of these new kiwifruit.
Therefore, in the certain knowledge that most fruitcrop species suffer from specific calcium-deficiency disorders and,
in the absence of more detailed information on the new kiwifruit species, it makes extremely good sense to maintain
the highest possible soil-calcium levels when growing them. Heavy gypsum applications are an excellent way to do this.
