Olives have their origins in the Mediterranean basin where they are generally well adapted to the climate and soils.
They have been widely cultivated there for at least 6,000 years. In New Zealand, the small (1,200 ha) but fast-expanding
olive industry has established groves all the way from Northland to Central Otago. These have been planted on a wide
range of soil types ranging from sand to clays.
For the most part, New Zealand olive groves enjoy a mild maritime climate with a relatively evenly-distributed rainfall
pattern. The climate is quite different from the hot dry summers and cool wet winters of a true Mediterranean climate.
Although olives have shallow root systems, they are quite tolerant of a range of soil types and they very tolerant of
drought. However, they are not tolerant of poor drainage. As a result they will suffer wet-feet problems on heavier
soils - especially in the New Zealand climate.
In New Zealand, olive trees tend to excessive vigour. It is therefore preferable to establish groves on the more
'stony' soils - similar to the soils preferred by winegrowers for the same reasons. While with mature trees the
reduced vegetative growth achieved with these soils is desirable, it is a different matter during establishment.
Here, the young olive trees require good access to water and nutrients in the upper soil layers to encourage
establishment, good health and vigorous growth.
As with winegrapes and kiwifruit, gypsum can be usefully
applied at planting to correct local soil-quality problems caused by 'contouring'. This practice, designed to assist with
machine access to previously uneven ground, exposes strips of subsoil to present a surface that suffers compaction, low
nutrient status and low organic matter. Together with deep ripping and the incorporation of organic matter, gypsum will
help to remedy these problems and so reduce establishment losses, encourage early tree growth and early fruit bearing.
Olives prefer a soil pH in the range 7-8 but they will grow on calcareous soils (pH above 8.0). Depending on variety,
olives will tolerate a pH range from 5.5 to 8.5 but optimal plant health and growth are obtained under the preferred
conditions.
Gypsum is a well-known and effective way to remedy many of these adverse soil conditions, especially in heavy soils with
high clay contents. Gypsum encourages the formation of a better soil structure with better retention of organic matter
resulting in better drainage. Moreover, gypsum also helps to reduce wind and water erosion that can be a problem in
freshly prepared and exposed soils during the early years of establishment. Gypsum can also help with compaction problems.
To gain the best benefit:cost from gypsum in terms of soil remediation, it makes sense that the gypsum should be
distributed in line with an assessment of the severity of the soil problems. It should, therefore, be applied at the
highest densities (rates up to 4,000 kg/ha) in areas where soil problems are perceived to be worst and at lower
rates where they are less severe.
Olive trees, like other plants, require good mineral nutrition if they are to maintain high health and production. Free
draining, stony soils are easily leached and thus are commonly nutrient deficient. Used as a fertiliser, gypsum at 1,200
kg/ha is a good source of both calcium and sulphur.
