The
fertiliser requirements of an olive orchard are not complex. Traditional
fertilising has always been simply done with natural well rotted
manures and mulches. This method ensures that all nutrients
applied are readily usable by the trees. It also reduces
the possibility of over fertilising which can have detrimental
effects on the trees, the soil, and the underlying water table.
Olive
trees are 'natives' of the Mediterranean countries and therefore
they should be treated as such even when introduced into
far off lands such as Australia. They're similar in their cultural
needs to our native trees such as eucalypts. In light of
this, regular or large applications of chemical fertilisers may
do more harm than good. Controlled chemical fertilising can
produce good crops, however it must be carefully monitored to
ensure no damage is done.
There
are many manures which are perfectly suitable for olive orchards.
The one rule which must be kept in mind is that no matter
which manure you choose or have access to, it must be well
rotted before being put onto the orchard. Fresh manures
can burn the roots of the trees. For details on fertiliser
requirements at planting see OLIFAX - 3.
A
manure which we use as an example and recommend due to its well
rotted and balanced nature is the manure found in meat chicken
sheds. The floor of the shed is covered with a layer of sawdust
prior to the chickens arriving. The chickens then spend a number
of weeks manuring on and scratching around in this sawdust
as they grow. After one or two batches of the grown chickens are
removed, the well mixed sawdust and manure is removed from
the shed and heaped into piles. This product is ready to
be placed on the olive orchard. (NB. You cannot reproduce
this product simply by mixing one tonne of fresh sawdust with
one tonne of fresh chicken manure as both ingredients must
be well mixed and composted prior to reaching the trees).
Well
rotted manure from horses, cattle, pigs and sheep etc are also
quite suitable. Just remember the 'well rotted' rule. Due
to the relatively slow release of nutrients from manures into
the soil, they tend to keep the soils at healthy nutrient
levels throughout the season. One application of rotted manure
after harvesting and pruning is generally enough to get the tree
through until the following winter. Spread the manure 25mm (1
inch) deep over the total under-canopy area (ie. The area
in shade if the sun is directly above the tree). Leave about
100mm (4") clear around the trunk to remove any chance of
burning the tree. Ideally, the manure can be spread out as far
as 300mm (1ft) past the canopy because olive roots do extend further
than the canopy.
Chemical
fertilisers are often applied in a liquid state for ease of
application and speed of infiltration into the soil. Remember,
chemical fertilisers can be utilised efficiently in an olive orchard
but they must be carefully monitored to avoid excessive applications.
Chemical fertilisers are generally less expensive and easier
to apply than manures.
There
have been numerous accounts of growers overfertilising their olive
orchard by using the same quantities and strengths of chemical
fertilisers as they put on their citrus or stonefruit orchards.
Remember, olives are native trees and don't appreciate large
doses of chemical fertilisers.
One
detrimental effect of over fertilising is that it can lead to
excessive foliage growth which requires heavy, time-consuming
pruning to bring the tree back into balanced production. This
'growth effect' is something that can be read about in books but
is most easily learned through experimentation in your own
orchard.
Details
on the diagnosing and correcting of specific nutrient problems
can be found in the Californian Olive Production Manual.
(This can be bought through our office or directly, but more expensively,
from California).
