It
has been found that the addition of agricultural lime (calcium
carbonate) to many Australian soils, will improve the health,
growth and crop of olive trees.
Following
are a couple of statements that show the reason for this.
"The
optimal soil pH for olives is not known, although olives grow
poorly on soils with a pH above 8.5. Some California soils have
a pH higher than 7.0 and high levels of calcium. Olive
trees grow well in these calcareous soils." (Californian
Olive Production Manual, p.70)
"...This
variety has an average oil content of 22-24% when grown in Sfax
(Tunisia) whereas in the north this yield drops to 16% and even
13% on the infertile, calcium-poor soils of Cap Bon." (Olivae
No.61, April 1996)
It
is interesting to note that wherever olive trees are performing
at their very best, the pH of the soil will be found to
be somewhere between 7.0 and 8.0.
Acid
soils have a low pH reading and alkaline soils, suitable for olives,
have a higher pH reading. Acidic soils can be improved by the
addition of agricultural lime.
The
following are a few of the benefits you will gain by adding agricultural
lime to acidic soils. Our thanks goes to DML Aglime for much of
the information.
1.
Calcium is an important constituent of cell wall material,
adding strength and stability to the plant. Calcium deficiency
causes stunted growth in olive trees and also the development
of 'soft nose' where the fruit develops a rotten end thus making
it completely unfit for sale. 'Softnose' occurs when the
fruit begins to change colour from green through to black and
has occasionally been seen in Australia where the variety Sevillano
has been unable to get enough calcium.
2.
Lime corrects acidification. Soil acidification is part of
Australia's land degradation problem. As far back as 1989, the
CSIRO estimated that soil acidification was costing Australia
more than $300 million per year in reduced crop production.
That is something that we don't want the olive industry
to suffer.
3.
Adequate levels of lime in the soil will reduce Aluminium
and Manganese toxicities. The lower the soil pH, the more
readily these toxic elements are released into the soil
to adversely affect the health of growing plants.
4.
Fertiliser efficiency is improved when agricultural lime is
added to acid soils. Liming acid soils will increase the
uptake of nitrogen, phosphate, potash, sulphur, calcium, magnesium,
boron, copper, zinc and molybdenum.
5.
Beneficial soil bacteria are generally more prevalent in the
sweet alkaline soils rather than acid soils.
6.
Agricultural lime improves soil structure and promotes worm
activity. The addition of lime to most soils will improve their
friability, thus reducing crusting and clodding of heavy
soils.
7.
The composting of organic matter in the soil is significantly
improved, thus contributing to good soil composition and less
need for ongoing tillage.
How
Much Lime?
Before
I plant my olives, how do I know if my soil needs lime? Well firstly,
don't guess. Take a soil sample to be tested by a reputable soil
laboratory. Because the olive tree is a relatively shallow
rooting tree, scrape away the top 100mm (4") of soil
which contains a lot of organic matter and discard it. Then collect
about half a kilo of soil from the 100-200mm (4"-8")
layer. Collect a second sample at around 600mm (2ft) deep.
Take
the soil samples to the testing laboratory. You will often find
that the top sample will have a lower pH than the bottom
sample. This means that by deep ripping to open up the soil to
a depth of around 600-700mm (2ft - 2ft 6") before planting
your olives, the lower layer with a higher pH will be mixed with
the top layer with a lower pH, thus 'leveling' the pH levels.
For
olives, if the mixing of the two soil levels still would not bring
the pH level to a minimum of 7.0, then the addition of lime
into the soil will be very beneficial.
For
maximum benefit, the lime should be deep ripped into the soil
to a depth of at least 600mm (2ft). Your soil laboratory
or fertiliser supplier will be able to suggest how much lime will
be required to raise the pH to between 7.0 and 8.0. As a
very rough rule-of-thumb, the following rates will apply.
In
sandy loam, the approximate amount of lime required to
raise the pH of your olive ground to a depth of 600mm (2ft)
by one pH unit (eg. to go from 6.5 to 7.5) would be 1.5
to 2.0 tonnes per hectare. Remember, this is not just a
shallow dressing for shallow rooted vegetables, but a deep ripped
application to cover the full depth of the olive roots as
they mature over many years. This 1.5 to 2.0 tonnes per
hectare would be applied in a 3 metre (10ft) wide band down
the row lines and very thoroughly deep ripped in to a depth
of 600mm (2ft) and a width of 3-4 metres (10-13ft). An unlimed
grass strip between the rows would therefore be left unripped.
If you choose to rip or lime the entire paddock, more lime
will be needed.
Be
very careful ripping the entire paddock if there is a chance of
causing excessive erosion problems.
In
heavier clay soils, you will probably need at least twice
as much lime to raise the pH level by one unit.
Lime
is relatively inexpensive and if you can afford to use it, your
investment will bring excellent returns over many years.
