Olive Agencies Information Services


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.

* Soil pH Test Kits are available through Olive Agencies. They are a simple yet accurate kit which quickly tests the pH of your soils. The kit will be a valuable asset to monitoring your orchard for years to come.