We want our olive trees to bear fruit in the next production year. For this, the plants must be fertilized. This must be done in late winter or early spring at the latest. If there is sufficient rain, this will give the fertilizer time to be assimilated. It may also necessary to fertilize the leaves and canopy of the plants to administer nitrogen. This, however, will, perhaps, be done in June.
We fertilize because olive trees consume a certain amount of nutrients in the soil. In order to ensure that it will also be able to produce next, we have to somehow return a more or less equal amount of these elements to the soil.
Fertilization is a complex practice because the soil is not an inert substrate, but a very complex environment in which many factors interact.
A fertilized plant is vigorous and best able to fend off the attacks of parasites, regularly carry out its biological cycle and produce quality fruit.
What do our olive trees need? Here are the nutrients
The main nutrients that are administered are nitrogen (N), phosphorus (P) and potassium (K); other nutrients are boron and magnesium. These are the symbols that we can read on the bags of fertilizer that we buy. On the 25-kg bags, there are numbers, such as 20-10-10, which mean that every 100 kg of fertilizer will have 20 kg of nitrogen (N), 10 of phosphorus (P) and 10 kg of potassium (K).
Nitrogen mainly influences growth and, thus, the vigour of the plant; it stimulates the growth of new shoots and flowers and, for this reason, it is indicated for poor soil or plants that have been stressed or abandoned for some time.
Phosphorus influences the biological cycle of the plant in general and its lack is revealed by a lack of development of the plant and scarcity of fruit. For this reason, it should only be administered in high doses if you are sure that the soil needs it.
Potassium is critical for good fruiting and also helps balance the stresses of high temperatures by regulating the flow of water in the plant.
Other less important elements (micro-nutrients) are magnesium and boron.
Costs (net of VAT)
|Purchase cost of the fertilizer
300 kg TIMAGOLD 10/8/18s+Micro ATB Plus
3 kg Caffaro Blue Copper
|Cost of labour (2 hours)||
| TOTAL (NET OF VAT) 399,31
The soil is a complex system: it is like a sponge through which liquids move that contain nutrients available to the roots of plants through specific channels. The availability of nutrients is, however, linked to the microbial activity of the soil. For this reason, organic matter resulting from the breakdown of animal and vegetable substances is also necessary. Moreover, organic matter in the soil improves its structure and ability to retain water.
For this reason, in addition to the elements listed, it is a good idea to use an organic base: to be clear, the classic manure!!!
Calculating the exact amount of fertilizer to use requires a soil analysis by an equipped laboratory (see the appendix).
The analysis reveals any deficiencies in the nature of the soil. It also clarifies the type of terrain, i.e., whether there is a predominance of sand, silt or clay. You don’t need to be a great geologist, but those who work in the country need to know the details of the soil. In the Province of Imperia, the soil is generally a limestone matrix with a prevalence of clays. This is the case of our olive grove. In addition, you need to know the basic pH (pH is a measurement of the acidic or basic reaction of the soil). In a purely theoretical way, there is a rule of thumb for the quantity of elements to return to the soil, which is 3 kg of nitrogen, 0.6 kg of phosphorus and 3 kg of potassium for each 100 kg of olives produced.
A small note: in general, the fertilizer should be buried to become immediately available to the plants. This is because, if the spring rains are scarce, there is the risk that it will “break down” quickly in contact with air and light. The soil should be turned to a depth of 20-30 cm, especially in the case of fertilizer based on phosphorus and potassium.
In the past, the soil of olive groves was thoroughly hoed and weeded with harrows: this eliminates weeds and favours the penetration of the fertilizer.
How do you fertilize?
Fertilizer is distributed in the section of soil beyond the projection of the canopy, where the majority of the roots have developed.
It is possible to fertilize the leaves using suitable equipment: liquid fertilizers are distributed on the leaves and readily assimilated through the circulation of the sap. This fertilizer is integrated with that on the ground in the pre-flowering to provide boron (which promotes and stimulates pollination) and in the summer in with olive fruit fly treatments.
Since our olive grove is in good growth condition and productive condition, we decided to distribute a fertilizer primarily consisting of potassium to further enhance the production of fruit and its quality. We will distribute approximately two kilograms per plant, taking care to place it on the projections of the canopy and hoping for favourable rain.
As always in the country, climatic information has a decisive weight.
Nuggets of history
A complete history of the fertilization of olive groves would require pages and pages. Two striking observations should suffice.
For example, in the Taggia countryside, and other places, there very of Taggia and not only, for example, there are very conspicuous late medieval towers. They certainly defended the dense olive groves but were also called “dovecote towers”. They housed colonies of doves whose droppings provided “colombina”: a highly valued fertilizer to for feeding the olive trees.
In Western Liguria, various parishes, such as San Lorenzo al Mare, used to sell colombina to finance the maintenance and restoration of the church.
In Liguria, an exception amount of attention is paid to the need for fertilization. But the practices of the past were different. The most popular was undoubtedly that of burying wool rags at the roots of trees. Incredibly, they are still found when tilling the soil. At the beginning of the 19th century, careful French analysts noted that the rags often came from the wool-processing area around Florence: the same area that used Ligurian olive oil to soften the newly-sheared wool. In this way a commercial and production circle was closed.
At the end of the 19th century, there was also a growing trend to use valuable guano from Peru: some made a fortune in this trade, replacing the “horn filings” from the slaughterhouse that were often used locally.