The main factors to take into account that affect the production of olive groves are the light and water which are essential in the design of a plantation, for a short period without production and making the most of machinery in cultivation operations of olive farming. Olive plantations can be in: contours, terraces or terraces (with minimal erosion and water loss as possible), or on ridges where soils have a very good surface profile for the crop, but with drainage problems.
At the time of planting olive trees the first thing to do is make a design (shape and placement in which you will plant olive trees). Later mark the spot with a stake or other means where you want to make the hole to put the olive tree (the size of these holes must be proportional to the size of the root ball of the olive). These holes can be made with diggers, or by hand, depending on terrain and the season in which you do it. The olive should be buried in the hole at a maximum of 5 cm. Then when we cover the hole must tread the soil to avoid air pockets. These olive trees have to be watered at least 50 litres per foot.
After the preparation of the site, before planting the olive trees, remove the roots of any trees or shrubs, build terracing, level the land etc. Once the land is ready its advisable to plant cereales or pulses for one or two years to eliminate the roots completely, so that there will be no problems with the olive trees. For the proper destruction of the weeds it may be necessary to plough in deep. Afterwards you should plough again all of the earth for the good growth of the olive trees that you're going to plant. In the last ploughing you do you need to distribute phosphorous and potassium based fertilisers that will be needed by the tree for the first few years of growth. It's recommendable that before you use the fertilisers, you analyse the soil.
When planting olive trees we must condition the land, plough it, it is also advisable to use fertilisers.
The number of olive trees per hectare depends on the areas, the crop (rainfed or irrigated) and the type of olive tree that we will grow (if it has one foot or two). When we plant trees in a field we must consider the circumstances surrounding it: the type of soil (if rich or poor, deep or shallow, etc..), the amount of rainfall (the higher the amount the more olive trees we can plant), and the proper order of olive trees (with gaps of at least 7 meters between each row, to allow machining on the plantation). Another point to consider is the orientation of the rows of olive trees, which in the case of rectangular has to be north-south for better lighting. The best time to cultivate the olive tree is in autumn or spring when there is no risk of frost.
Cultivation systems that can be used in the rainfed orchards are:
- Tillage: to preserve the land without any vegetation for the duration of the year, is the most used. The instruments used to perform the tasks of land clearing are cultivators and vibrocultors, although these tasks are among the most superficial. The order in which they perform work throughout the year will be:
1.- After harvesting the olives, preparing the land so that the water has better access.
2.- Before the arrival of summer you need to do between two and four laps to remove the weeds (depending on the rain that falls), thus preparing the land for the summer.
3.- In the summer the land tillage is much lighter, with the use of tine harrows.
4.- The only thing left to do is condition the plantation for the harvesting process. This consists in solidifying the ground, with use of a roller, for collecting olives at the lowest possible cost. The only problems with this method are that the soil generates erosion damage, and it causes cracks in the roots producing an imbalance in the development and production of olive oil.
- No tillage with bare soil: this technique is that the soil is stripped of weeds throughout the year, with the use of herbicides. These must vary with the age in which they apply: if applied in autumn, mid autumn after the first rains, or in spring (where translocation herbicides are used to eliminate perennial weeds).
When we go to prepare a schedule for the maintenance of the grounds we must have in mind which herbicide to use; if it persists and is well absorbed, and does the job effectively (residual, contact, or translocated).
The only problems that occur in cultivation with zero tillage are the alteration of the flora to weed species that could not be controlled effectively with a residual herbicide, and deep trenches that are produced by erosion waters where there is the natural outlet.
- Reduced tillage: in this system work of different intensity is combined with the application of herbicides under the canopy of olive trees, an area that remains uncut throughout the year. Presents some variations:
1.- Semi-tillage: In this type of tillage residual herbicides are used and applied under the olive tree, with cross-tillage in the middle of the rows of trees. This technique reduces costs and enhances crop production capacity relative to conventional tillage.
2.- Minimum tillage: in this type of tillage residual herbicides are used throughout the plantation. And every year some work must be done in the middle of the rows of the trees, but very light work, when we see that the outer layer is dry (this task is performed with a vibrocultor).
- Olive tree cultivation with covering: allows us to resolve, in a more effective manner, the erosion problem. There are four types of coverage:
1.- Cultivation with inert cover: this is creating a cover with leaves that have fallen, and pruning cuts, all well chopped, and well distributed across the surface. The cost is not high and it holds well on the ground. Occasionally we may also use small stones, when the grove is irrigated.
2.- Cultivation with living vegetation cover: this cover is created during the rainy season. In late winter, when you have enough coverage you water it and leave it on the ground to prevent erosion and reduce water loss by evaporation during the spring. The harvest can be done in several ways:
- Using bush cutters or mowers (mechanical mowing)
- With the use of contact or translocated herbicides (chemical mowing), which is the most desirable because it is the simplest, prevents regrowth, and is the cheapest.
- With sheep grazing (natural mowing)
3.- Live crop of barley cover: consists in sowing in the autumn a cereal (barley) in the rows of the plantation. The advantages of this type of culture are: the seed is fairly inexpensive, it has a high tillering capacity, it's a rustic species of winter growth, it is easily established, and economic when it comes to chemical mowing. With this crop it is irrigated on entering in the autumn, with nitrogen (50 kg per hectare), and left to grow in the winter. The chemical mowing takes place in March (with a herbicide translocation). The straw is left on the ground, with the only drawback being that a fire could occur.
4.- Live crop of legumes (vegetables) cover: the legume is managed like barley, but is better as it can take up a lot of nitrogen, which is highly favorable for the cultivation of the olive tree. It's also better suited to mechanical harvest, because they rarely re-sprout, and there is less risk of fire. The only drawbacks are the low retention in the soil (as it does not safeguard us from erosion), and the difficulty of mowing with the use herbicides.
In order to choose a good olive cultivation system you should consider several points: the availability of water in the soil (depending on the infiltration and evaporation), soil erosion, production, fertilization, costs of cultivation, planting temperatures, the amount of pests and diseases that could affect things, the wildlife and microorganisms in the soil and the widelife in the olive grove.
To make a good olive crop the infiltration of water and temperature must be taken into account.
The cultivation of soil must meet the following requirements: an optimal use of available water, a perfect land use, keep trying to reduce erosion as much as possible, facilitate the work of cultivation, and keep the cost down.
Some of the care that must be done in the cultivation of olive trees after planting are:
- Pruning: a must for the condition of the trees in the climate and to increase productivity. The main objectives of pruning are: to stabilise the vegetation with fruit production, reduce non-productive phases, increase the productivity of olive trees, delay it's death and save ground water. The pruning of olive trees can be done at the end of the harvest; the making of green table olives is done between November and December, and the black ones in February and March. But generally it can be done from autumn until spring, but in areas where there is risk of frost it should be delayed. There are three main types of olive tree pruning:
> Pruning: have, as aims, the formation of the structure, crown and root system of olive trees to benefit its growth in the early years, to facilitate cultivation, the growth of its branches and above all the harvest. So from when you plant until the arrival of next summer, you will have to remove shoots that come out on the lower trunk. Pruning to regenerate branches is carried out every two years, but severe pruning is not advisable. The method used in the pruning of olive trees is the 'free cup'. Tree pruning is done after one year, when the tree has reached a height of 60 to 80 cm. from the ground. In the first year of pruning, lateral branches should be done around the central shaft at a height of between 30 and 60 cm. from the ground. In the following years, pruning is much softer, where only the buds that are damaged or cross each other are removed. When the tree is already well developed, we must choose between 3 and 5 branches (around the central axis), with a distance between them from 20 to 30 cm, so that the olive tree will take a spherical shape.
Regeneration pruning of the trees should be done every two years, severe pruning is little recommended.
In the intensive cultivation of olive trees it is preferable to carry out short pruning (pruning cuts or shrub), where you should not do any pruning until the first 5 or 6 years and then only remove the shoots that are growing weaker and the branches that grow more than three meters. Some advantages of this pruning is that the production phase of the olive tree begins earlier, which gives more production of olives, and is cheaper (with reference to personal spending, and there is no need to use ladders).
> Pruning for production: what is intended with this pruning is that the productive branches forming fruits, without affecting in any way the structural branches of olive trees, get a good light and keep active in the productive area. In intensive farming it's not as effective as they do not get the necessary light (where the production area is restricted to the upper parts).
During the production stage of the olive tree pruning is advised every year, but not too abrupt in order to phase out wilted branches (thus avoiding the appearance of short or dense shoots) and this will also improve the length of the outbreaks of shoots, and ensure that the light reaches the entire production area. In areas where soils are dry, with low humidity or infertile, the olive tree pruning should be severe, and will save water and nutrients, which may be used in the further growth of the olives. However, in fruitful soil, severe pruning is not needed, as they have sufficient water and nutrients.
> Renewal pruning: it's to encourage new growth and to strengthen the oldest olive trees. One of the characteristics of the olive tree which has a long life, is it's ability to produce new shoots easily. Another way of rejuvenating the olive trees is to cut the trunk at the point where it branches, or cutting it low down. To make a renewal, but only partial, early branches should be pruned at the height you want.
- Irrigation: The olive tree has small leaves that have a protective, hairy layer on the lower surface area, which reduces water loss, so that the cultivation can be done in areas where other trees would not survive. 95% of the olive groves are dryland (non-irrigated land which receives little rainfall), but production increases with the use of irrigation. Irrigation should be used when precipitation falls below 800 mm. When it only rains in the winter (missing moisture in spring and autumn periods) and when the soil is sandy or has gravel (with little water retention) The most suitable irrigation for the olive grove is drip irrigation (each olive tree is watered between 1800 and 1900 liters per year, spread over the months of April, May, June, July, August and September).
- Fertilization: it is hardly necessary in the first four years of cultivation in more or less fertile soils. In the case of fertilizer use different substances can be used, such as:
1.- Nitrogen is one of the most crucial components in the growth of the trees. The benefits of Nitrogen become more obvious when used in not very fertile lands. Depending on the type of soil, the amount of nitrogen to use is different, depending on moisture and soil fertility. In plantations with little amount of trees the proper amount of nitrogen is between 500 and 1,500 grams, but in olive groves where there is more density of olive trees (if you have more than 100 trees per hectare) between 50 and 150 kg is recommended per hectare.
In rainfed areas the amount of nitrogen varies depending on rainfall and soil moisture. If annual rainfall does not reach 400mm, apply 100 g per olive tree, per 100 mm of rain. If rainfall ranges between 400 and 700 mm, it should be increased in a manner proportional to 1,500 gr. per tree. And if the annual rainfall exceeds 700 mm. (olive crops irrigated) adding nitrogen will depend on soil fertility, reaching up to 1,500 gr. per tree.
To ensure that nitrogen has acted correctly (and if otherwise, in order to correct the amount added) it can be verified in two ways: first by observing the length of the new vegetation, and if it becomes apparent that not enough has grown you can increase the amount of nitrogen (in cases not caused by disease, damaged roots, and so on.) The second is to analyze the olive leaves. The amount of nitrogen in the leaves should be between 1.6 and 1.8% in the winter.
2.- Phosphorus: in trees in general the lack of phosphorus is not usually frequent, so its use is not indispensable. It is not necessary in the olive trees that have been provided with phosphates for several years, nor in the olive trees where low amounts of phosphate have been added for the low soil moisture. In the case of the land having a fair amount of calcium carbonate or acidic phosphate fertilisers if it might be necessary.
As with nitrogen, a lack of phosphate can be seen by looking at the leaves. If the nutrient count is between 0.09 and 0.10% in the winter phosphate fertilizer should be added. This could also confirm if there are shortages of phosphate in general chlorosis of the leaves. Although this could also occur for other reasons such as lack of nitrogen, so the most reliable analysis is that of the leaves.
3.- Potassium: during the olive harvest and pruning, the soil loses a good proportion of potassium, thus it is a substance needed by the olive tree. Therefore the use of potassium fertilizer enhances production capacity and the quality of the crop. The use of potassium should be combined with nitrogen. In groves where potassium hasn't been used before it's best to double the potassium to nitrogen. And over time the amount of potassium will adjust, until it equals that of the nitrogen. It is also beneficial when the olive tree is in the period of high production that you increase the potassium dose to make up for the amount used in production. An analysis of olive leaves, will indicate if potassium fertilization is needed, or whether to vary the amount of potassium.
Fertilisers, such as nitrogen, phosphorus or potassium stimulate the production of the olive trees.
- Plant care: there are pests and diseases that attack the olive trees at an early age which may slow their development, and even cause death eg. mites or Peacock spot (Cycloconium oleaginum). Therefore we must keep an eye on the olive tree to see if it has a condition, what kind of disease is, and its possible solutions.
- Soil Maintenance: previously tillage was used to remove the weeds, which created many problems of erosion and lost a lot of soil fertilization. With the practice of no-tillage, using herbicides, you get a higher performance in addition to lower costs, but its drawback is that pits are formed by the flow of rainwater. The most recommended nowadays is minimum tillage, where you tillage in a very superficial manner, to break the crust. According to whether the plantation is new or well developed, the weeds should be controlled in one way or another.
> In new plantations: during the early years of the olive tree is when you will have more problems with weeds damaging production. And as the olive tree grows, its own shadow blocks the light and greatly reduces the spread of weeds. Some ways to control these weeds are:
- Cultivation: sometimes in the early years, farmers prefer not to use herbicides on their plantations. Therefore they tend to remove the weeds with a hoe, and clear up everything that is around the olive tree, this has to be done more than once at least in spring and summer. It's also good to plough all the land that lies between the olive trees, where you can use discs, cultivators and mowers. We must try to remove these weeds while they are still at the stage of seed formation, and so are less developed and more easily removed. The tools we use must be suitable, so as to prevent any damage to the tree (eg. not having a deep cut so it isn't able to damage the roots of the trees).
- Cover crops: to curb weed growth it is suitable to plant between rows of olive trees. What to plant depends on the area where you are, but don't ever plant anything that could compete with olive trees, you could plant wheat, oats, rye or barley.
- Pajuzo: the weeds that grow among the trees can be prevented by placing straw on the soil, it can be organic or synthetic. But it has to put down after clearing the weeds, so that all light is removed and they can not grow back. In addition this produces moisture in the soil which favors the trees.
- Herbicides: herbicides have to be applied before the olive trees produce fruit. The first thing you do is put herbicide around each tree or only on one side of the row of trees. It can also be used to kill weeds when they have already sprouted, controlling them.
Herbicides are a technique to eliminate the weeds that appear in the land where the olive trees are growing.
> In developed plantations: for an olive grove to be considered developed is has to be at least 3 or 4 years old. With this many years they can better tolerate herbicides, making it easier to kill weeds. They are normally controlled by mowing and putting herbicide around each olive tree, or on one side of the row of olive trees.
- Cultivation: in developed olive groves the weeds can be controlled, every two years or every year. Cultivation cuts and damages the roots of the trees, so that soil nutrients are depleted sooner. Be very careful when using this method.
- Burning: with this you can control the weeds of young olive trees. Burning is only effective where weeds are newly grown. The burning can be done with a single flame at the base of the olive tree, or else at various points to burn the weeds among the olive trees. Also used to destroy the fertile seeds with heat. This method is not recommended in young olive trees as it can damage the bark. Nor should we use it where there is dry vegetation, dead or leaves the area around the tree that could ignite easily.
- Straw: this must be replaced constantly as otherwise it rots and turns everything into a perfect area for weed growth.
- Herbicides: these can be used in several ways; alone, in combination with other herbicides, in a dose (in autumn) in two doses (in the fall and spring), or in winter. This herbicide is called pre-emergent. The post-emergent can be applied later to prolong the period of weed control in summer. Herbicides should be applied, for security, by spray on to the soil or the foliage of the weeds, not directly to the leaves of the trees.
- Nutrition: usually only performed with nitrogen (with 4% urea, from 0.5 to 1 kg per tree). It can also be done with potassium, but their response is later (add between 300 and 400 grams per tree).
- Planting scheme: this will depend on the cultivation that you are going to use, intensive or non-intensive. If intensive with fertile soil that has plenty of water, olive trees are planted at a density of between 200 and 300 trees per hectare. In areas where the soil is less fertile and it receives less rainfall, planting density is reduced.
In the land where there is little rain the density of olive plantation must be decreased.
In rainfed plantations do not go over 300 olive trees per hectare. And the way to plant is rectangular (7x5 or 6x4) In general there are two paths of plantation: the traditional, in which the separation is 7 x 7 m, 6 x 8, 8 x 8 or 10 x 10 m according to the area, and dynamic, which are planted at a separation of 5 x 6 m. or 6 x 6 m. Also can be planted in a square and a diamond shape.