Spain

An European example to combat desertification:
Vegetation cover to improve olive harvests

spain
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Region Europe
Capital Madrid
Surface area 505,992 km2
Population 43,379,000 inhab.
Population density 86 inhab./km2
Infant mortality rate (per thousand births) 5
Fertility rate (births per woman) 1.3
Population growth rate (per annum) 1.1 %
Life expectancy (female-male) 83 – 76 years
Average temperatures (min./max.) 9.7 / 19.5 ºC
Forest area 29 %

Introduction

Europe is also threatened by desertification. Countries of the Mediterranean basin are the principal victims of a form of desertification afflicted by the effects of erosion. This problem is highlighted in the case study on olive cropping in Spain.
It is estimated that one third of the agricultural surface in the Mediterranean region is affected by land degradation. In Spain, it is largely the southern regions that are affected.
The moving and sparse soils on the steep slopes of the cultivated lands coupled with the semi-arid Mediterranean climate comprising irregular rains and seasonal droughts provide ideal conditions for erosion and desertification. Poor natural resource management further compounds these conditions. Water is the principal cause of (hydraulic) erosion even though wind erosion, caused by violent sweeping winds, can play a significant role. Generally, soil degradation by hydraulic or wind erosion represents a serious threat to both agriculture and forestry and to the environment of the Mediterranean rim.

Olive crops

The following example shows how ill adapted agro-forestry practices, such as traditional olive cropping in Andalousia, can ruin soil by erosion.
Soil degradation is indeed much more pronounced for olive tree cultivation than for the cultivation of cereals, sunflowers, or even grazing areas. According to official estimates, more than 80 tons of soil per hectare is lost every year in Andalusian olive tree plantations.
These losses are greater than the regenerative capacity of the soil. Furthermore, residues of chemical fertilizers may infiltrate and pollute the superficial layers of groundwater sources.

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1. Vegetation cover of shrub trees protects the soil between the olive trees.
© Asociación española agricultura de conservación

badCauses and effects of erosion

The Mediterranean climate is characterized by periods of drought alternating with violent rainfall during brief time periods. The hard, cracked soil makes it difficult for the rainwater to seep into lower levels. In addition, the steep topography of the cultivated lands tends to result in the downward flow of surface water.

Erosion occurs by the action of violent rains that disintegrate the soil when heavy rain flow downward along the slope. This causes earth particles to be torn away from the ground forming mudslides that scrape the soil still further. The hilly character of Andalusia accentuates this double process of erosion. In this way, a large amount of arable land is lost after each downpour.

The traditional ploughing system, commonly used in agriculture, generates most soil losses. In the dry regions, hard superficial layers of earth are formed after ploughing. The soil structure disintegrates when this upper layer breaks up, forming numerous fissures through which water escapes without being retained by the clay layer.

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2. Land eroded by violent rainfall.
© Asociación española agricultura de conservación

goodPossible solutions

The solutions to combat erosion therefore consist of using agricultural practices that curb the disintegration of the soil, favour water percolation and reduce the speed of water flow throughout the area of cultivation.

Therefore, discontinuing ploughing techniques could essentially halt the phenomenon of erosion and with time, the ground could become firmer (reducing disaggregation or disintegration of the soil) to better tolerate the impact of heavy rainfall without weathering.
However, it cannot be said that discontinuing ploughing in certain areas alone is enough to combat erosion particularly on the steeper slopes, since the natural flow of water as well as the effect of heavy rainfall would continue to erode the soil.

bladVegetation cover

The International University of Andalusia recommended a particularly effective method to prevent erosion with the formation of vegetation cover on the arable land. In traditional olive plantations, the bare soil is eroded between the trees, whereas with this method, low shrubs are planted between the olive trees to help retain the soil and protect them from erosion. Most of the scientists who participated in the study agree that the layer of low vegetation cover is the most effective method to combat erosion.

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3. Olive plantations without vegetation cover.
© Universidad de Andalucía
4. Olive plantations with vegetation cover.
© Universidad de Andalucía

Vegetation cover has multiple functions:

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5. Stages in the construction of vegetation cover.
© Universidad de Andalucía

Soil management systems applying the technique of vegetation cover have been adapted and developed for olive tree plantations on 50,000 hectares of land across Spain. This system has indeed proved to be very effective in combating erosion. The investment and agricultural education departments of the Andalusian government decided to spread the knowledge of this new agricultural technique to other regions.

As well as combating erosion, the combined effects of olive tree plantations and vegetation cover are advantageous to agricultural ecosystems, and a rise in biological diversity has been observed. Productivity is enhanced compared with traditional olive tree ploughing techniques and there is a rise in nutrients in the deeper soil layers. The vegetation cover provides a good deal of organic matter that is very beneficial to the olive tree ecosystem.
Cereals or pulses such as soy or beans and even weeds can be planted to form vegetation cover. It is recommended to use species that grow fast, propagate naturally and have a superficial root system.

The only vital condition to be met in order to obtain satisfactory results is to prevent competition for water and nutrients between the olive tree plantations and the vegetation cover. To achieve this, it is important to interrupt the growth of the vegetation cover by chemical or mechanical means: by properly applying herbicide treatment or pulling out the plants regularly. This ensures that the area directly under the tree is free from vegetation, which facilitates the harvesting of the olives (picture 5.).

Studies conducted over a period of more than five years have revealed that the cultivation of olive trees, using the system of vegetation cover, is very competitive when well managed compared to traditional methods, with or without ploughing. In certain cases, an improvement of olive tree productivity was observed compared to cultivation on bare soil.

Conclusion

It is necessary to promote the sustainable exploitation of arable lands compatible with the management of natural resources, landscape protection and the conservation of genetic diversity.

Cultivation of the olive tree with vegetation cover offers numerous advantages in this regard:

  • soil losses due to erosion are reduced.
  • soil permeability has risen, which improves water filtration in the soil.
  • evapo-transpiration of the soil has diminished.
  • certain vegetation covers help combat weeds.
  • more water is available to the olive tree during its vegetative cycle, especially in Spring.
  • the vegetation cover shelters numerous species of insects and birds that construct their nests close to the ground and thereby increase biological diversity.
  • eventually, vegetation cover as forage could benefit cattle.

There are however some negative effects:

  • wild fires may propagate more easily throughout the landscape;
  • poor management of the vegetation cover could lead to increased water consumption due to compétition that could affect productivity;
  • the vegetation cover may hinder the harvesting of olives.

This case study was proposed by Mrs Lourdes Soria Herrera.
For more information, please contact her at the following address:

Mrs Lourdes Soria Herrera
Centro Andaluz de Estudios
para el Desarollo Rural
Universidad Internacional
de Andalucía
Sede Antonio Machado
Plaza de Santa María s/n
23440 Baeza (Jaen)
Spain

Tel. (+34) 953 742775
Fax (+34) 953 742975
E-mail: lsh@uniaam.uia.es

activities

pencil

The teacher explains
the methods of olive cultivation to the class.

pencil

Where is Spain?
Is your country on the same continent as Spain?
What characterizes the climate of Spain compared to your country?

smile

Draw the Andalusian olive plantations before and after the project to combat desertification and erosion.
In your first drawing, show how the earth around the olive trees is bare and eroded. In your second drawing, draw the vegetation cover growing around the olive trees that protect the soil. Paste your picture to the wall chart
(See Teacher’s Guide).

smile

Are the desertification problems in Andalusia similar to those
of your region?
What are the differences?
What are the similarities?

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How would you arrange the vegetation cover to protect the soil in your region?
Where would it be necessary and possible to plant?
Which plants would you use?

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Tick the correct answers from
the following:

In Spain, vegetation cover
is planted between the olive
trees to:

• improve the olive harvest.
• combat parasites.
• combat land degradation.
• act as a firebreak.
• increase biological diversity.
• improve soil quality.
• combat erosion.


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