Consolidation of mechanical embankments using olive trees (Wafa SAIDI)

Biological consolidation of mechanical benches with olive trees (Tunisia)

Description

The biological consolidation of embankments is an agricultural practice that entails planting embankments with arboricultural, pastoral, or forage species. This cultivation technique enhances the effectiveness and longevity of these structures.

Anti-erosion banks are widespread in central Tunisia. In semi-arid environments, these structures consist of earthen levees built perpendicular to the slope of the land accompanied by a channel designed to retain runoff water and sediment between the banks.
Implementing and maintaining these structures can be financially burdensome for farmers, necessitating biological consolidation to ensure their long-term viability. Consolidation can be achieved using various types of tree, pasture and fodder plantations. Successful biological consolidation is contingent on factors such as soil type (nature, relief), climate (particularly annual rainfall), irrigation water resources and the species chosen. Most farmers use olive trees to consolidate soil and water conservation structures in their plots.
Consolidation efforts encompass both recent and aging structures, focusing on rehabilitation and ongoing maintenance. Planting occurs on the embankments and within their channels, providing essential plant cover and root systems that bind soil particles, reducing the risk of erosion. This technique has proven to enhance soil fertility, boost crop yields, and generate income for farmers through the sale of olives and olive oil. Despite the 10-15% loss of land surface associated with embankment installation, the consolidation process increases the overall value of the land. The presence of olive trees enhances the land's worth.

Location

Location: Sidi Bouzid, Tunisia

No. of Technology sites analysed: single site

Geo-reference of selected sites
  • 9.3342, 35.28165

Spread of the Technology: evenly spread over an area (approx. 1,000-10,000 km2)

In a permanently protected area?: No

Date of implementation: 1998

Type of introduction

Classification of the Technology

Main purpose
  • improve production
  • reduce, prevent, restore land degradation
  • conserve ecosystem
  • protect a watershed/ downstream areas – in combination with other Technologies
  • preserve/ improve biodiversity
  • reduce risk of disasters
  • adapt to climate change/ extremes and its impacts
  • mitigate climate change and its impacts
  • create beneficial economic impact
  • create beneficial social impact
Land use
Land use mixed within the same land unit: Yes - Agro-pastoralism (incl. integrated crop-livestock)

  • Cropland
    • Tree and shrub cropping: olive
    Number of growing seasons per year: 1
    Is intercropping practiced? No
    Is crop rotation practiced? No
  • Grazing land
    • Ranching
    Animal type: sheep
    Is integrated crop-livestock management practiced? No
      SpeciesCount
      sheep50
    • Settlements, infrastructure - Settlements, buildings, Energy: pipelines, power lines
    Water supply
    • rainfed
    • mixed rainfed-irrigated
    • full irrigation

    Purpose related to land degradation
    • prevent land degradation
    • reduce land degradation
    • restore/ rehabilitate severely degraded land
    • adapt to land degradation
    • not applicable
    Degradation addressed
    • soil erosion by water - Wt: loss of topsoil/ surface erosion
    • chemical soil deterioration - Cn: fertility decline and reduced organic matter content (not caused by erosion)
    • biological degradation - Bc: reduction of vegetation cover, Bh: loss of habitats
    SLM group
    • improved ground/ vegetation cover
    • integrated soil fertility management
    • cross-slope measure
    SLM measures
    • vegetative measures - V1: Tree and shrub cover
    • structural measures - S1: Terraces

    Technical drawing

    Technical specifications
    - Slope < 20%.
    - Distance between olive trees: 10 m

    Establishment and maintenance: activities, inputs and costs

    Calculation of inputs and costs
    • Costs are calculated: per Technology area (size and area unit: 1 ha)
    • Currency used for cost calculation: Tunisian dinars
    • Exchange rate (to USD): 1 USD = 3.1 Tunisian dinars
    • Average wage cost of hired labour per day: n.a
    Most important factors affecting the costs
    - Availability of workers
    Establishment activities
    1. Purchase olive seedlings (Timing/ frequency: None)
    2. Preparing holes (Timing/ frequency: None)
    3. Planting (Timing/ frequency: None)
    Total establishment costs (estimation)
    600.0
    Maintenance activities
    1. Weed clearance (Timing/ frequency: None)
    2. Prunning (Timing/ frequency: None)
    3. Irrigation (Timing/ frequency: None)
    Total maintenance costs (estimation)
    1000.0

    Natural environment

    Average annual rainfall
    • < 250 mm
    • 251-500 mm
    • 501-750 mm
    • 751-1,000 mm
    • 1,001-1,500 mm
    • 1,501-2,000 mm
    • 2,001-3,000 mm
    • 3,001-4,000 mm
    • > 4,000 mm
    Agro-climatic zone
    • humid
    • sub-humid
    • semi-arid
    • arid
    Specifications on climate
    Average annual rainfall in mm: 229.0
    - Random and irregular annual rainfall
    - Autumn and spring are the seasons with the highest levels of rainfall
    Name of the meteorological station: Sidi Bouzid (INM)
    The average temperature is 18°C.
    Slope
    • flat (0-2%)
    • gentle (3-5%)
    • moderate (6-10%)
    • rolling (11-15%)
    • hilly (16-30%)
    • steep (31-60%)
    • very steep (>60%)
    Landforms
    • plateau/plains
    • ridges
    • mountain slopes
    • hill slopes
    • footslopes
    • valley floors
    Altitude
    • 0-100 m a.s.l.
    • 101-500 m a.s.l.
    • 501-1,000 m a.s.l.
    • 1,001-1,500 m a.s.l.
    • 1,501-2,000 m a.s.l.
    • 2,001-2,500 m a.s.l.
    • 2,501-3,000 m a.s.l.
    • 3,001-4,000 m a.s.l.
    • > 4,000 m a.s.l.
    Technology is applied in
    • convex situations
    • concave situations
    • not relevant
    Soil depth
    • very shallow (0-20 cm)
    • shallow (21-50 cm)
    • moderately deep (51-80 cm)
    • deep (81-120 cm)
    • very deep (> 120 cm)
    Soil texture (topsoil)
    • coarse/ light (sandy)
    • medium (loamy, silty)
    • fine/ heavy (clay)
    Soil texture (> 20 cm below surface)
    • coarse/ light (sandy)
    • medium (loamy, silty)
    • fine/ heavy (clay)
    Topsoil organic matter content
    • high (>3%)
    • medium (1-3%)
    • low (<1%)
    Groundwater table
    • on surface
    • < 5 m
    • 5-50 m
    • > 50 m
    Availability of surface water
    • excess
    • good
    • medium
    • poor/ none
    Water quality (untreated)
    • good drinking water
    • poor drinking water (treatment required)
    • for agricultural use only (irrigation)
    • unusable
    Water quality refers to: both ground and surface water
    Is salinity a problem?
    • Yes
    • No

    Occurrence of flooding
    • Yes
    • No
    Species diversity
    • high
    • medium
    • low
    Habitat diversity
    • high
    • medium
    • low

    Characteristics of land users applying the Technology

    Market orientation
    • subsistence (self-supply)
    • mixed (subsistence/ commercial)
    • commercial/ market
    Off-farm income
    • less than 10% of all income
    • 10-50% of all income
    • > 50% of all income
    Relative level of wealth
    • very poor
    • poor
    • average
    • rich
    • very rich
    Level of mechanization
    • manual work
    • animal traction
    • mechanized/ motorized
    Sedentary or nomadic
    • Sedentary
    • Semi-nomadic
    • Nomadic
    Individuals or groups
    • individual/ household
    • groups/ community
    • cooperative
    • employee (company, government)
    Gender
    • women
    • men
    Age
    • children
    • youth
    • middle-aged
    • elderly
    Area used per household
    • < 0.5 ha
    • 0.5-1 ha
    • 1-2 ha
    • 2-5 ha
    • 5-15 ha
    • 15-50 ha
    • 50-100 ha
    • 100-500 ha
    • 500-1,000 ha
    • 1,000-10,000 ha
    • > 10,000 ha
    Scale
    • small-scale
    • medium-scale
    • large-scale
    Land ownership
    • state
    • company
    • communal/ village
    • group
    • individual, not titled
    • individual, titled
    Land use rights
    • open access (unorganized)
    • communal (organized)
    • leased
    • individual
    Water use rights
    • open access (unorganized)
    • communal (organized)
    • leased
    • individual
    Access to services and infrastructure
    health

    poor
    x
    good
    education

    poor
    x
    good
    technical assistance

    poor
    x
    good
    employment (e.g. off-farm)

    poor
    x
    good
    markets

    poor
    x
    good
    energy

    poor
    x
    good
    roads and transport

    poor
    x
    good
    drinking water and sanitation

    poor
    x
    good
    financial services

    poor
    x
    good

    Impacts

    Socio-economic impacts
    Crop production
    decreased
    x
    increased


    The land was unproductive before the embankments were created.

    crop quality
    decreased
    x
    increased

    risk of production failure
    increased
    x
    decreased


    Embankments optimize growth conditions, reducing the risk of production failure.

    farm income
    decreased
    x
    increased

    Quantity before SLM: 0%
    Quantity after SLM: 100%

    Socio-cultural impacts
    food security/ self-sufficiency
    reduced
    x
    improved

    Ecological impacts
    soil moisture
    decreased
    x
    increased

    soil cover
    reduced
    x
    improved

    soil loss
    increased
    x
    decreased

    flood impacts
    increased
    x
    decreased


    Embankments serve as barriers, slowing down water flow and reducing the risk of soil erosion through runoff. On the other hand, the olive tree's extensive root system can penetrate deep into the soil, preventing soil erosion and improving long-term stability.

    emission of carbon and greenhouse gases
    increased
    x
    decreased


    Olive trees, like other perennial woody plants, have the capacity to sequester carbon dioxide from the atmosphere. This can help mitigate climate change by reducing greenhouse gas emissions.

    Off-site impacts
    downstream siltation
    increased
    x
    decreased

    Cost-benefit analysis

    Benefits compared with establishment costs
    Short-term returns
    very negative
    x
    very positive

    Long-term returns
    very negative
    x
    very positive

    Benefits compared with maintenance costs
    Short-term returns
    very negative
    x
    very positive

    Long-term returns
    very negative
    x
    very positive

    Climate change

    Gradual climate change
    seasonal rainfall decrease

    not well at all
    x
    very well
    Season: wet/ rainy season

    Adoption and adaptation

    Percentage of land users in the area who have adopted the Technology
    • single cases/ experimental
    • 1-10%
    • 11-50%
    • > 50%
    Of all those who have adopted the Technology, how many have done so without receiving material incentives?
    • 0-10%
    • 11-50%
    • 51-90%
    • 91-100%
    Has the Technology been modified recently to adapt to changing conditions?
    • Yes
    • No
    To which changing conditions?
    • climatic change/ extremes
    • changing markets
    • labour availability (e.g. due to migration)

    Conclusions and lessons learnt

    Strengths: land user's view
    • Profitability: Planting olive trees is a profitable activity for land users and involves relatively low expense.
    • Preservation of cultural heritage: Planting olive trees is of cultural importance in Tunisia. Embracing this method of cultivation allows land users to safeguard cultural heritage and uphold traditional agricultural practices.
    • Sustainability: ensures the longevity of the embankments
    Strengths: compiler’s or other key resource person’s view
    • Olive trees are carbon sinks that help offset greenhouse gas emissions.
    • Reinforce and extend the service life of embankments.
    • Olive trees provide opportunities to develop value-added products such as olive oil, table olives and olive-based cosmetics.
    Weaknesses/ disadvantages/ risks: land user's viewhow to overcome
    • Olive trees are suited to specific climatic conditions and can be sensitive to various environmental hazards, such as extreme temperatures, drought, frost or pests and diseases. Land users must select appropriate olive varieties that are well suited to their local climatic conditions.
    Weaknesses/ disadvantages/ risks: compiler’s or other key resource person’s viewhow to overcome
    • Successful implementation of the technology hinges on suitable environmental conditions, including appropriate soil types, climatic factors and access to water resources. Feasibility studies to determine the suitability of the land for olive tree planting

    References

    Compiler
    • Wafa Saidi
    Editors
    • Siagbé Golli
    • Faouzi Harrouchi
    • faouzi BATTI
    • Fatma Maaloul
    • Tabitha Nekesa
    • Ahmadou Gaye
    Reviewer
    • William Critchley
    • Rima Mekdaschi Studer
    Date of documentation: March 6, 2023
    Last update: May 1, 2024
    Resource persons
    Full description in the WOCAT database
    Linked SLM data
    Documentation was faciliated by
    Institution Project
    Key references
    • Guide de conservation des eaux et du Sol, Ministère de l’agriculture, Direction Générale de l'Aménagement et de la Conservations des Terres Agricoles, 1995: Ministère de l’agriculture, Direction Générale de l'Aménagement et de la Conservations des Terres Agricoles: Ministry of Agriculture, Directorate-General for the Development and Conservation of Agricultural Lands
    • Carte agricole de la Tunisie, Ministère de l’agriculture, 2005: Ministry of Agriculture, Directorate-General for the Development and Conservation of Agricultural Lands
    • Analyse du système des banquettes mécaniques Propositions d'améliorations, de valorisation et d'évolution pour les gouvernorats de Kairouan, Siliana et Zaghouan, Tunisie, Eric Roose, 2002: Ministry of Agriculture, Directorate-General for the Development and Conservation of Agricultural Lands
    Links to relevant information which is available online
    This work is licensed under Creative Commons Attribution-NonCommercial-ShareaAlike 4.0 International