2 Status of soil health and water management in Africa

2.1 Major threats to soil health in Africa

Threats to soil health are processes or direct drivers that cause soil quality deterioration over time. They can be generally categorized as soil degradation, the negative impacts of climate change, and misuse/abuse of the soil resource (Table 2.1). The first seminal work on the global extent of threats to soil health was undertaken in the late 1980s (Oldeman 1992). New global estimates have since been published in terms of rates of soil erosion, salinization, pollution, nutrient depletion, etc., which show an increasing trend of the extent and intensities of some of the threats to soil health (FAO 2021; Hassani, Azapagic, and Shokri 2021; Tan, Lal, and Wiebe 2005; Wuepper, Borrelli, and Finger 2020). There are also reports of regional prioritization of the main threats, which depict soil degradation as the most dominant global threat to soil health (Montanarella et al. 2016).

Table 2.1: Major threats to soil health
Major.Group Threat Reference
Soil degradation Physical degradation (e.g., erosion, compaction, sealing, structural deterioration, etc.) (Saljnikov et al. 2022)
Chemical degradation (e.g., salinization, acidification, sodification, nutrient imbalance, organic carbon loss, nutrient depletion, etc.) (Oldeman 1992)
Biological degradation (loss of soil biodiversity) (Sims 1990)
Climate change Drought (e.g., desiccation, soil moisture decline), flooding (waterlogging) (Girija Veni et al. 2020)
Misuse or abuse of soil resource Soil nutrient mining/depletion (Tan, Lal, and Wiebe 2005)
Soil pollution and contamination (e.g., waste disposal, wastewater, deposition of heavy metals, oil spills, microplastics, etc.) (FAO 2021)
Loss of soil vegetative cover, soil mixing (e.g., mining, urbanization, excavations and constructions, microplastics, etc.) (Ihenetu et al. 2024)

In Africa, soil degradation remains the major threat to soil health (Figure 2.1) (Jones et al. 2013; Montanarella et al. 2016). The extent and intensity of soil degradation on the continent has been variously estimated in literature. Oldeman (1992) estimated it at 65% of agricultural land, 31% of permanent pasture, and 19% of forested land in Africa. Recent estimates have been more specific to the types of degradation and have estimates that vary depending on the methods used. For example, Wuepper, Borrelli, and Finger (2020) estimated that 80% of Africa is affected by slight erosion and more than 12% is affected by moderate and high soil erosion rates. The Soil Atlas of Africa reported more than 26% of Africa as vulnerable to desertification (Jones et al. 2013) while Omuto et al. (2024) reported 10% of land area and 0.2% of croplands in Africa as affected by salinization. More work is needed to give an accurate estimation of the extent and intensity of the major soil health threats in Africa.

Example of approximate distribution of some types of soil degradation in Africa (adapted from Jones et al. 2013)

Figure 2.1: Example of approximate distribution of some types of soil degradation in Africa (adapted from Jones et al. 2013)

2.2 Responses to soil threats in Africa

2.2.1 Soil and water conservation

Soil and water management practices respond to soil threats by implementing strategies for controlling soil degradation and mitigating climate change effects. The practices are grouped as agronomic, vegetative, structural, and management measures (Table 2.2). The literature includes many soil and water conservation practices for different agro-ecological zones (Blanco and Lal 2010; FAO 1966). Some of the practices have been documented in the WOCAT database (https://explorer.wocat.net/, accessed on 20 June 2024).

Table 2.2: Soil and water conservation practices
Main.group Features Practices
Agronomic Use of cropping and tillage methods to increase soil moisture and nutrients, dissipate raindrop impact and increase the resilience of cropland Cropping methods (e.g., strip, contour, mixed, relay cropping, etc.), crop selection, mulching, crop rotation, soil fertilization, tillage, etc.
Vegetative Use of vegetation to improve soil cover, dissipate erosive power of wind or water (e.g., raindrop impact, to limit abrasive power of wind and runoff speed), as nitrogen-fixing fodder, etc. Grass strips, hedgerows, windbreaks, agro-forestation, woodlots, etc.
Structural Engineering methods to modify land slope, direct runoff, reduce runoff speed, trap runoff/rainwater, etc. Terraces, ditches, pits, ridges, drains, rainwater harvesting, bunding, etc.
Management Management of land use, salinity, pests and diseases, management of soil moisture, etc. Wetland restoration, area closure, rotational grazing, soil amendment, irrigation, pest and disease control, etc.

The adoption of soil and water conservation practices varies from place to place due to many factors, including agro-ecological zones, climate, soil types, topography, target threats to soil health, socio-economic factors, and land tenure, etc. (Asafu-Adjaye 2008; Belayneh 2023; Rotich et al. 2024; Savari, Yazdanpanah, and Rouzaneh 2022; Wordofa, Okoyo, and Erkalo 2020). Diop et al. (2022), Negassi et al. (2002), Namirembe, Nzyoka, and Gathenya (2015), and Reij (1991) have documented some of the practices in different parts of Africa. Proper documentation and spatial distribution, including at the local and national levels, are needed for promoting and scaling successful practices in different parts of Africa. Example distribution as shown in Figure 2.2 needs to be developed, periodically updated, and its information system enriched and shared with extension officers and farmers at all levels in the continent.

Factors influencing effectiveness of soil and water conservation in promoting soil health are:

  1. Proper design and appropriate use of the practices
  2. Use of catchment or landscape approach in implementing appropriate practices
  3. Adequate and regular maintenance of selected practices
  4. Combined application of different practices
  5. Adequate research and periodic improvements of the best practices in given scenarios
  6. Suitable scaling and promotion of successful practices
  7. Proper capacity building and awareness campaigns
  8. Adequate information systems to support management, promotion, and scaling of the practices
Examples of soil and water management practices in Africa (adapted from WOCAT database)

Figure 2.2: Examples of soil and water management practices in Africa (adapted from WOCAT database)

2.2.2 Policy and legislative interventions

Policy and legislative support in soil protection is an area of globally recognized crucial response for halting or controlling the advancement of threats to soil health. Policies and legislation provide the instruments needed to raise necessary resources (including budgetary allocations) to fund activities/measures against soil threats, the basis for legal restrictions to human actions promoting the advancement of threats to soil health, and the framework for coordinating actions for soil protection, among others (Montanarella 2015). Since the European Soil Charter of 1972 and the first World Soil Charter in 1981, and its revision in 2015, there has been a growing global debate about the need for a formal binding framework for soil protection (Ruppel 2022). Many countries have, therefore, developed various environmental and soil protection laws and guidelines. The Food and Agriculture Organization of the United Nations (FAO) developed a global online database (FAOLEX) detailing national laws, regulations and policies on food, agriculture and natural resources management in different countries (https://www.fao.org/faolex/en/, accessed on 20 June 2024). FAO also developed another database for soil-related national laws, regulations, and policies in all countries (https://www.fao.org/soils-portal/soilex/soil-keywords/waterlogging/en/, accessed on 20 June 2024). Although these databases are not complete, they give an indication of available soil protection policies and legislation in individual countries. An analysis of the database of African documents gives the impression that there are insufficient policies and legislation in the continent to support actions against soil chemical degradation and misuse or abuse of the soil resource (Figure 2.3a).

Summary of legal instruments for soil protection in Africa in FAO SoiLEX database

Figure 2.3: Summary of legal instruments for soil protection in Africa in FAO SoiLEX database

The FAO SoilLEX database portrays most countries in Africa as lacking adequate soil protection policies and legislation. For example, it shows that although the total number of soil conservation legal instruments may be significant, they are mostly found in less than half of the countries on the continent. Furthermore, it shows that more than 20% of countries in Africa do not seem to have clear soil protection policies and legislation (Figure 2.3b). Therefore, more work is needed to update the database, sensitize and rally African countries to improve formulation and enactment of relevant national policies and legislation for soil protection, and to raise awareness and mobilize the countries to enforce the national soil protection policies and legislation.

2.2.3 Research on soil and water management

Research is crucial in generating information and advancing knowledge on different soil and water management measures and their impacts on the threats to soil health. In this regard, research is mainly responsible for:

  1. Generating and sharing information and data regarding soil water management and soil health
  2. Developing soil health trends with/without appropriate soil and water conservation measures
  3. Comparing successes and causes for failure of existing soil and water conservation measures
  4. Evaluating impacts of different conservation measures and their scaling requirements
  5. Developing new methods, technologies, and equipment for soil and water conservation
  6. Guiding decisions and identifying critical areas for targeting soil conservation measures

The trend in research on soil and soil water at the global scale is shown in the literature as having had an exponential growth between 1934 and 2022, which indicated an increasing research interest in soil water management over the years (Dumanski 2009; Jia et al. 2024; Zhang et al. 2020). However, the trend does not portray a prominent presence of African research on soil water and soil conservation. Africa has many agriculture research centers (African Agricultural Research (1996)), at least four sub-regional agricultural research organizations (https://faraafrica.org/partnerships/, accessed on 3 July 2024), and many soil scientists, soil science societies and international soil research centers (Rozanov and Wiese 2018; Ryan et al. 2002). Yet, the research activities regarding soil and water conservation from Africa do not significantly reflect in these global research trends. This shows that more work is still needed to improve research on soil and water conservation in Africa, which is commensurate with global trends. Nonetheless, research in Africa on soil water management has demonstrated different approaches to and types of conservation practices, adoption of soil management technologies, impacts of management measures, challenges with ongoing conservation measures, etc. (Critchley and Graham 1991; Diop et al. 2022; Reij 1991; Wolka, Mulder, and Biazin 2018).

2.2.4 Extension and advisory services on soil and water management

Extension and advisory services provide the link between research or technology/policy development with the end users (such as farmers or owners of land). They are important in:

  • Information and technology transfer
  • Feedback for improvements
  • Awareness campaigns
  • Product promotion
  • Adoption of technology
  • Catalyzing scaling strategies
  • Capacity-building

Extension service is the engine for driving the implementation of soil and water conservation measures. During the 20th century, agricultural extension was dominated by government researchers and extension workers (Greenwood 1986; Rivera and Qamar 2003; Swanson et al. 1997). In Africa, the implementation design for extension services changed at the end of most donor-supported extension programs, which also saw the entry of the private sector and non-governmental organizations (NGOs) (Nwafor, Ogundeji, and Nwafor 2021; Saliu, Obinne, and Audu 2009). The trend of extension and advisory services has since changed in the continent and new methods through digital platforms are being considered in various agricultural sub-sectors (FAO 2023). Although the use of digital extension and advisory services has not prominently taken root in the soil and water conservation sub-sector, there are many promising opportunities which can be further developed. This is the current rallying call by most leading organizations involved in extension and advisory services in Africa (e.g., https://www.afaas-africa.org/). These organizations are embracing digital technology and slowly advocating for e-extension and e-advisory approaches to improve soil health in Africa.

2.2.5 Awareness campaigns and mobilization to improve soil and water conservation

Awareness campaigns and community mobilization are popular techniques for capturing public attention, improving community knowledge, empowering communities, influencing decisions, and rallying the public and local communities to work together towards improving soil and water conservation (Mango et al. 2017). While awareness campaigns target at raising public consciousness and change of behavior towards promoting soil and water conservation practices, mobilization is concerned with increasing public participation and involvement in conservation efforts. Many countries have used awareness campaigns and community mobilization to expand the coverage and overall effectiveness of soil and water conservation efforts. Figure 2.4 shows some of the strategies often adopted by countries in Africa to raise awareness and mobilize communities to promote soil and water conservation measures (Khan 1997; Mango et al. 2017; Wood 1997).

Awareness and mobilization strategies for soil and water conservation

Figure 2.4: Awareness and mobilization strategies for soil and water conservation

Impacts of awareness campaigns and community mobilization towards soil and water conservation have been reported as being able to (Dangiso and Wolka 2023; Masha et al. 2021; Willy and Holm-Müller 2013):

  1. Improve public perception and attention to practices that promote soil health
  2. Facilitate scaling strategies for soil and water conservation measures,
  3. Catalyze landscape-level activities which limit threats to soil health,
  4. Improve the adoption rate of soil and water conservation measures
  5. Encourage innovations and investments in soil and water conservation

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