What does SLM achieve?
Increasing agricultural land productivity for food, fodder, fiber and fuel remains a priority in Sub-Saharan Africa. This can be achieved by: intensification and diversification of agricultural production and expansion of the agricultural area.
Four principles help increase land productivity:
- Increasing water productivity
- Enhancing soil fertility
- Improving plant management
Creating favorable micro
Increasing land productivity, Ethiopia. (William Critchley)
Water management is an entry point into SLM. Good SLM means good water management. Water productivity is the yield produced per unit of water, and sometimes also measured as value produced per unit of water. Minimizing water losses increases water productivity.
The figure to the right illustrates three major sources of water loss in agriculture: evaporation from the soil surface, surface runoff, and drainage.
Water management can be divided into management of (a) rainfed agriculture and (b) irrigated agriculture. Since 93% of farmland in Sub-Saharan Africa is rainfed, and a large proportion is dryland (where water is the main limiting factor to food production), rainwater management is crucial in the region.
Productive water (transpiration) and water losses (evaporation and runoff) without water conserving measures in dry lands.
Where there is excess water in humid environments, or at the height of the wet seasons in subhumid conditions, the soil and ground water can become saturated, or the soil’s infiltration capacity can be exceeded. Thus safe discharge of surplus water is necessary. This helps avoid leaching of nutrients, soil erosion, or landslides. It can be achieved through the use of graded terraces, cut-off drains and diversion ditches, etc.
Strategies in rainfed agriculture water management, dependent on the zone, are to:
Uncontrolled runoff causes erosion – and represents a net loss of moisture to plants where rainfall limits. The strategy here is to slow runoff, allowing more time for the water to infiltrate into the soil and reducing the damaging impact of runoff through soil erosion. It is applicable to all climates. This can be accomplished through the use of vegetative strips, earth and stone bunds, terraces, etc.
In situations where rainfall limits plant growth, the strategy is to avoid any movement of water on the land in order to encourage rainfall infiltration. Thus water storage is improved within the rooting depth of plants, and groundwater tables are recharged. This is crucial in subhumid to semi-arid areas. The technologies involved are cross-slope barriers, mulching, vegetative cover, minimum/no tillage, etc.
Harvesting runoff water is appropriate where rainfall is insufficient and runoff needs to be concentrated to improve plant performance. Planting pits, half moons, etc. can be used. This can also be applied in environments with excess water during wet seasons, followed by water shortage: dams and ponds can further be used for irrigation, flood control or even hydropower generation.
Water loss from the soil surface can be reduced through soil cover by mulch and vegetation, windbreaks, shade, etc. This is mainly appropriate in drier conditions where evaporation losses can be more than half of the rainfall.
Strategies in irrigation water management are to:
Water Losses1. Evaporation from water surface2. Deep percolation in water canals3. Seepage through canal bunds / walls4. Overtopping5. Surface runoff / drainage6. Deep percolation belo root zone7. Evaporation loss8. Productive transpiration by plants(Studer, 2009)
- Reduce Canal losses
- Manage scheduling and institutions
- Manage Storage
- Improve irrigation technology
- Use deficit irrigation and supplementary irrigation
Africa’s soils are heavily depleted of nutrients, and soil organic matter may be as little as 0.5% in the topsoil (Bot/Benites, 2005). Still, ‘nutrient mining’ continues, with a net annual loss of 8 million tons of NPK (Verchot et al 2007, WB 2010). This results from soil erosion, removal of crop products and residues, leaching of nutrients below root depth, volatisation, and accelerated mineralization of SOM through tillage.
The nutrient and carbon cycle showing the main losses and gains / replenishments of soil organic matter, biomass and nutrients.
Fertile soil is the foundation for land productivity. Soil organic matter, nutrient content and soil structure are the main factors influencing fertility. Of the three, soil organic matter (SOM) is the most important as it absorbs and holds nutrients, and is fundamental for good soil structure.
SLM practices can improve SOM and the nutrient cycle: these include soil cover through residues and plants, crop rotation, intercropping, agroforestry, fallowing, input from compost and animal manure, and incorporation of green manure. These can be supplemented by inorganic fertilizer and minimum disturbance of soil during tillage.
Improved water management further enhances these practices.
Improved agronomy through microdosing.
Composting, manuring and mulching in a banana plantation, Uganda. (William Critchley)
Crop rotation, Zambia. (Martin Sishekanu)
Conservation agriculture with agroforestry, Zambia. (Mei Xie)
Ground cover with residues. (Mei Xie)
Ground cover with residues. (Mei Xie)
Plant management focuses on selection of crop varieties – important traits are high/ reliable yield, drought adaptation and pest/disease resistance. Management of weeds, pest and diseases has an impact on production. Integrated Pest Management is important, as is weed control through crop rotation, mulching and living ground cover. Plant management includes dealing with invasive species in forestry and control of undesirable species in rangelands.
Invasive alien plants in grazing land. (William Critchley)
Screening for drought tolerance of pigeon peas and lablab. (Hanspeter Liniger)
The development of improved microclimates helps create favorable temperature and humidity for production.
Agroforestry techniques are the clearest example: shelterbelts and windbreaks, and other agroforestry systems that reduce wind and improve shade, and simultaneously build up nutrients in the soil.
A windbreak with two or three tree lines planted 5 m apart established between fields of annual crops. (Idrissou Bouraima)
Microclimates offer shade for livestock. (William Critchley)
Costs and benefits help indicate how SLM adoption can impact livelihoods. Investments in SLM should aim at long-term, sustained paybacks. But short-term, rapid benefits are highly appreciated by farmers.
High labour costs for ridging and low returns (left) compared to less demanding mulching with high benefits (right). (Hanspeter Liniger)
The following table gives some examples of SLM practices that have different payback periods.
Below are four principles for improving livelihoods:
- Providing short and long term benefits
- Assisting small scale subsistence land users with establishment costs
- Assisting establishment if short-term benefits are not guaranteed.
- Letting maintenance costs be covered by land users
Prevention, mitigation and rehabilitation of land degradation less than half a kilometer apart. (Hanspeter Liniger)SLM can prevent or mitigate land degradation. It can also rehabilitate degraded land. These graphs show different categories of SLM measures. Priority should be given to agronomic and vegetative measures, before considering costly structural measures. It is good to consider a combination of measures to suit local conditions.
Without healthy biodiversity, production systems will not be sustainable. Thus, the best SLM practices are those that conserve biodiversity and thereby enhance ecosystem function. Sub-Saharan Africa hosts some of the most bio-diverse regions in the world – but those which are tourist attractions and income generating are endangered. SLM that protects biodiversity sustains woodlands, grasslands, wetlands, parklands, as well as agricultural lands – and associated livelihoods.
Giraffes in the Amboseli National park, Kenya. (Hanspeter Liniger)
Africa is especially vulnerable to climate change because of its marginal rainfall and temperature regimes, and reliance on agriculture which is a climate-sensitive sector. It is also vulnerable because of the low incomes per capita.
SLM offers land users opportunities to address climate change impacts through adaptation, and increase their resilience to climate change. By increasing soil organic matter, land users not only enhance their land fertility and production, but also improve soil water storage capacity. This helps when drought comes. At the same time, enriching soils with organic matter sequesters carbon from the atmosphere. SLM can also lower GHG emissions through improved livestock management, reduced land degradation, minimised machinery use, and management of forest and pasture lands. These help reduce climate change impacts.
Synergies between adaptation and mitigation – SLM practices generating multiple benefits.Now that you have learned about what SLM acheives, proceed to learn the 8 SLM practices by clicking on "Next".
SLM practices must be environmentally friendly. They should reduce land degradation, enhance biodiversity, and build climate change resilience.
Chagga homegardens with the snow-capped peak of Mt. Kilimanjaro in the background. (Hanspeter Liniger)
Biodiversity in drylands. – a sign of environmental protection and sustainability. (William Critchley)