How contour bunding and other technologies can reduce soil erosion and raise productivity in African watersheds
Communities inhabiting Africa’s drylands frequently suffer from torrential floods and recurrent droughts. Under climate change, the situation is worsening; for example, many of the worst natural disasters recorded in East Africa have taken place in the past decade or two. Various land- and water-management practices introduced in recent years have sought to enhance farmers’ resilience to environmental shocks, before climate changes progress further.
Scientists at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), in collaboration with partner organizations, investigated the effects of such interventions. Our findings, outlined in two new publications, show that practices such as contour bunding, infiltration trenches, enclosure-based management and water-spreading weirs can help to reduce the effects of drought, limit soil loss, restore ecosystem services and enhance agricultural production.
The first paper focused on the use of contour bunding at study sites in two semiarid districts of southern Mali. Contour bunding involves laying points of equal elevation along the contour of a sloping field and then constructing a bund, or barrier, along the contour. It is aimed at reducing run-off and increasing water filtration to reduce soil erosion and nutrient loss. If trees are used to strengthen the bund, then it can also provide animal fodder and reduce the need for free grazing, particularly during the dry season.
The two sites comprised four villages in Bougouni district and five villages in Koutiala district. These districts lie within Sikasso, a region of Sudanean savanna with agriculture characterized by rainfed, small-scale crop, livestock and integrated agro-pastoral farming systems. The sites had differing agro-ecologies, with Bougouni receiving 1,060 mm mean annual rainfall, and Koutiala 862 mm. In response to these climatic conditions, Bougouni farmers tend to grow maize and sorghum, while those living in Koutiala cultivate millet and other dryland crops. Cotton is an important cash crop in both areas.
Our research team began by establishing technology parks within each study site to conduct agronomic and environmental monitoring, and demonstrate the benefits of contour bunding to farmers. At each technology park, we constructed contour bunding in some areas and left other areas free of intervention, before sowing locally grown crops. We installed equipment to measure run-off, soil erosion and soil moisture in both bunded and non-bunded fields.
From the start of the project in 2014, our researchers were able to demonstrate to farmers and regional agricultural bureau experts that the level of run-off collected after heavy rains from the bunded fields was lower than from the non-bunded ones. We worked with a local NGO, which provided a contour line-marking service to farmers for only USD 10 per farm. As farmers started to see the benefits of the contour bunding, they began paying to implement the technology in their own fields. In total, more than 2,500 farmers applied the technology across the two study sites.
Over the course of the six-year project, which was supported by the CGIAR Research Program on Water, Land and Ecosystems (WLE) and USAID Feed the Future Africa RISING project, we continued to collect data on run-off, water filtration and soil erosion (including volumes of sediment and nutrients, such as nitrogen and phosphorus) at the demonstration sites as well as in 45 bunded and non-bunded farmers’ fields. We also collected agronomic data, including the dates of crop sowing and weeding, number of plants emerging after two weeks, amount of fertilizer applied and crop yield. Finally, we gathered socio-economic data, such as the breakdown of farming responsibilities across male, female and youth members of households; farm productivity; and income levels.
Our findings showed that constructing contour bunding helped to retain soil and nutrients, reduce land degradation and increase crop productivity. Significantly, implementing contour bunding reduced soil loss by 163%, and the majority of farmers (78%) perceived that they earned a higher income from crops sown in bunded fields.
While the technology was acceptable to local farmers, it was largely men in the households who made decisions to install the bunding and cultivate crops. Empowering women to also grow crops in bunded fields could help to further enhance productivity and food security in the region. The technology was rolled out to a further 3,700 farmers as a result of initiatives run by Care International and DFID, and there is scope for further scaling up.
Highlighting best practices
The paper in which the findings were outlined formed part of a wider review of soil conservation best practices published as a special issue of the journal Renewable Agriculture and Food Systems. In this special issue, an additional seven papers showed promising findings, such as that: implementing soil and water conservation interventions can reduce runoff and soil erosion at plot and landscape scales; the use of infiltration trenches and reseedingwith the grass Chloris gayana can increase forage yields; and water-spreading weirs can effectively capture floodwaters and sediment from highlands locations, spurring the creation of new farming systems.
A spiral of land degradation and water scarcity in dryland areas has commonly reduced access to animal feed and human food, increased conflicts, reduced farm incomes and reduced once-secure communities to poverty and food insecurity. Sadly, there are now many examples across the Sahel where land degradation, poverty, food insecurity and conflicts intersect with climate change, driving increased variability of rainfall and extreme events. However, as the projects showcased in this article demonstrate, implementing simple and low-cost technologies can be beneficial in dryland areas, by raising agricultural productivity and helping to underpin food security.
This post was first published on the Thrive blog and written by Birhanu Zemadim (ICRISAT), Anthony Whitbread (ICRISAT), and Carolyn Fry (WLE).