Background 1 2
High intensity rainfall is characteristic of large areas of the Sahel causing widespread rainfall runoff and erosion. Priority has therefore been given to a range of measures for run-off and soil erosion control. One such measure, the use of stone bunds built on natural contour lines, has been promoted and supported by governments, NGOs, extension agents and farmers for more than 25 years and is now widely used in the Sahel. The best results are often achieved when contour stone bunds are used in combination with the planting of grass and trees on the contour lines. In addition, where soils are particularly susceptible to surface crusting and runoff, farmers often combine contour stone bunds with ‘zai’ planting pits, which are 10-20 cm deep and act as micro-catchments into which crops are planted (Roose et al. 1999). 3
Relationship to CSA
Contour stone bunds are beneficial under both wetter and drier climate change scenarios. In wetter years they help to reduce the climate-induced risk of run-off and erosion. In drier years, they contribute to effective rainwater harvesting. In addition, since heavy rainfall events in the Sahel are projected to increase with global warming, durable and effective soil erosion control structures will assume even greater importance and constitute an important adaptation measure. In addition, when tree lines and/or grass strips are also planted on the contour, they have the potential to contribute to above and below ground soil carbon sequestration.
Impacts and lessons learned
Region-wide, it is estimated that about 300,000 ha of land has been reclaimed. However, contour stone bunds are labour intensive and costly. For example, between 1987 and 2006 in Burkina Faso, the PATECORE project supported the reclamation of over 100,000 ha of degraded land with 30,000 km of CBS. However, this required the quarrying and transport of 2.5 million cubic meters of stones at a net cost of US$ 200/ha and between 100-150 person days of unpaid farmer labor per hectare. Nevertheless, they have proven to be both highly effective and durable and often act as a catalyst for additional innovations such as tree or grass planting on the bunds, as well as increased levels of nutrient inputs on field crops.
References
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1
Landolt M. 2011. Stone lines against desertification. Rural 21, January 2011.
http://www.rural21.com/fileadmin/_migrated/content_uploads/Stone_lines_against_desertification_01.pdf This brief provides farmer information and success stories on the practice of using stole contour lines to improve rainwater use and slow erosion in Burkina Faso. -
2
Barry B, Olaleye AO, Zougmore R, Fatondji D. 2008. Rainwater harvesting technologies in the Sahelian zone of West Africa and the potential for outscaling. IWMI Working Paper 126. Colombo, Sri Lanka: International Water Management Institute.
http://www.iwmi.cgiar.org/Publications/Working_Papers/working/WOR126.pdf In West Africa, especially in the Sahelian countries of Burkina Faso, Niger, Mali, and Mauritania, erratic rainfall sequences within and between years has often led to a high uncertainty in rainfed crop production. Over the past three decades, severe food shortages attributed to drought have been frequently reported in several Sahelian countries, most of which are amongst the least developed of the world. The long dry periods affecting the majority of the arid and semi-arid countries in West Africa are associated with famine, displacement of populations, and loss of previously fertile land. One of the challenges of the Millennium Development Goals (MDGs) is to reduce poverty and hunger and ensure successful interventions are reported in rainfed agriculture in West Africa, which are transforming the livelihoods of many resource poor smallholder farmers. Innovative and indigenous ways to achieve improved crop yields through integrated land and water management such as rainwater harvesting and soil water conservation have been successfully tested and, in some cases, adopted in West Africa. This paper highlights the successful interventions of improved indigenous rainwater harvesting/soil water conservation technologies such as Zaï or tassa, stone rows and halfmoon in the Sahelian zones of West Africa over the past 10 years, and their contributions to enhancing food security and alleviating poverty. The potential for adoption of these technologies at the farm level and their outscaling to areas with similar agroecological zones are also discussed. -
3
Roose E, Kabore V, Guenat C. 1999. Zai Practice: A West African Traditional Rehabilitation System for Semiarid Degraded Lands, a Case Study in Burkina Faso. Arid Soil Research and Rehabilitation 13(4):343-355.
http://dx.doi.org/10.1080/089030699263230 For degraded soil productivity, restoration, and green cover rehabilitation, it is essential to study and improve traditional farming systems, especially in the Sudano - Sahelian areas, where technical possibilities are limited. One example is the Zai practice, a very complex soil restoration system using organic matter localization, termites to bore channels in the crusted soils, runoff capture in microwatersheds, and seed hole cropping of sorghum or millet on sandy soils. Investigation on many fields of the Mossi Plateau (northern part of Burkina Faso) has shown a range of variations of the Zai system in relation to soil texture, availability of labor and organic matter, and relevance for rehabilitation of these degraded crusted soils. We describe a complex soil restoration system revealed during our 2 years of inquiries and experiments testing this system in two types of soil (a shallow, poor alfisol and a deep, brown tropical inceptisol). Biomass production of sorghum is reported in relation to various potential improvements of the Zai systems and also the wild grass and shrub species that appeared after 2-7 years of a Zai cropping system on a bare, crusted, degraded soil surface. Experimental improvements of this Za system on two soils confirm the possibility not only to increase the production of cereal grains (from 150 to 1700 kg ha-1) and straw (from 500 to 5300 kg ha-1) on deep, brown soils (eutropept), but also to reintroduce a large diversity of useful plants that may help during the fallow period and the process of degraded soil restoration. The concentration of runoff water, organic manure, and a complement of mineral nutrients in microwatersheds increased biomass production without significant change in soil properties after 2 years. This system may be useful not only to restore soil productivity but also for revegetation, e.g., 22 species of weeds and 13 species of forage shrubs included in dry dung manure (3 Mg ha-1 yr-1).