58, Winter 2005
Soil management for drylands
The year 2006, declared the International Year of Deserts and Desertification (IYDD) by the United Nations (1), has the following two goals:
Soil management, the theme of Arid Lands Newsletter No. 58, was chosen to support both of these aims.
First, understanding the physical nature of dryland soils is basic to understanding drylands ecosystems, since soil is integral both to the sustenance of life and to basic global processes such as carbon and nitrogen cycling. Second, soil degradation lies at the heart of desertification, which is essentially the result of unsustainable land use. Typically, two main drivers of desertification are increasing population pressures and poverty; another potential driver is climate change. These interact in complex ways that can lead to unsustainable livelihood practices like overgrazing, excessive cropping, or deforestation. The end result can be vegetation loss, leading in turn to problems like soil erosion, compaction, or nutrient loss. Ultimately this loss of soil function and fertility can lead to a vicious cycle of further desertification and loss of both livelihoods and biodiversity.
The distinction between deserts and desertification, emphasized in the goals of the IYDD, is crucial. As the "Conference Themes" page of the "Deserts and Desertification: Challenges and Opportunities" conference web site explains:
True deserts (arid and hyper-arid drylands) are typically not the areas in which land degradation, erosion, and other manifestations of desertification take place. In spite of their inhospitable image, deserts provide unique opportunities for human endeavors. Non-desert drylands, on the other hand, are prone to degradation by human activities. The challenge facing humanity, therefore, is to develop these drylands sustainably without causing desertification. (2)
Understanding how drylands soils work is a fundamental step towards meeting this challenge. Jeff Silvertooth's article provides an introduction to two potential soil characteristics widely found in drylands: salinity and sodicity. Since both of these characteristics can have serious and adverse effects on soil's ability to support vegetation, a good grasp of these basics is useful to backyard gardeners as well as to large-scale agronomy.
Problems such as soil salinity and sodicity have plagued farmers since the advent of agriculture; irrigation-induced soil salinity, for example, played a role in the ultimate collapse of the ancient "Fertile Crescent" civilizations of Sumer and Babylon. A much more recent problem is the excessive production of greenhouse gases that contribute to global climate change. Among the most important of these gases is carbon dioxide, and carbon sequestration in vegetation and soil is one potential mitigation strategy being vigorously explored in a number of drylands locations, including rangelands. Gyami Shrestha reports on a study that examined the effects of 40 years of grazing exclusion in semi-arid Wyoming, USA, on soil organic carbon and soil microbial biomass carbon (both of which are indicators of overall soil health). By leading to a better understanding of the complex web of interactions between climate, soil, vegetation and grazing pressure, such studies can potentially help livestock and rangelands managers to plan grazing in ways that will provide environmental as well as economic benefits.
In his article, Arun K. Sharma makes the case for promoting and developing small-scale organic farming systems in the semi-arid drylands of India. He advocates linking traditional farming practices with modern science to create farming systems that will not only enhance local food security and livelihoods but also promote soil health and biodiversity. He also stresses the importance of stakeholder participation and local "ownership" of implemented solutions (that is, the bottom-up approach) as a necessary condition for such solutions to be sustainable in the long term. As Sharma makes clear, both traditional and scientific knowledge are amply available with regard to Indian drylands; still needed, though, are better development of supportive policies at local, state and national levels, and stronger collaboration among all interested stakeholders.
Finally, Petra Tschakert, in a case study from a soil carbon sequestration project in drylands Senegal, provides an excellent example of an approach that carefully blended traditional systems, science, and local buy-in, with positive local results. In this follow-up to a previous article written for ALN (3), Tschakert reports on the social learning dimensions of this project. The model followed throughout the project was that of "knowledge partnerships," combining local environmental wisdom with science-based knowledge in order to promote sustainable soil fertility management. The results are encouraging, and suggest a general approach that could potentially be replicated in drylands carbon sequestration projects elsewhere.
(2) This international conference will be held from November 6-9 2006 at the Sede Boquer campus of Ben Gurion University of the Negev, Israel; for more information see: http://www.desertopportunities.org/ (back to text)
(3) Tschakert, Petra. 2001. Human dimensions of carbon sequestration: A political ecology approach to soil fertility management and desertification control in the Old Peanut Basin of Senegal. Arid Lands Newsletter No. 49, May/June 2001: http://ag.arizona.edu/OALS/ALN/aln49/tschakert.html (back to text)
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