By Dr. Leigh Winowiecki, Soil Scientist
Center for Tropical Agriculture (CIAT), Sustainable Land Management Program, based in Nairobi, Kenya.
Land degradation is increasingly recognized as a major cause of low agricultural productivity, loss of biodiversity, and poverty. When degraded lands are continuously cultivated without rehabilitation or conservation measures, they can become irreversibly unproductive. This has negative environmental and socio-economic consequences. Understanding the underlying causes of land degradation has become important for the design of strategic rehabilitation measures.
As a first step in addressing these challenges, we need to understand where degraded lands occur and the severity of this degradation across landscapes. Systematic biophysical field surveys are needed to fill this knowledge gap, to assess and integrate landscape-level attributes and processes.
The Africa Soil Information Service (AfSIS) project employs the Land Degradation Surveillance Framework (LDSF) to conduct biophysical baseline surveys at 60-100 sq. km sentinel sites, stratified by Koeppen-Geiger climatic zones, across sub-Saharan Africa. The LDSF framework is designed for practical, timely and cost-effective soil and ecosystem health surveillance, and in particular for mapping soil condition. It is also designed for monitoring changes over time, and provides opportunities for better targeting of improved soil management. The data collected are used to develop models for predicting landscape attributes in unsampled areas. The Surveillance Framework is unique in that it systematically assesses several ecological metrics simultaneously at four different spatial scales, making it a spatially stratified, hierarchical sampling design.
Four AfSIS sentinel sites were completed in Ethiopia between February and June 2011 (Figure 1). Dr. Assefa Abegaz, professor of Soil Science at Addis Ababa University was designated as AfSIS Ethiopia National Coordinator. Scientists from Addis Ababa University and Mekelle University led the field surveys, assisted by CIAT-AfSIS drivers and field assistants. Local woreda (agricultural extension agents) were involved at each of the sites.
These four sites are characterized as mixed crop-livestock systems and include the cultivation of teff, wheat, sorghum and barley while allowing land for goats, donkeys and camels.
The Ethiopia surveys identified high erosion prevalence with almost 100% probability of erosion risk at three of the four sites. Low overall tree densities were also observed, with three of the four sites having an average of less than 50 trees per hectare. The Kutaber site is dominated by exotic tree species. Additional analyses include the assessment of root depth restrictions, infiltration capacity, and soil organic carbon stocks.
Preliminary estimates of soil organic carbon concentrations indicate low organic matter reserves, which could negatively impact agricultural productivity and increase land degradation risk. Consistent methodology used across landscapes allows for direct comparisons and the creation of robust models.
Interactions with the local people around Kutaber highlighted the need for better land management techniques regarding soil conservation, animal stocking densities, and water harvesting activities. By addressing land management issues and constraints, the livelihoods of the local people of Kutaber could also be improved.
What is next? These surveys are part of a larger effort to predict and map land degradation risk across 18.1 million sq. km of sub-Saharan Africa. This initiative, along with other analyses, will help us to develop maps of soil functional properties and better understand the dynamics of other important ecological indicators, including agricultural productivity. Ultimately, the information obtained from these analyses will help improve land management in order to preserve soil health and the livelihoods that depend on the land’s productivity.