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Knowledge gaps trees, deep soil resources and rainfed crop production in dryland
production systems
Jan de Leeuw ICRAF Nairobi
Revival of interest groundwater in Africa
• 2012 UCL Research 'Huge' water resource exists under Africa
• NERC-UPGRO: Unlocking Potential of Groundwater in Sub Saharan Africa
• Renewed interest in development of irrigated agriculture
• Argument this should not compromise benefits from agroforestry systems
Perspectives on Agriculture in Sahelo Soudanian Zone
• Crops – sorghum millet farming system• Livestock – pastoral / agro-pastoral systems • Trees – dryland agroforestry system
• Mixed systems: annual crops, livestock and trees
• Agricultural institutions (incl. research) focus on crops and livestock
• Do trees merit more attention?
Commodity based perspectives
• Agendas agriculture achieving DG’s
• Leading to focus agricultural institutions on crop and livestock commodities
• Negative side– Monocultures – diet and health – Barren unhealthy landscapes – Unsustainable natural resource management
Trees and multifunctional systems • Agricultural systems can be managed to include trees to optimize
provisioning of multiple functions:
– Water and nutrients– Dietary diversity– Healthy human habitat– Food security / resilience– Sustainability
• Trees build many of these traits into agricultural production systems, some are direct many are indirect benefits
• Ecosystem service perspective on benefits from trees – Provisioning services, food and other goods– Supporting and regulating services
The ecosystem goods: tree products
• Positives – – Production of tree products more resilient to drought
than crops or livestock – Food fruits, nuts, edible oils also available dry season – Construction- and fuel-wood, gum arabica, assets than
can be used in case of shortage
• Negatives – – Prone to over-utilization and degradation– Trees in the landscape are a fragile natural capital
Regulating service: Trees and groundwater
• Hydraulic lift and redistribution groundwater
• Driven by gradient in water potential
• Moisturizing dry upper soil horizons
• Benefiting shallow rooted species like crops
Supporting service: trees and soil fertility • Nitrogen fixation associated to roots and moisture • Redistribution nutrients from lower soil horizons
Example Faidherbia alibida
• Groundwater dependent in drylands • Widespread in Africa• 5 million ha in Niger• 0.5 million ton increased cereal production • 1 million people benefiting • Are these benefits attributable to groundwater? • What is the potential for upscaling and how does
that relate to groundwater?
Knowledge gaps nutrient enrichment and hydraulic redistribution
• Biophysical principles well understood• Significance and benefits of poorly not quantified • Potential for designing more resilient agricultural
systems to be explored
Trees and crops
• Positive impact on crop production – Water balance – shade, hydraulic redistribution – Nutrients – Upward redistribution, N fixation
• Negative impacts on crop production – Competition for water and nutrients
• Gap - optimal design of tree - crop systems
Trees and livestock
• Positive impacts – – Food - foliage and seeds as forage for livestock – Veterenary medicine – trees important
• Negative impacts – – Livestock degradation tree cover and the sustainability of
benefits derived from trees
• Gap – designing sustainable integration of tree based forages and crop residues in livestock production systems
Need for a strategic perspective on groundwater and evergreen agriculture
• Reawakened interest developing groundwater and irrigation
• Danger of development of irrigated agriculture ignoring benefits from AF systems
• Blue water paradigm dominates groundwater management
• Paradigm shift required towards blue and green water management
• Evidence required that trees in Sahelian landscapes generate significant social benefits
Take home messages
• Trees enhance the production of the system as a whole, benefits of this poorly recognized
• Trees system builders, multifunctional landscapes with many desirable traits including support to crop and livestock production
• Research lacking on optimization and design of multifunctional landscapes and the role of trees in there