1. Knowledge gaps trees, deep soil resources
and rainfed crop production in dryland
production systems
Jan de Leeuw
ICRAF Nairobi

2. 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

3. 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?

4. 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

5. 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

6. 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

7. 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

8. Supporting service: trees and soil fertility
• Nitrogen fixation associated to roots and moisture
• Redistribution nutrients from lower soil horizons

9. 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?

10. 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

11. 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

12. 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

13. 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

14. 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