presented at the 13th World Water Congress, Montpelier, France

1. Isabelle Terrasson1, Myles
Fisher2, Winston Andah3, and
Jacques Lemoalle1
1 Institut de Recherche pour le Développement (IRD), Montpellier, France.
2 Comidas Limitada (COMIL), Cali, Colombia.
3 Water Research Institute (WRI), Accra, Ghana.

2. Where is the Volta Basin?
What are the problems?
How did we investigate them?
What were the answers?

3. • Where is the Volta Basin?

4. Maize Millet Sorghum
Area (millions ha) 1.5
1.0
0.5
0.0
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Year

5. Low actual productivity
Low water productivity
The isohyets moved south
1 to 1-1/2 degrees around
1970, but have stabilized
there.

7. Sudano-Sahelian zone: 601mm<Pmoy<900mm
WP(kg/m3)
0,50 Sudanian zone: 901mm<Pmoy<1100mm
0,45 Guinean zone: Pmoy>1100mm
2
0,40 R = 0,0329 Linéaire (Sudano-Sahelian zone:
601mm<Pmoy<900mm)
2
R = 0,1134 Linéaire (Sudanian zone:
0,35 2 901mm<Pmoy<1100mm)
R = 0,248 Linéaire (Guinean zone: Pmoy>1100mm)
0,30
0,25
0,20
0,15
0,10
0,05
0,00
P(mm)
400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

8. Selected seven sites on a S-N transect on
the meridian of Ouagadougou, Burkina
Faso.
Sites 1.5˚ (~150 km) apart (6.3˚ - 15.3˚N).
9 soils in 3 groups:
• Coarse sands
• Fine sands and sandy loam
• Loams

9. • Ouagadougou Meridian Transect

10. For each site, we generated 99 years
weather data for each using MarkSim
(climate normal data from WorldClim).
3 crops
• Maize (W African commercial variety)
• Millet (Local variety)
• Sorghum (cv Hegari, W African variety)
Simulated growth of crops using DSSAT
models:
• 3 crops*9 soils*7 sites*±fertilizer*99 years

11. Within each crop, for each site, soil, and
fertilizer combination we ranked yields
and plotted :
Median yields
• Indicate agronomic potential, half years yield
less than median and half yield more
20 percentile yields
• Indicate risk, yield equal or better four years in
five ( worse one year in five).

12. Agronomic potential

13. Latitude
Coarse sand Fine sand/sandy loam Loam

14. Latitude
Coarse sand Fine sand/sandy loam Loam

15. Risk

16. Latitude
Coarse sand Fine sand/sandy loam Loam

17. Latitude
Coarse sand Fine sand/sandy loam Loam

18. Fertilizer boosts yields, but is too risky
at higher latitudes (Ouagadougou and
north).
The yield increase with fertilizer is
dramatic on the coarse, sandy soils at
low latitudes.
At low latitudes, fertilizer is the answer,
especially on poor soils (N leaching).

19. At high latitudes drought is the problem.
Farmers use sparse planting to avoid risk.
The yields are always low, but reliably low
with minimum investment.
Climate change:
• Overall climates will be more variable , hence more
risky
• Will move the isohyets:
Drier will move the curves to the left (more risky)
Wetter will move the curves to the right (less risky).

20. Better management of water from rainfall
(increased infiltration: bunds, planting
pits, etc.)
Micro-doses of fertilizer.
Small scale irrigation to overcome within
season drought (small-scale dams,
treadle pumps).