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.3Water Research Institute (WRI), Accra, Ghana.

��Where is the Volta Basin?Where is the Volta Basin?

��What are the problems?What are the problems?

��How did we investigate them?How did we investigate them?

��What were the answers?What were the answers?

•• Where is the Volta Basin?Where is the Volta Basin?

0.0

0.5

1.0

1.5

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Year

Area (millions ha)

Maize Millet Sorghum

��Low actual productivity Low actual productivity ��Low water productivityLow water productivity��The isohyets moved south The isohyets moved south 1 to 11 to 1--1/2 degrees around 1/2 degrees around 1970, but have stabilized 1970, but have stabilized there.there.

R2 = 0,0329

R2 = 0,1134

R2 = 0,248

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

P(mm)

WP(kg/m3)Sudano-Sahelian zone: 601mm<Pmoy<900mm

Sudanian zone: 901mm<Pmoy<1100mm

Guinean zone: Pmoy>1100mm

Linéaire (Sudano-Sahelian zone:

601mm<Pmoy<900mm)

Linéaire (Sudanian zone:

901mm<Pmoy<1100mm)

Linéaire (Guinean zone: Pmoy>1100mm)

��Selected seven sites on a SSelected seven sites on a S--N transect on N transect on

the meridian of Ouagadougou, Burkina the meridian of Ouagadougou, Burkina

Faso.Faso.

��Sites 1.5Sites 1.5˚̊ (~150 km) apart (6.3(~150 km) apart (6.3˚̊ -- 15.315.3˚̊N).N).

��9 soils in 3 groups:9 soils in 3 groups:

•• Coarse sandsCoarse sands

•• Fine sands and sandy loamFine sands and sandy loam

•• LoamsLoams

•• Ouagadougou Meridian TransectOuagadougou Meridian Transect

�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

�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).

Agronomic potential

Coarse sand LoamFine sand/sandy loam

Latitude

Coarse sand LoamFine sand/sandy loam

Latitude

Risk

Coarse sand LoamFine sand/sandy loam

Latitude

Coarse sand LoamFine sand/sandy loam

Latitude

�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).

�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).

�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).