Yields and water productivity of rainfed crops in the Volta basin (West Africa)

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

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Yields and water productivity of rainfed crops in the Volta basin (West Africa)

  1. 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. 2. Where is the Volta Basin? What are the problems? How did we investigate them? What were the answers?
  3. 3. • Where is the Volta Basin?
  4. 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. 5. Low actual productivity Low water productivity The isohyets moved south 1 to 1-1/2 degrees around 1970, but have stabilized there.
  6. 6. 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
  7. 7. 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
  8. 8. • Ouagadougou Meridian Transect
  9. 9. 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
  10. 10. 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).
  11. 11. Agronomic potential
  12. 12. Latitude Coarse sand Fine sand/sandy loam Loam
  13. 13. Latitude Coarse sand Fine sand/sandy loam Loam
  14. 14. Risk
  15. 15. Latitude Coarse sand Fine sand/sandy loam Loam
  16. 16. Latitude Coarse sand Fine sand/sandy loam Loam
  17. 17. 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).
  18. 18. 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).
  19. 19. 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).

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