CA potential effects on soil erosion for rainfed crops in the Lake Alaotra region in Madagascar. Eric Scopel

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CA potential effects on soil erosion for rainfed crops in the Lake Alaotra region in Madagascar. Eric Scopel

  1. 1. Conservation Agriculture potential effects on Soil Erosion for rainfed crops in the Lake Alaotra region in MadagascarL.I. Rasolofo, F. Van Hulst, K. Naudin, R. Domas, J. De Graaff,S. Visser, E. Scopel
  2. 2. Alaotra Lake: One of the main zones of rice production in MadagascarRice mainly under irrigated conditions in the lowlands, but with strong progress of upland rice on the hillsides with other stapple crops
  3. 3. Rainfall variability: A strong constraint for rainfed crops Rainfall at Alaotra Lake 1600.0 1999-2000 1400.0 2000-01 1200.0Rainfall in mm 2001-02 2002-03 1000.0 Total moy 11 ans 800.0 2003-04 600.0 2004-05 2005-06 400.0 2006-07 200.0 2007-08 2008-09 0.0 2009-10 sep oct nov déc jan fév mars avr mai juin juil août month Distribution
  4. 4. Classical problems with conventional tillage
  5. 5. CA as been promoted as an alternative for sustainable production of rainfed stapple crops- First on maize and grain legumes crops- Then with new adaptations for rainfed uplandrice
  6. 6. Effect of cover crops and mulch on water balance and soil erosion
  7. 7. Water erosion: EXPERIMENTS Madagascar Lb R N O E P6 6m P5 6m P4 6,5mP= + /- 25% S 3m 18 17 16 15 14 13 12 11 10 P3 P2 P1 SCV R P= + /- 6% 9 8 7 6 5 4 3 2 1 6,5m 6m 6m CA system with Ploughed CA maize+dolichos system with System with intercropped rainfed rice rainfed rice or or or SCV M+D Lb R SCV R SCV M+D
  8. 8. Soil losses 300 c Soil losses (g/m²) 250 P.terres (g/m²) 200 150 bDivided by 100 a Divided by 2 to a 50 a a 4 to 4 8 0 Lb R SCV R SCV LB R SCV R SCV M+D M+D Pente Slope 25% Faible 6% Slope Pente Forte Important difference on soil losses between ploughed system and AC systems This difference increases when the slope increases
  9. 9. Relation between the ground cover rate and the water erosion Pente faible Pente faible 9 Pente forte 450 Pente forte 8 R²= 0,740 (pente faible) 400 R²= 0,823 (pente forte) 7 R²= 0,929 (pente forte) 350T. ruis (%) P.terres (g/m²) R²= 0,954 (pente faible) 6 300 5 250 4 200 3 150 2 100 1 50 0 0 0 20 40 60 80 100 120 0 20 40 60 80 100 120 T.couv(%) T.couv(%) Relation between cover rate and Relation between cover rate and runoff soil losses
  10. 10. Nutrients losses: N, P, K, C Ploughed Nutrients losses system CA system saved around: 2 kg N/ha 13 kg P/ha 0,7 kg K/ha 57 kg C/ha DMC systems Proportional to soil erosionReduced losses but linked with low rainfall of 2010-2011 cycle(-40%: 640 mm)
  11. 11. First uses of RUSLE for extrapolating effects of Conservation Agriculture on erosion
  12. 12. The model• Soil loss A = R · K · LS · C · P• Rainfall erosivity R potential• Soil erodibility K erosion• Slope length & steepness LS• Crop cover C effect of• Conservation practices P management
  13. 13. Estimation of the C factor: pluri-anual rotations Maize Dolichos lablab Weeds Upland rice Stylosanthes guianensis
  14. 14. Estimation of the C factor: combining mulch and plant cover
  15. 15. Pluri-anual effects of CA on erosion Cropping system Year Soil loss from monthly cover management C (ton·ha-1yr-1) Stylo 1 1 7.2 2 0.1 3 0.2 4 0.5 Av. 2.0 Dolichos 1 7.3 2 10.6 Av. 9.0 Traditional 1 79 2 94.1 Av. 86.6
  16. 16. Main conclusions• Strong inter-annual variability linked with climate variability in this kind of region• Necessity of considering for CA both mulch and crops in their function of soil surface protection• Necessity of taking into account rotations of the CA Systems in their diversity (pluri-annual scale)• The importance of having a diverse rotation pattern with cover crops (directly covering soil, indirectly by producing biomass for mulch)
  17. 17. Misaotra, Thank you, Merci

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