1. Conservation Agriculture potential effects on
Soil Erosion for rainfed crops in the Lake
Alaotra region in Madagascar
L.I. Rasolofo, F. Van Hulst, K. Naudin, R. Domas, J. De Graaff,
S. Visser, E. Scopel

2. Alaotra Lake:
One of the main zones of rice production
in Madagascar
Rice mainly under irrigated conditions in the lowlands, but with strong
progress of upland rice on the hillsides with other stapple crops

3. Rainfall variability:
A strong constraint for rainfed crops
Rainfall at Alaotra Lake
1600.0
1999-2000
1400.0
2000-01
1200.0
Rainfall 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. Classical problems with conventional tillage

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 upland
rice

6. Effect of cover crops and mulch on
water balance and soil erosion

7. Water erosion: EXPERIMENTS Madagascar
Lb R
N
O E
P6
6m P5
6m P4
6,5m
P= + /- 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. Soil losses
300
c
Soil losses (g/m²) 250
P.terres (g/m²)
200
150 b
Divided 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. 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) 350
T. 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. 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 erosion
Reduced losses but linked with low rainfall of 2010-2011 cycle
(-40%: 640 mm)

11. First uses of RUSLE for extrapolating effects of
Conservation Agriculture on erosion

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. Estimation of the C factor: pluri-anual
rotations
Maize
Dolichos lablab
Weeds
Upland rice
Stylosanthes
guianensis

14. Estimation of the C factor: combining
mulch and plant cover

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. 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. Misaotra, Thank you,
Merci