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

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

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200.0

400.0

600.0

800.0

1000.0

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1600.0

sep oct nov déc jan fév mars avr mai juin juil août

Ra

infa

llin

mm

month

Rainfall at Alaotra Lake

1999-2000

2000-01

2001-02

2002-03

moy 11 ans

2003-04

2004-05

2005-06

2006-07

2007-08

2008-09

2009-10

Rainfall variability:A strong constraint for rainfed crops

Total

Distribution

Classical problems with conventional tillage

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

Effect of cover crops and mulch on

water balance and soil erosion

N

S

P= +/- 25%

O E6m 6m 6,5m

3m

6,5m 6m 6m

P= +/- 6%

12 11 1015 14 1318 17 16

3 2 16 5 49 8 7

Water erosion: EXPERIMENTS Madagascar

Ploughed system withrainfed rice

or Lb R

P1

P5

Lb R

P3

P4

CA system withmaize+dolichos

intercroppedor

SCV M+D

SCV M+D

P2

P6

CA System withrainfed rice

or SCV R

SCV R

0

50

100

150

200

250

300

Lb R SCV R SCV

M+D

LB R SCV R SCV

M+D

Pente Faible Pente Forte

P.t

err

es (

g/m

²)

aa

a

c

b

aDivided by 4 to 8

Divided by2 to

4

Soil losses

Important difference on soil losses between ploughed system and AC systemsThis difference increases when the slope increases

25% Slope 6% Slope

Soil

loss

es(g

/m²)

Relation between the ground cover rate and the water erosion

Relation between cover rate and

runoff

Relation between cover rate and

soil losses

0

1

2

3

4

5

6

7

8

9

0 20 40 60 80 100 120

T.couv(%)

T.

ru

is (

%)

Pente faible

Pente forte

R²= 0,740 (pente faible)

R²= 0,929 (pente forte)

0

50

100

150

200

250

300

350

400

450

0 20 40 60 80 100 120

T.couv(%)P

.terr

es (

g/m

²)

Pente faible

Pente forte

R²= 0,823 (pente forte)

R²= 0,954 (pente faible)

Ploughedsystem

DMCsystems

Nutrients losses: N, P, K, C

Proportional to soil erosion

CA system saved around:

2 kg N/ha13 kg P/ha0,7 kg K/ha57 kg C/ha

Nutrients losses

Reduced losses but linked with low rainfall of 2010-2011 cycle (-40%: 640 mm)

First uses of RUSLE for extrapolating effects of

Conservation Agriculture on erosion

The model

• Soil loss A = R · K · LS · C · P

• Rainfall erosivity R

• Soil erodibility K

• Slope length & steepness LS

• Crop cover C

• Conservation practices P

potentialerosion

effect of management

Dolichos lablab

Weeds

Upland rice

Stylosanthesguianensis

Maize

Estimation of the C factor: pluri-anualrotations

Estimation of the C factor: combiningmulch and plant cover

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

Pluri-anual effects of CA on erosion

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)

Misaotra, Thank you,

Merci