Effect of the ACN on agricultural field water balance in Mali

K. Brannan, R. Kablan, R.S. Yost, M.D. Doumbia, A. Yoroté, Y. Toloba, S. Sissoko, and

M. Vaksman

Overview

• Background

• Hypothesis

• Calculation Methods

• Results

• Future Plans (This was 1st year)

Background(Problems)

Deforestation

Reduced Soil Fertility

Farming on Steep Slopes

Runoff Management

$Revenue Sources$

Reduced Groundwater Recharge

Background(Runoff Management, Mali)

Practice: Amenagement en courbes de niveau (ACN)

• Field Water management practice

• Series of ridges contour

• Permanent Ridge (Ado)

• Temporary Ridges (cropped areas)

• Water management of whole area

• Socio-economic factors

Impact of Practice

No ACN with ACN

Hypothesis

• ACN improves field water balance

• More water available for crop use

• More potential local groundwater recharge (drainage)

• Reduces surface runoff

Approach

• Two Locations (Konkgougou and Fransirokoro)

• Treatments: Field with ACN and without

• Measure Soil Water at multiple locations and depths

• Rainfall and potential evaporation data

• Calculate field water balance

Soil Water Probe

Diviner 2000®, Sentek

Study Site: Konkgougou

Tubes

Permanent Ridges

Field Water Balance

Rainfall

Root ZoneRunoff

Soil WaterStorageDrainage

ET and Evaporation

RainfallRainfallRainfall

Root ZoneRunoff

Soil WaterStorageDrainage

ET and Evaporation

Root ZoneRunoff

Soil WaterStorageDrainage

ET and Evaporation

Field Water Balance

S = R – ET – Esoil – GWR – ROwhere,

S - change in soil water storage

R - rainfall

ET - crop evapotranspiration

Esoil - evaporation from the soil

GWR - local groundwater recharge

RO - surface runoff

Measured

Estimated

Calculated

Field Water Balance: Runoff

RO = R – ET – Esoil – GWR – S

Rainfall and Evaporation

• Rainfall data collected at site

• Potential Evaporation data from Bamako Station

• Soil evaporation constant proportion of potential evaporation

ET Calculation

ETc- Crop evapotranspiration

Kc - crop coefficient

ETo- observed (reference crop) ET

(Kc temporally distributed based on LAI)

occ ETKET

ET Calculation

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Cro

p C

oe

ffic

ien

t (K

c)

Corn Sorghum Millet

Soil Moisture Storage

Root Zone

Drainage

0-70 cm

Transition Zone70-90 cm

Root Zone

Drainage

0-70 cm

Transition Zone70-90 cm

Root Zone

Drainage

0-70 cm0-70 cm

Transition Zone70-90 cm

Integrate Readings

Soil Moisture Storage

0

20

40

60

80

100

120

140

160

180

200

18-Jun 28-Jun 8-Jul 18-Jul 28-Jul 7-Aug 17-Aug 27-Aug 6-Sep 16-Sep 26-Sep

Cu

mm

ula

tive

So

il M

ois

ture

in R

oo

t Z

on

e (m

m)

-30

-20

-10

0

10

20

30

40

S

(m

m)

Local Groundwater Recharge(Drainage)

• Pedo-transfer function

• Van Genutchen’s Equation– Hydraulic potential– Hydraulic conductivity

• Darcy’s Equation

Local Groundwater Recharge

Root Zone

Drainage

0-70 cm

Transition Zone70-90 cm

Root Zone

Drainage

0-70 cm

Transition Zone70-90 cm

Root Zone

Drainage

0-70 cm0-70 cm

Transition Zone70-90 cm

Aggregate

Local Groundwater Recharge

0

0.2

0.4

0.6

0.8

1

1.2

1.4

18-Jun 28-Jun 8-Jul 18-Jul 28-Jul 7-Aug 17-Aug 27-Aug 6-Sep 16-Sep 26-Sep

-50

0

50

100

150

200

8-Jul 18-Jul 28-Jul 7-Aug 17-Aug 27-Aug 6-Sep 16-Sep 26-Sep

Cumulative Local Groundwater RechargeUnsaturated Hyd Cond.

Runoff

RO = R – ET – Esoil – GWR – S

Results

• Comparisons tubes with and without ACN– Tubes 03 to 10– Tubes 05 to 10– Tubes 15 to 21– Tubes 17 to 22

Results: Tubes 03 to 10

Drainage

Runoff

ACN (Tube 03)

Control (Tube 10)

0%

10%

20%

30%

40%

50%

60%

70%

% o

f T

ota

l Rai

nfa

ll

ACN (Tube 03) Control (Tube 10)

Results: Tubes 05 to 10

Drainage

Runoff

ACN (Tube 05)

Control (Tube 10)

0%

10%

20%

30%

40%

50%

60%

70%

% o

f T

ota

l Rai

nfa

ll

ACN (Tube 05) Control (Tube 10)

Results: Tubes 15 to 21

Drainage

Runoff

ACN (Tube 15)

Control (Tube 21)

0%

10%

20%

30%

40%

50%

60%

70%

% o

f T

ota

l Rai

nfa

ll

ACN (Tube 15) Control (Tube 21)

Results: Tubes 17 to 22

Drainage

Runoff

ACN (Tube 17)

Control (Tube 22)

0%

10%

20%

30%

40%

50%

60%

70%

% o

f T

ota

l Rai

nfa

ll

ACN (Tube 17) Control (Tube 22)

Location Effect

Ados

Tube 05

Tube 17Water Accumulates

Future Plans

• Continue data collection(several more years)

• Relate balance to crop yields

• Improve instrument calibration

• Improve calculation methods

• Quantify impact on village wells

• Improve/Modify ACN design

Merci