Soil conservation options in the Savanna of

West Africa:

new approaches to assess their potential

International Institute of Tropical Agriculture– www.iita.org

Birte Junge

Overview of activities and results of the BMZ/GTZ-Project

conducted at IITA from 2005-2008

- Introduction

Term: Soil

Problem: Soil erosion in Nigeria

- Activities and Results of studies on

1. Remote sensing + GIS

2. Adoption of soil conservation technologies

3. Measurement of erosion

- Conclusions

Outline

Soil conservation (Gibbons 1988)

- includes whole program of studies for preventing + reducing soil degradation

Introduction

Soils in West Africa

- Age: old

- Material: sand / gravel / clay

(Lal 1995)

Luvisol

Ah

2 Bt

3 Ct

Soil degradation (Oldeman 1991)

- Soil erosion by water

- Soil erosion by wind

- Chemical deterioration

- Physical deterioration

Problem: Soil erosion in NigeriaIntroduction

Federal Surveys of Nigeria (1992)

General Soil Erosion Map of Nigeria 1:6,000,000

Sheet erosion

Gully erosion

Wind erosion

Output 1:

Land use intensification in pilot villages varying in length of cropping season

and linkage to erosion features established.

Pilot villages:O1: Methods

Remote sensing data:

Aerial photograph IKONOS QuickBird

Date 1962/1981 2000 2005/06/07

Spatial resolution (panchromatic image): 1 m 0.6 m

O1: Methods

Maize

Millet / Sorghum

Cowpea

Interpretation:

Land use/land cover

O1: Methods

Compound

O1: ResultsBadume: Kano State

Change of village area

Today:

NO land available any more

Total Increase

4022000

An. increase

2651949

Year

+ 137

+ 2.7

Area (ha)

O1: ResultsKayawa: Kaduna State

Change of farmland

1962

Cowpea

Maize

Sept. 2000Dec. 2006

+ 216.4

Change

49.7

1962

+ 20.5286.6266.1Arable land (ha)

Change20062000Year

Gadza:

Change of settlement, forest, uncultivated land

O1: Results

Oct. 2000Jan. 2005

Sorghum Millet Fallow

Rice

- 26.577.5104.0Uncult. Land (ha)

- 4.88.513.3Tree, shrub (ha)

+ 0.31.51.2Settlement (ha)

Change20062000Year

Land use intensification:

O1: Summary

- Reduction, elimination of fallow

- Deforestation

- Decrease of uncultivated areas in surroundings

- Expansion of settlements areas

- Expansion of villages areas

- Expansion of farmland

Rate of increase higher in former times

No expansion possible any more today (land scarcity)

Conversion of other land use types into farmland

O1: ResultsBadume: Kano State

Present gully erosion

2000

Measurement:

7708Soil loss (t)

1.2Area (ha)

2006Year

2006

Calculation:

7.245.137.9Area (ha)

Increase20062000Year

O1: ResultsBadume: Kano State

Future gully erosion

2006

Depth line

Gully border 2006

Gully border 2016

Gully border 2026

Estimation:

R = 0.36 (A)0.46 (P)0.20

R = Rate of headward advancement (m yr-1)

A = Tributary watershed area (ha)

P = Annual precipitation (mm)

Morris and Fan (1997)

Badume: R = 0.5 m yr-1

Year 2006 2016 2026

Area (ha) 4.3 5.1 5.9

1962

O1: ResultsKayawa: Kaduna State

Sheet erosion

Year 1962 2000 Change 2006 Change 2016

Sheet erosion (ha) 7.9 25.6 +17.7 32.3 + 6.7 42.3

Annual rate (ha yr-1) 0.5 1.1

2000

2005

Gadza: Niger State

Gully erosion

O1: Results

River

Settlement

1 m

Year 2000 2005 Change 2015

Gully length (km) 12.8 58.4 + 45.6 91.2

4184Soil loss (t)

1.2Area (ha)

2006Year

Measurement:

Eglime: Dept. Mono

Gully erosion

O1: Results

2007

Cotton

Gully

Year 1982 2000 2007 Change 2017

Gully length (km) ? 4.4 42.4 + 38.0

Gully area (ha) 2.3 18.7

Soil erosion:

O1: Summary

- Reduction of arable land

Decrease of crop production

- Reduction of uncultivated area in surroundings of farmland

Decrease of grazing land

- Increase of gully and sheet erosion in Badume, Kayawa, Gadza, Eglime

Rising conflicts among various users deriving from competition

for limited resources in the future

Use of thematic maps:O1: Conclusions

Agenda 21 (UN 1992)

- more effective use of land and natural resources

by improved planning, management and evaluation systems

Nigerian Department of Agricultural Land Ressources, Abuja

- Implementation of appropriate policies

Environmental Management Support System

- Database for inventory of natural resources

Problems: missing equipment, no trained staff, …

Use of thematic maps:O1: Conclusions

Land use planning

Soil conservation

- Field maps for installation of

soil erosion control measures

Tree, Shrub

Vetiver

Stone barrier

Badume

- Reservation of areas

with fertile soils for farming

with degraded soils for reforestation, settlements

with minerals for mining

Publications:

O1: Outcome

Farmer Field Hour:

Junge B., Alabi T., Sonder K., Abaidoo R., Chikoye D., Stahr K. (2008):

Remote sensing and GIS for monitoring changes of land use/land cover and environmental degradation

in different agroecological zones of West Africa

Manuscript for Int. J. Remote Sensing

Junge, B., Abaidoo, R., Chikoye, D., Alabi, T. & Stahr, K. (2006):

Monitoring of land use intensification and linkage to soil erosion in Nigeria and Benin.

Conference proceedings, Deutscher Tropentag (DTT), 11-13 October 2006, Bonn, Germany

- Presentation of study on land use change

and soil degradation

- Discussion of possible soil conservation

measures

Kayawa 31 Oct. 2007

Output 2:

Impact of soil conservation technologies in the Savanna of Nigeria, Benin,

and Ghana assessed.

Search for literature on soil conservation:

O2: MethodsLiterature

- Internet

- Research Institutes

- Universities

- Gov. organizations

- NGOs

Generation of database:

~ 1200 references

Location for

search

of literature

History of soil conservation in Nigeria:

- Pre-colonial era: indigenous technologies (Slaymaker & Blench 2002)

e.g. ridging, terracing, fallowing

- Colonial era: large-scale projects in areas of high agricultural potential

often failed due to inappropriate technologies

- After 1960: more emphasis put on soil fertility issues

- Today: FGN plans to spend US$ 0.5 mio on soil erosion projects (FGN 2007)

O2: Results

Strategies of soil conservation:

El-Swaify et al. (1982) (changed)

Off Farm strategies

Mechanical Biological

Dams

Waterways

Structures

Wind &

Fire Breaks

Tree

Planting

Planting

Shrubs

& Grasses

Mulching

On Farm strategies

Agronomic

Measures

Soil

Management

Mechanical

Methods

Crop

Management

Conservation

Tillage

Terracing

Waterways

Structures

Erosion control strategies

O2: Results

Esa Oke

Constraints

large amount required: (4-6 t ha-1) Lal (2000)

extra costs for purchase, transport

of brought-in material, labour for

distribution on the fieldLal (1995)

Mulching is a useful SCT

reduces erosion through soil coverageOdunze (2002)

increases infiltration, aggregate stabilityHulugalle et al. (1995)

increases activity of soil faunaTian et al. (1997)

increases level of organic matter, nutrients,

and crop yieldMbagwu (1991)

Benefits

Mulching

O2: Results

Ibadan

Constraints

special knowledge required on

compatible species, spacing to

avoid competition for use of growth

resourcesTarawali et al. (1999)

reduces erosion through canopy cover

and by acting as runoff barrier Lal (1989)

maintains and improves soil structure Tian et al. (1999)

improves ability to recycle nutrients (A)Kang et al. (1995)

Benefits

Crop managementIntercropping, Alley cropping, Cover cropping, Fallowing, Planting pattern...

O2: Results

Crop management is a useful SCT

Badume

M, N:

difficult to perform on shallow land Eziakor (1990)

poor aeration of root/tuber crops

in soils with poor drainageKowal and Stockinger (1973)

R:

reduces soil coverageLal (1989)

Constraints

M, N:

reduces soil loss through soil coverageKirchhof & Salako (2000)

maintains and improves physical, chemical,

and biological soil properties

Osunbitan et al. (2005)

R:

reduces erosion by acting as runoff barrierLal (unpubl.)

improves infiltration by destroying surface

crusts and reducing compactionChiroma et al. (2006)

Benefits

Conservation tillageMinimum tillage, No-till + Ridge Tillage

O2: Results

Specified tillage operations are useful SCT

Modelling to determine areas with potential erosion hazard

Universal Soil Loss Equation (USLE) Igwe (1999)

Other approaches

Remote sensing + GISto monitor erosion within space, time

NIGERIA SAT-1 Ayeni et al. (2004)

IKONOS, QuickBird Junge et al. (unpubl.)

O2: Results

… are useful tools for improving soil conservation

Choice of SCTs in dependence of…

AEZ Mulch. Interc. Coverc. No-till Ridg. TRidg.

Sahel S. X X X X

Sudan S.. X X X X

Guinea S. X X X X

Derived S. X X X X

Humid F. X X X X

Nigeria

Climate:

Soil:

x

x

Interc.

x

x

Coverc.

X

TRidg.

X

Ridg.

X

No-till

xSand

xClay

Mulch.Texture

Site specific choice

O2: Results

Performance of soil conservation:

e.g. Conservation Tillage

Author LocationAina, O.A.; Lal, R. and E.J. Roose (1991) (review)

Amezquita, E., Lal, R., Greenland, D.J. and D. Payne (1993) IITA, Ibadan

Armon, M.N. (1980) IITA, Ibadan

Chiroma, A.M., Yakubu, H. and M.K. Sandabe (2002) University in Maiduguri

Chiroma, A.M., Folorunso, O.A. and A.M. Kundiri (2005) University in Maiduguri

Couper, D.C., Lal, R. & S. Claassen (1980) IITA, Ibadan

Franzen, H., Lal, R. and W. Ehlers (1994) IITA, Ibadan

Juo, A.S.R. (1995) IITA, Ibadan

Kirchhof, A.C. and F.K. Salako (2000) IITA, Ibadan

Lal, R. (1974, 1985, 1997) IITA, Ibadan

Maurya, P. R. and R. Lal (1980) IITA, Onne, Port Harcourt

Ogunremi, L.T. and R. Lal (1986) IITA, Onne

Ogunremi, L.T., Lal, R. and O. Babalola (1986) IITA, Ibadan

Onwualu, A.P. and U.G.N. Anazodo (1989) University in Nsukka

Opara-Nadi, O. A. and R. Lal (1987) IITA, Ibadan

Osunbitan, J.A., Oyedele, D.J. and K.O. Adekalu (2005) University in Ile-Ife

Most of research done on-station

O2: Results

Questions: - experience with implementation of SCTs

Adoption of Soil Conservation Technologies by farmers:

QuestionnaireO2: Methods

Group discussionIndividual interview Field surveyRespondents: 20 farmers per village

(trained + not trained)

Locations:Nigeria: 3 villages

Benin: 4 villages

Ghana: 3 villages

Known SCTs: ▪ Mulching

▪ Intercropping

▪ Cover cropping

▪ Fallowing

▪ Agroforestry

▪ Contour tillage

▪ Cut-off drainage

Reasons:

Practiced SCTs:▪ Mulching

▪ Cover cropping

▪ Contour tillage

▪ Cut-off drainage

Criteria Mulching Cover

cropping

Contour

tillage

Cut-off

drainage

labour intensive

tool available

compatible

easy to learn, practice

no no no yes

yes yes yes no

yes yes yes no

yes yes yes no

O2: ResultsNigeria

Adoption of SCTs: 51 % rejected all SCTs

38 % adopted 1 SCT

10 % accepted 2-3 SCTs

Installation

started

Installation

completed

Mainte-

nance

Implementation

interrupted

Continuity

of adoption

O2: ResultsNigeria

Characteristic rSp

Age - 0.08

Level of education 0.13

No. of memberships in organizations 0.40*

No. of SCTs aware 0.32*

No. of labourer on the farm 0.36*

Total annual income 0.06

Correlation between personal and socio-economic characteristics

and number of SCTs adopted: (* significant at 0.05 level)

Knowledge on SCTs + labourer availability

have positive influence on adoption of SCTs

Characteristic rSp

Age - 0.08

Level of education 0.13

No. of memberships in organizations 0.40*

No. of SCTs aware 0.32*

Characteristic rSp

Age - 0.08

O2: ResultsNigeria

Soil conservation :

Literature review:- Mulching, crop management, conservation tillage are useful SCTs

- Much research on-station, few projects on-farm

Questionnaire:- Mulching, cover cropping, contour tillage adopted by farmers

- Knowledge on SCTs, labour availability influence adoption rate

O2: Summary, Conclusions

Bring SCTs on the farmers’ fields

Bring SCTs to the farmers

Nigeria

Publications:O2: Outcome

Junge B., Deji O., Abaidoo R., Chikoye D., Stahr K. (2008):

Farmers’ adoption of soil conservation technologies:

Examples from a survey in Osun State, Nigeria

Manuscript submitted to J. Agric. Techn. Educ.

Junge B., Deji O., Abaidoo R., Chikoye D., Stahr K.,

Kirchhof, G. (2008):

Overview about soil conservation technologies and their

perception by farmers in Nigeria.

Manuscript submitted to Technical Reports of ACIAR

Junge B., Deji O., Abaidoo R., Chikoye D., Stahr (2007):

Soil conservation in Nigeria: Assessment of past and

present initiatives. Proceedings of AfNet, TSBF,

17-21 September 2007, Arusha, Tanzania, 20 pp.

Output 3:

New approaches for on-farm monitoring of short and long-term benefits

from soil conservation technologies developed and tested.

O3: Methods

Traditional technique: Erosion plots

A23

Campus: A23

- Size: 4 x 20 m

- Slope gradient: 4 %

Advantage:

- Data on runoff, soil loss

- Comparison of different crops

under natural conditions

Measurement of soil erosion

Disadvantage:

- Measurement after each rain

- Time-consuming, labor-intensive,

huge scope for faults

- No data on deposition

O3: Methods

Nuclide 137Cs 7Be

Source nuclear-weapon

tests

spallation of O, N in

tropo-, stratosphere

Fallout began in 1950s,

max. 1963 -1964,

decrease since then

constant over years

Half life 30.2 yr 53.3 d

Soil redistr.

medium-term short-term

Measurement of soil redistribution

- rapidly, strongly adsorbed by fine soil particles

- distributed across surface by physical processes

- valuable sediment tracer(Zapata 2002)

Advantage:

- Data on erosion, deposition

at different time scales

- Min. disturbance of sites

Disadvantage:

- No data on runoff

Alternative: Radionuclide technique

IKONOS

2000

Field trial 2007: LocationO3: Methods

Alternative: Radionuclide technique

Reference Site- No soil movement

Forest

Arable land- Soil erosion + deposition

BS16

5 cmCore

Coring Method

Field trial 2007: SamplingO3: Methods

Reference Site Arable land

Vertical distribution

Ridge

Furrow

Slope (5%)

Spatial distribution

Topsoil + sediment

Field trial 2007:O3: Results

Reference Site Arable land

- max. concentration below surface

- gradually decrease with depth

Y = 38.1 (1-0.55x)

R2 = 0.9

Vertical distribution

Spatial distribution

Range 403.0 - 839.6 Bq m-2

Mean 569.3 150.1 Bq m-2

(n = 9)

Range 96.9 - 1494.4 Bq m-2

Mean 496.3 272.5 Bq m-2

(n = 44)

- uniform concentration in ploughed layer

Field trial 2007:O3: Results

Arable land

Particle size dependence

- increase of 137Cs concentration

with decreasing particle size

B = soil bulk density (kg m-3)

d = depth of cultivation layer (m)

P = ratio of 137Cs in mobilized sediment to that of original soil

P’= ratio of 137Cs in deposited sediment to that of mobilized sediment

T = time elapsed since the initiation of 137Cs accumulation (yr)

X = % reduction in total 137Cs inventory (Bq m-2)

X’= % increase in total 137Cs inventory (Bq m-2)

Y = mean annual soil loss rate (t ha-1 yr-1)

Y’= mean annual deposition rate (t ha-1 yr-1)

O3: Methods, Results

Proportional model (Walling and He 1997)

Field trial 2007:

YBdX

TP10

100Y

BdX

TP10

100YBdX

TP10

100Y

BdX

TP10

100YBdX

TP10

100Y

BdX

TP10

100

YBdX

TP10

100

PT

XBdY

10010

Conversion Model

to convert radionuclide inventories (Bq m-2) to erosion/deposition rate (t ha-1)

Lower slopeMiddle slopeUpper slopePosition

-155.6

Total

-29.0

3

-23.9

2

-18.3

1

-10.6

6

-18.2

5

-19.7

4

-10.7

9

-3.1

8

-7.3

7

Rate(t ha-1 yr-1)

Sampling

point

Balance1110

-14.8 -148.5+7.1

Lal (1976): soil loss 43.5 - 156.2 t ha-1 yr-1

Ongoing Activities

Poster

Junge, B., Dercon G., Walling D., Abaidoo, R., Chikoye, D. & Stahr, K. (2008):

Use of the 137Cs technique under tropical conditions: Estimation of medium-term soil redistribution rates

in Ibadan, Nigeria. EUROSOIL, 25-29 August 2008, Vienna, Austria

Publications:

Field trial 2008: in cooperation with IAEA, Austria

Measurement of

Medium-term soil redistribution (137Cs) - Onigambari, 50 km S Ibadan

Short-term soil redistribution (7Be) - Campus, A23

O3: Outcome

1. Remote sensing + GIS

What is going on?

Why is it going on?

2. Adoption study

What can be done?

How can it be done?

3. Measurement of soil erosion

Does it work in the tropics?

→ Contribution to soil conservation in the savanna of West-Africa

BMZ/GTZ-Project:

WHO does it?

Conclusions

Robert

Tunrayo, Kai, Subash

Diakalia, Olanike, Sam

Sunday

Computer

Ibrahim, Jean, Michael