Soil organic carbon dynamics, functions and management in West African agro-ecosystems Bationo A., Vanlauwe B., Kihara J. and Kimetu J.

Soil organic carbon dynamics, functions and management in West African agro-ecosystems

Bationo A., Vanlauwe B ., Kihara J. and Kimetu J.

Outline

• Introduction

• Variability of soil organic carbon content at agro-ecosystem and farm level.

• Effect of soil and crop management on soil organic carbon

• Role of organic amendments on land productivity

• Future research challenge with emphasis on organic matter quantity and quality

• Conclusion

Lack of Resources

Lack of Knowledge

Land Degradation

ImprovedKnowledge

Improved Soil Management

Improved Livelihoods

Virtuouscycle

Viciouscycle

The Vicious and Virtuous cycle

The growth rate for cereals grain yield is about 1%

while population growth is about 3%. During the last

35 years, cereals production per capita has

decreased from 150 to 130 kg/person, whereas in

Asia and Latin America an increase from about 200

to 250 kg/person have been observed. Both labor

and land productivity are among the lowest of the

world.

Per Capita food production declined by about 30%

and cereal self-sufficiency from 85 to 65%

Introduction…

Introduction…

Annual cereal deficit in sub-Saharan Africa amounts to 100 million tons

Food imports increased by about 185% between 1974 and 1990, food aid by 295%

The food gap (requirements minus production) is widening

The average African consumes only about 87% of the calories needed for a healthy and productive life

Introduction … 16% of Africa’s current arable land base is so eroded

that it cannot be useful any longer agriculturally

70% of deforestation is caused by farmers who in their quest for food have no incentive to ponder long-term environmental consequences

Increase in area under food crop in sub-Saharan Africa was mainly due to use of marginal lands hence further environmental degradation through soil erosion and nutrient mining

Increase in yield has been more due to land expansion than to crop improvement potential

Crops Area Yield Production

Cassava 2.6 0.7 3.3

Maize 0.8 0.2 1.0

Yam 7.2 0.4 7.6

Cowpea 7.6 -1.1 6.5

Soybean -0.1 4.8 4.7

Plantain 1.9 0.0 2.0

Based on three-year average for 1988-1990 and 1998-2000. FAO database.

Growth rate of millet 1979-1994

Country Area

(%)/year

Yield

(%)/

year

Production

(%)/year

Production/ hbt (%)/year

WA 4.7 - 0.4 4.2 1.2

Mali 5.1 - 1.0 4.0 2.3

Niger 3.9 - 1.0 2.8 - 1.3

Nigeria 7.7 - 2.3 5.2 2.2

B.F 3.8 2.0 5.9 3.0

Percentage chances in soil fertility parameters in farmers’ fields as a result of 50 years of cultivation in

the Savannah zones

Source: Balasubramanian et al. 1984

Zones Exchangeable cations

Ca Mg K pH

Sudan 21 32 25 4.0

N. Guinea 19 27 33 3.8

S. Guinea 46 51 50 10.0

Macronutrient loss versus consumption in Africa

4.4

0.5

3.0

0.8

0.3 0.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

N P KNutrients

Mill

ion

ton

s p

er y

ear

LossConsumption

Biophysical and economic parameters related to household resource endowment

(Shepherd & Soule, 1998)

Indicator Units Farm resource endowment Low Medium High Soil C balance kg ha-1 yr-1 –400 –318 190 Soil erosion t ha-1 yr-1 5.6 5.5 2.1 Farm returns $ yr-1 3 70 545 Household income$ yr-1 454 1,036 3,127

Effect of depth of soil mechanical de-surfacing at Mbissiri, Cameroon

0

1

2

3

0 5 7.5 10 12.5 15

Scoured depth (cm)

Maiz

e y

ield

(t

ha-1

)

Influence of mulch cover on erosion

0

50

100

150

200

0% 20% 24% 35% 50% 100%

Mulch cover in 1989, 1990 and 1991

Cu

mu

late

d e

rosi

on

in 1

98

9,

90

, 9

1 (

t h

a-1

)

Influence of cumulated erosion for a three year banana mulch on grain yield of next maize crop

0

1

2

3

4

5

0 50 100 150Cumulated erosion in 1989, 1990, 1991 (t ha-1)

Ma

ize

yie

lds

in 1

99

2 (

t ha

-1) No input

Manure

Manure+NPK

Manure+NPK+dolomite

Variability of soil organic carbon content at agro-ecosystem and

farm level

0

20

40

60

80

100

120T

ota

l S

yste

m C

(t

ha-1

)

Sen

egal

Riv

er V

alle

y

Sah

elia

n S

hru

bb

y G

rass

lan

d

(Syl

vo-p

asto

ral

Zo

ne)

Sah

alia

n-S

ud

anes

e T

ran

siti

on

Dri

er S

ud

anes

e W

oo

dla

nd

(Old

Gro

un

dn

ut

Bas

in)

Wet

ter

Su

dan

ese

Wo

od

lan

d

(New

Gro

un

dn

ut

Bas

in)

Su

dan

ese-

Gu

inea

n

Tra

nsi

tio

n

(Cas

aman

ce)

fore

stcu

ltiva

ted

graz

edcu

ltiva

ted

degr

aded

graz

edpa

rkla

nd

culti

vate

d

fallo

w

woo

dlan

dgr

azed

culti

vate

dfo

rest

park

land

fallo

wcu

ltiva

ted

Vegetation and Land Use

16.5o N 13.1o N16.1o N 15.2o N 14.8o N 14.1o N

Source: Woomer 2003

Carbon stocks and other fertility indicators of granitic soils in different agro-ecological zones in West Africa

Source: Windmeijer and Adriesse 1993

6281.624.55.30-20Equatorial

2870.493.36.80-20

3921.3911.75.70-20Guinea

Total P

mg/kg

Total N

g/kg

OC

g/kg

pH

H2O

Depth

(cm)

AEZ

6281.624.55.30-20EquatorialForest

2870.493.36.80-20Sudan Savanna

3921.3911.75.70-20GuineaSavanna

Total P

mg/kg

Total N

g/kg

OC

g/kg

pH

H2O

Depth

(cm)

AEZ

Carbon stocks of different subsystems in a typical upland farm in the Sudan-savanna zone

4.0-2420-2200.9-1.811-226.7-8.3Homegarden

0.6-15-160.2-0.52-55.7-6.2Bush

field

4.0-1113-160.5-0.95-105.7-7.0Village

field

ExchangeableK (mmol /kg)

Available P

mg/kg

Total N

g/kg

OC

g/kg

pH

H2O

AEZ

Source: Prudencio et al

Use of organic resources within a farm for variousfarmer typologies

Correlation (r) between selected soil (0-20 cm) fertility parameters and average annual rainfall

** and *** indicate statistical significance at the 0.05 and 0.001 level, respectively.  Source: Manu et al., 1991

Soil organic carbon losses are more related to clay and slit contents than rainfall

Ca CEC Corg Total N Clay RainfallpH KCl 0.62***a 0.64*** 0.65*** 0.62*** -0.02 0.25**

Ca 0.98*** 0.88*** 0.92*** 0.36*** 0.31***CEC 0.86*** 0.91*** 0.40*** 0.36***Corg 0.97*** 0.46*** 0.42***Total N 0.44*** 0.34***Clay 0.40***

Effect of soil and crop management on soil organic

carbon

Carbon losses (kg ha-1 yr-1) by erosion, runoff and leaching in the topsoil (30cm) in runoff plots

(Adopted from Roose E and Barthes B , 2001)

erosion runoff leaching

Adiopodoume (2100 mm rainfall)

Sub-equitoral forest 13 1 74 88

Cereals 1801 65 7 1873

Korogho (1300 mm rainfall)

Sudanian savanna 6 2 13 20

Maize, with fertilizers 65 18 3 84

Saria (800 mm rainfall)

Sudano-sahelian savanna 9 1 2 11

Cereals 150 5 0.3 115

C losses Totalstation

Annual loss rates of soil organic carbon measured at farm level in WASAT

Site Clay + silt (%)

Annual losses (K) (%)

Bambay 3 7

Saria (non eroded) 12 2

Saria eroded 19 6

silt + clay content (%)

0 20 40 60 80 100

g si

lt +

cla

y C

kg

-1 s

oil

0

20

40

60

80

2:1 clays

1:1 clays

Forest

Grassland

Cultivated

Source: Six et al., 2002

Relationship between silt+clay content and silt+clay associated carbon for different systems

Organic carbon changes under continuous cropping and under fallow in an ultisol

0

2

4

6

8

10

12

1 2 3 4 5 6 8 9 10

Year

Org

an

ic C

(g

/kg

)

Bare Fallow NPK+R NPK-R

Adapted from Kang 1993

Evolution of carbon content in the 0-10cm horizon, as affected by time and treatment in runoff plots of Mbissiri station,

Cameroon

0

2

4

6

8

1990 1991 1992 1993 1994

Ca

rbo

n c

on

ten

t (g

kg

-1)

Savanna Plowed, bare

Plowed, cropped Zero-tillage, cropped

0.10 0.20 0.30 0.40Organic Carbon (%)

0

20

40

60

80

So

il d

epth

(cm

)

Management

Control

Crop residue

Fertilizer

Crop residue & fertilizer

Fallow

Effect of different management on soil organic matter content,Sadore, Niger. Rainy season 1997

Se(±)=0.019

0.0 6.5 13.0400

600

800

1000

1200P

earl

mill

et g

rain

yie

ld (

kg.h

a-1)

M illet rotated with cowpea

Continous m illet

Effect of phosphorus and cropping system s on pearl m illet grain yields, Sadoré, Niger, rainy season 1992-1995.

S.E. = 38

Kg P/ha

Sorghum-groundnut rotation in Burkina Faso shows good crop as opposed to Continuous Sorghum crop (inset)

0 .0 6 .5 1 3 .0P h o sp h o ru s a p p lied (k g P /h a )

0 .2 0

0 .2 2

0 .2 4

0 .2 6

0 .2 8

0 .3 0S

oil o

rgan

ic c

arb

on (

%)

E ffect o f P h o sp h o ru s a n d cro p p in g sy stem o n so il o rg a n ic ca rb o n , S a d o re , N ig er , 1 9 9 5 .

C -M

M -M

M /C -C

M /C -M /C

S .E = 0 .02

Role of organic amendments on land productivity

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3Soil Organic C (%)

Mai

ze g

rain

yie

ld (

t/h

a)

Long distance

Compoundfields

Carsky et al., 1998

Phosphorus use efficiency (kg grain/kg P) in village (non degraded) and bush (degraded) fields for

pearl millet production, Niger

Nutrient Years Degraded Non degraded

2000 42 79

2001 47 79

P applied(26 kg P/ha)

0

500

1000

1500

2000

2500

3000

1960 1970 1980 1990

Grain

yie

ld (

kg

/ha)

Control

Fert + Manure

Fertilizer

Sorghum grain yield as affected by mineral and organic fertilizers over time.

Effect of cattle dung and urine on millet grain and total above ground bio-mass, Sadore Niger

Manure Dung + Urine - Urine

Application Grain Biomass Grain Biomass

Kg/ha

Cattle 0 - - 80 940

2990 580 4170 320 2170

6080 1150 7030 470 3850

7360 1710 9290 560 3770

s.e.m 175 812 109 496

Adapted from Powell et al., 1998

Effect of fertilizer application and crop residue on maize grain yield

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10

Year

Ma

ize

yie

ld (

t/h

a)

NPK+CR NPK-CR

CR-NPK Control

Yield after 10yrs, plot burnt Yield after 10yrs, plotmulched

Adapted from Kang 1993

Pearl millet total dry matter yield as affected by long-term application of crop residue and fertilizer

1983 1985 1987 1989 1991 1993 1995 1997Years

0

2000

4000

6000

8000

10000M

ille

t to

tal d

ry m

att

er

yie

ld (

kg h

a-1

)

C ontro l

C rop R esidue (C R )

Fertilizer (F )

C R + F

s.e. = 307

Source: Bationo et al, 1998.

Incremental millet grain and stover yield due to fertilization in sadore, Niger

Source: Bationo et al., 1995

Grain Stover

1985 CR - -Fertiliser 67 188CR + Fertiliser 137 427

1986 CR - -Fertiliser 57 184CR + Fertiliser 112 359

Year Treatment Fertiliser effect

----- kg per kg P applied ----

ORGANIC INPUTS FOR N MANAGEMENT Decision Guide

%N > 2.5

Yes

No

Lignin < 15% Polyphenols < 4%

Lignin < 15%

Yes

No

Yes

No

Incorporate directly

Mix with N fertilizer orhigh quality organic matter

Mix with N fertilizeror add to compost

Apply at the soil surface

y = 65.345x - 148.75

R2 = 0.6486

y = 25.721x - 74.13

R2 = 0.7362

-100

-50

0

50

100

150

0.00 1.00 2.00 3.00 4.00 5.00

N content (%)

% F

erti

lize

r eq

uiv

alen

t

Plant materials, low PP, W Africa

Plant materials, low PP, E+S Africa

Plant materials, high PP, W Africa

Calliandra, high PP, E+S Africa

FEs for Different Organic Materials

300

200

100

0

MICROBIAL CPARTICULATE CMINERAL-ASSOCIATED C

Fertilizer + + 0 0 + 0 +Stover 0 + + 0 0 + +Manure 0 0 0 + + + +

TYPE OF INPUT AFFECTS SOM COMPOSITION

(Kapkiyai et al., 1996)

IMP

RO

VE

ME

NT

IN

SO

IL C

(K

G/H

A/Y

R)

Base saturation and pH (water) for soil experiments in Saria, Burkina Faso

Treatment Base saturation

pH

Control 0.63 5.2

Chemical fertilizer 0.37 4.6

Crop residues 5t ha-1 0.7 5.2

(Source: Pichot et al 1981)

Soil pH as affected by soil depth and management practices. Sadoré, Niger, rainy season, 1996

3.9 4.1 4.3 4.5 4.7 4.9

pH (K C l)

0.0

0.2

0.4

0.6

0.8

So

il d

ep

th (

m)

s.e. = 0.06

C ontro l

C rop residue (C R )

Fertilizer (F )

C R + F

Fallow

Maximum phosphorus sorbed as affected by soil depth and management practices, Sadoré, Niger, 1999

30 50 70 90 110 130 150

M axim um P sorbed (m g P kg -1)

0.0

0.1

0.1

0.2

0.2

0.3

0.3

So

il d

ep

th (

m)

Contro l

C rop residue (CR)

Fertilizer (F)

CR + F

Availability of crop residue

• Optimum rate : 2 t ha-1

• Farmers field : 200kg ha-1

Farmers’ doses combined with the use of

small quantities of P fertilizers can boost

crop biomass.

Limitations

Utilisation de micro-dose de P (4kg/ha)

- P

+ P

Limitations

– Manure use is part of internal flow and does not add always nutrients from outside the farm

– Limited quantities, low nutrient content and often high labor demands for processing and application

– Potential livestock transfer of nutrients in W. Africa is 2.5 kg N and 0.6 kg P per hectare of cropland

– 5-20 tons recommended but less than 700kg is available in semi-arid W. Africa

– Can only increase yield by 2% per year

– Need between 10-40 ha of grazing land to maintain yield on 1 ha of cropland

Limitations

Future research challenge with emphasis on organic matter

quantity and quality

Future research challenges • Focus more on whether the organic resource quality concept is

also useful for predicting different degrees of stabilization of applied organic C in one or more of the organic matter pools

• Increasing the dual purpose grain legume component for improvement of soil organic carbon and for a better integration of crop-livestock production systems

• Improvement of nutrient use efficiency in order to offer cost- effective mineral fertilizer recommendations to the small-scale farmers

• Use of decision support systems, modelling, and GIS for the extrapolation of research findings