Soil organic carbon dynamics, functions and management in West African agroecosystems

1
Soil organic carbon dynamics, functions and
management in West African agro-ecosystems

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

2
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

3
The Vicious and Virtuous cycle
4
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
5
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

6
Introduction

• 16 of Africas 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

7
Increase in yield has been more due to land
expansion than to crop improvement potential
Based on three-year average for 1988-1990 and
1998-2000. FAO database.
8
Growth rate of millet 1979-1994
9
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
10
Macronutrient loss versus consumption in Africa
11
Biophysical and economic parameters related to
household resource endowment
(Shepherd Soule, 1998)
12
Effect of depth of soil mechanical de-surfacing
at Mbissiri, Cameroon
13
Influence of mulch cover on erosion
14
Influence of cumulated erosion for a three year
banana mulch on grain yield of next maize crop
15
Variability of soil organic carbon content at
agro-ecosystem and farm level
16
(No Transcript)
17
Carbon stocks and other fertility indicators of
granitic soils in different agro-ecological zones
in West Africa
Source
Windmeijer
and
Adriesse
1993
18
Carbon stocks of different subsystems in a
typical upland farm in the Sudan-savanna zone
Source Prudencio et al
19
Use of organic resources within a farm for
various farmer typologies
20
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
21
Effect of soil and crop management on soil
organic carbon
22
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)
23
Annual loss rates of soil organic carbon measured
at farm level in WASAT
24
Relationship between siltclay content and
siltclay associated carbon for different systems
Forest
21 clays
Grassland
11 clays
Cultivated
Source Six et al., 2002
25
Organic carbon changes under continuous cropping
and under fallow in an ultisol
Adapted from Kang 1993
26
Evolution of carbon content in the 0-10cm
horizon, as affected by time and treatment in
runoff plots of Mbissiri station, Cameroon
27
(No Transcript)
28
Kg P/ha
29
Sorghum-groundnut rotation in Burkina Faso shows
good crop as opposed to Continuous Sorghum crop
(inset)
30
(No Transcript)
31
Role of organic amendments on land productivity
32
(No Transcript)
33
Phosphorus use efficiency (kg grain/kg P) in
village (non degraded) and bush (degraded) fields
for pearl millet production, Niger
34
(No Transcript)
35
Effect of cattle dung and urine on millet grain
and total above ground bio-mass, Sadore Niger
Adapted from Powell et al., 1998
36
Effect of fertilizer application and crop residue
on maize grain yield
Adapted from Kang 1993
37
Pearl millet total dry matter yield as affected
by long-term application of crop residue and
fertilizer
Source Bationo et al, 1998.
38
Incremental millet grain and stover yield due to
fertilization in sadore, Niger
Year
Treatment
Fertiliser effect
Grain
Stover
----- kg per kg P applied ----
1985
CR
-
-
Fertiliser
67
188
CR Fertiliser
137
427
1986
CR
-
-
Fertiliser
57
184
CR Fertiliser
112
359
Source Bationo et al., 1995
39
ORGANIC INPUTS FOR N MANAGEMENT Decision Guide
40
FEs for Different Organic Materials
41
(No Transcript)
42
Base saturation and pH (water) for soil
experiments in Saria, Burkina Faso
(Source Pichot et al 1981)
43
Soil pH as affected by soil depth and management
practices. Sadoré, Niger, rainy season, 1996
44
Maximum phosphorus sorbed as affected by soil
depth and management practices, Sadoré, Niger,
1999
45
Availability of crop residue
Limitations

• 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.

46
Utilisation de micro-dose de P (4kg/ha)
P
- P
47
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

48
Limitations

• 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

49
Future research challenge with emphasis on
organic matter quantity and quality
50
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

51
Je vous remercie