Material and Methods
Thesis Report Soil Formation and Ecopedology (SFI-80826)
Organic matter stocks under different types of land use
in the Peanut Basin of the Nioro area, Senegal.
Author: Abibou Niang
September 2004
Supervisors: Dr. Jetse Stoorvogel, Dr. Marcel Hoosbeek, Dr. Bocar Diagana
Examiner:
Prof. Dr. Nico van Breemen
DEPARTMENT OF ENVIRONMENTAL SCIENCES
LABORATORY OF SOIL SCIENCE AND GEOLOGY
12
Material and methods
Organic matter stocks under different types of land use
in the Peanut Basin of the Nioro area, Senegal.
Abibou Niang
Thesis submitted in the partial fulfillment of the degree of Master of
Science in Soil Science at Wageningen University and Research
Center.
Supervisors: Dr. Jetse Stoorvogel, Dr. Marcel Hoosbeek, Dr. Bocar Diagana
Examiner: Prof. Dr. Nico van Breemen
September 2004
Wageningen University
Laboratory of Soil Science and Geology
TABLE OF CONTENTS
13
Material and methods
TABLE OF CONTENTS……………………………………………………………...…i
LIST OF TABLES………………………………………………………………………iii
LIST OF FIGURES………………………………………………………………..……iv
LIST OF PICTURES……………………………………………………………………v
ABBREVIATIONS AND SIGLES…………………………………………………….vi
PREFACE……………………………………………………………...……………….vii
ACKNOWLEDGEMENT…………………………………...………...………………viii
DEDICATION……………………………………………...……………………………ix
I. INTRODUCTION .................................................................................................................................. 1
1.1 PROBLEM DEFINITION ................................................................................................................... 1
1.2 ORGANIC MATTER POOLS IN SOILS ........................................................................................... 3
1.3. DESCRIPTION OF THE AREA........................................................................................................ 5
1.3.1. LOCATION AND CLIMATE .......................................................................................................... 5
1.3.2 SOILS AND VEGETATION ............................................................................................................ 8
1.3.3. LAND USE AND LAND MANAGEMENT ..................................................................................... 9
II MATERIAL AND METHODS ............................................................................................................. 13
2.1 SOIL SAMPLING ............................................................................................................................ 13
2.2 SOIL PREPARATION AND SOIL ANALYSIS ............................................................................... 14
2.3 LAND MANAGEMENT SURVEY .................................................................................................... 15
2.4 DATA ANALYSIS............................................................................................................................ 15
III RESULTS AND DISCUSSIONS ....................................................................................................... 16
3.1 SOIL DESCRIPTIONS .................................................................................................................... 16
3.2 LAND USE DESCRIPTIONS .......................................................................................................... 16
3.3 CARBON STOCKS ......................................................................................................................... 17
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Material and methods
3.3.1 CARBON DISTRIBUTION AND PH ALONG THE LANDSCAPE .............................................. 17
3.3.2 DISTRIBUTION OF ORGANIC CARBON IN DIFFERENT LAND USE ...................................... 19
3.4 RELATIONSHIP BETWEEN TOTAL CARBON AND OTHER SOIL PROPERTIES .................... 22
3.4.1 CARBON AND NITROGEN ......................................................................................................... 22
3.4.2 CARBON AND PH ....................................................................................................................... 22
3.4.3 CARBON AND TOTAL FINE FRACTIONS ................................................................................. 23
3.4.4 CARBON AND BULK DENSITY ................................................................................................. 23
3.4.5 TOTAL ORGANIC CARBON, RECALCITRANT CARBON AND NITROGEN........................... 23
3.5 POTENTIAL FOR CARBON SEQUESTRATION ........................................................................... 26
IV CONCLUSION .................................................................................................................................. 28
REFERENCES ...................................................................................................................................... 29
ANNEXES ............................................................................................................................................. 32
SOIL DATA ........................................................................................................................................... 33
LAND OBSERVATION AND LAND MANAGEMENT SURVEY .......................................................... 37
GRAPHS ............................................................................................................................................... 78
METEOROLOGICAL DATA ................................................................................................................. 84
PICTURES ............................................................................................................................................. 87
List of tables
pages
Table 1: Identification of different types of land use in the Nioro area………………………………….17
Table 2: Soil properties along the landscape in the upper 20 cm………………………………………...19
Table 3: Carbon distribution (%) in three different landscapes in the upper 20 cm ……………..............19
Table 4: Distribution of carbon under different types of land use…………………………………..……20
Table 5: Average carbon content in the upper 20 cm in different types of land use ranked according to their
carbon input……………………………………………………………………..…………………….......20
Table 6: Total carbon and total nitrogen in different types of land use……………..……………………22
Table 7: Land use and carbon and nitrogen recalcitrance on the topsoil (upper 10cm)……….………….24
Table 8: Land use and carbon and nitrogen recalcitrance in the subsoil (20 cm depth)………….……….24
15
Material and methods
Table 9: Land use and carbon and nitrogen recalcitrance in the bas fond subsoil……………….………..24
Table 10: Carbon and nitrogen recalcitrance in the whole profile of a bas fond (100 cm depth)………....25
Table 11: Carbon stocks in the upper 20 cm in t ha-1 in different positions of the landscape……….…….26
Table 12: Carbon stocks in the upper 20 cm in t ha-1 in different types of land use………………………26
Table 13: Djiguimar data set……………………………………………………………………………….34
Table 14: Paoskoto data set………………………………………………………………………………...35
Table 15: Porokhane data set………………………………………………………………………….........36
Table 16: Rainfall data in the Nioro area from 1950 to 2001………………………………………………85
Table 17: Mean annual maximum and mean annual minimum temperature in the Nioro area………..….86
16
Material and methods
List of figures
pages
Figure 1: Partial expanded view of belowground carbon cycling, recycling and dissipation as CO2..........5
Figure 2: Senegal localization in Africa……………………………………………………………………6
Figure 3: Overview of the study area……………………………………………………………….……....6
Figure 4 : Rainfall variation from 1950 to 2001……………………………………………………………7
Figure 5: Maximum and mean temperature in Nioro area from 1985 to 2000……………………………..7
Figure 6: Senegal simplified soil type’s representation……………………………………………………8
Figure 7: A typical topo-sequence in the Nioro area………………………………………………….…….9
Figure 8: Representation of the sampling pattern…………………………………………………….……13
Figure 9 : carbon content (%) in the upper 20 cm and carbon input…………………....................….……21
Figure 10: Relationship between total carbon and total nitrogen………………………….………….……22
Figure 11: Relationship between total carbon and recalcitrant carbon……………………….………….…24
Figure 12: Relationship between recalcitrant carbon and recalcitrant nitrogen……………………….……26
Figure 13: clay + silt, bulk density pH and carbon along the landscape (upper 20 cm)…………………...79
Figure 14: distribution of carbon in average along the landscape………………………………………….79
Figure 15: Carbon distribution in a short (602 m) sloping landscape (5 %)………………………………..79
Figure 16: carbon distribution in a long (1810 m) gentle slope (< 1%)……………………….……………80
Figure 17: carbon distribution in a short (685 m) gentle slope (< 1%)……………………………………..80
Figure 18: distribution of carbon in different types of land use…………………………………………….80
Figure 19: distribution of carbon in the bas fond profile in short sloping landscape………………………81
Figure 20: distribution of clay in the bas fond profile in short sloping landscape…………………………81
Figure 21: distribution of sand in the bas fond profile in short sloping landscape…………………….…...81
Figure 22: distribution of carbon in the bas fond profile in short and long gentle slope landscape…….….82
Figure 23: distribution of clay in the bas fond profile in short and long gentle slope landscape……….….82
Figure 24: distribution of sand in the bas fond profile in short and long gentle slope landscape………….82
Figure 25: distribution of sand in the bas fond profile in a long and a short gentle slope landscape……....83
List of pictures
pages
picture 1: soil and vegetation in the plateau…………………………………………………88
picture 2: plateau soil profile………………………………………………………………...88
17
Material and methods
picture 3: rock stone in the plateau subsoil…………………………………………………..88
picture 4: glacis soil profile………………………………………………………………….88
picture 5: terrace soil profile…………………………………………………………………88
picture 6: bas fond soil profile……………………………………………………………….88
picture 7: sand deposition in the bas fond sub soil…………………………………………..88
picture 8: sand deposition in the bas fond top soil…………………………………………...88
picture 9: cattle feeding with crop residues in dry season……………………………………88
picture 10: soil sample taking using auger…………………………………………………...88
picture 11: steps for bulk density measurement………………………………………...........89
picture 12: Steps for composite samples making…………………………………………….90
picture 13: pH measurement………………………………………………………………….90
picture 14: texture measurement by pipette method………………………………………….90
picture 15: carbon determination by Walkley and Black……………………………………..90
18
Material and methods
ABBREVIATIONS AND SIGLES
TOA: Trade-Off Analysis
ISRA: Institut Sénégalais de Recherches Agricoles
SM-CRSP: Soil Management – Collaborative Research Support Program
USAID: United States of America Aid for International Development
OM: Organic Matter
SOM: Soil Organic Matter
BD: Bulk Density
TOC: Total Organic Carbon
Rec: Recalcitrant
FAO: Food and Agriculture Organization
GPS: Geographical Position System
CRCPLI: Continuous Rotation Cereal Peanut without or Low external Input
CRCPHI: Continuous Rotation Cereal Peanut with High external Input
PFP: Permanent Fallow in the Plateau
PFT: Permanent Fallow in the Terrace
PFBF: Permanent Fallow in the Bas Fond
CCBF: Continuous Cereal Cultivation in the Bas Fond
CCP: Continuous Cereal cultivation under Parkland.
19
Material and methods
Preface
This work is an Msc thesis in soil science in the University of Wageningen. Thesis research
was done in the ISRA (Senegalese Institute of Agricultural Research) station of Nioro in
Senegal in the context of the Trade-Off Analysis project (TOA). The TOA project in West
Africa is a collaborative Carbon sequestration project between Montana State University,
Wageningen University and four West African countries (Senegal, Ghana, Mali and Togo). In
Senegal the project is collaborating with ISRA, and other relevant projects and institutions.
The aim of the project is to analyze the technical and economic potential for adoption of
technologies and practices that enhance carbon sequestration and the sustainability of
agricultural production systems. In addition, the TOA team is developing collaborations with
institutions in Ghana and Mali in conjunction with the SM-CRSP (Soil Management –
Collaborative Research Support Program) Carbon Project. More information is available at
the project’s website: http://www.tradeoffs.nl or http://www.tradeoffs.montana.edu.
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Material and methods
Acknowledgement
The work reported here was conducted with the collaboration of the trade off analysis project
of the USAID SM-CRSP program in Senegal and the Senegalese Institute for Agricultural
Research. Without their help this work will never be completed. I take this opportunity to
express my thanks to all of them.
My thanks go to the General Director of ISRA for allowing me a scholarship and giving me
the opportunity to complete my study in Wageningen University. Thanks are due to the
Scientific Director of ISRA, Dr Taib Diouf and to Dr Ali Ndiaye head of the training
program.
I’m indebted to my supervisors Dr. Jetse Stoorvogel and Marcel Hoosbeeck, who showed
confidence in my work during my field period in Senegal. They gave lots of constructive
criticism, which helped me a lot in writing down this report. Many thanks to Dr Jetse
Stoorvogel for allowing me a month of living allowance to complete this thesis report.
I want to thank Eef Velthorst of the laboratory of soil science and geology for his assistance
and help in laboratory matters.
Thanks and gratitude beyond measure go to Dr Mamadou Khouma Dr Modou Sene, and Dr
Bocar Diagana, my supervisors in Senegal, for their guidance and assistance during my
fieldwork. Special thanks are due to Dr Modou Sene and his technician Elhadji Moussa Diop
who provided me with all the equipment I needed for data collection and bulk density
measurement. I extend thanks to André Mankor with whom I shared office, to Merry Ndiaye
the secretary of the LNERPV, and to Cheikh Mbay, the car driver for his nice driving.
I want to give special thanks to Mbaye Diaw “my” field technician, he helped me a lot in the
field work and shared with me all the troubles with the high temperature in the area. Thanks
are also due to Macoumba Diop and his wife Cecile and all the staff of the Nioro station.
A lot of thanks are due to all the peasants of the villages of Djiguimar, Paoskoto and Prokhane
for their collaboration in this study and special thanks to Mor Coumba Toure, my host family
in Djiguimar.
I’m much thankful to Dr Alioune Fall head of ISRA St Louis, Dr Moustapha Dieye head of
soil laboratory and my brother Babacar Ngom, for their help and invaluable assistance and
through them I want to thank all the staff of ISRA St Louis.
I express here all my thanks and gratitude to my parents for their efforts to give me education,
to my brothers and sisters and to all my friends. I will never forget my brother Moussa Ndoye,
a qui je dis Merci du fond du cœur.
I want to thank Simone Radersma , Nico and Rijke van Breemen for helping me to forget the
long distance from home.
And finally to my wife and my daughter, Mounass and Aicha, love and affection beyond
words.
And last but not least to God for giving me faith and strength to live for a so long time so far
from home.
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Material and methods
This thesis is dedicated to the memory of the late Dr Mabeye Sylla, soil scientist in ISRA; he
has got his PHD degree in 1994 in Wageningen University. He made me fall in love with
soil science and provided me with long –lasting fun and flavor for the profession of soil
scientist. Very early, in August 1995,
he was taken out from our affection…We will never forget…
I. INTRODUCTION
1.1 Problem definition
Soil degradation has become a major concern in sub-Saharan Africa (Oldeman et al. 1990).
Erosion, salinization, acidification and the loss of organic matter are the main forms of soil
degradation. The loss of soil organic matter (SOM) is a slow process that is related to
improper management practices and natural degradation processes. In low-input farming
systems in sub-Saharan Africa, organic matter is an important production factor (Manlay et al,
2002). Organic matter plays a major role in the productivity of soils and is particularly
important in terms of soil fertility and the water holding capacity of strongly weathered soils
of the tropics (Coleman et al, 1989). Additionally, SOM binds soil particles together to form
stable aggregates that are resistant to erosion, and at the same time, permit water to infiltrate
easily, thereby reducing runoff. In adequate quantities, SOM reduces soil crusting and soil
bulk density, and helps to maintain a stable soil pH. As SOM content increases, soil nutrients
such as available nitrogen, phosphorus and sulfur increase as well; trace elements like zinc,
iron, copper, manganese also increase. As a result, SOM improves soil tilth, and helps to
provide a favorable medium for crop growth.
Soil organic matter is a dynamic soil property. Inputs to soil occur from above as leaf litter,
woody litter, insect and animal debris, and dissolved organic C from canopy drip. Assimilated
C is moved belowground in root systems, including exudates, and by soil fauna. Some organic
materials are utilized and turn over quickly (labile pools), but some remain in the soil for long
periods of time (stable pools). Turnover is affected by interactions involving inorganic soil
components, by location of organic matter in zones inaccessible to microorganisms and their
22
Material and methods
enzymes (Coleman et al, 1989) and by climate factors (temperature, moisture). Annual
additions of C to most soils are matched by losses due to respiration and leaching and a steady
state exists so that the content of SOM remains constant. Turnover times of SOM in tropical
soils are much shorter than in temperate soils (Coleman et al, 1989), decreasing the steady Ccontent of soils. Various management practices may further disturb the steady state C of soils.
Practices that increase the net primary production or the amount of plant material allocated
into litter have the potential to increase soil carbon stocks. Batjes (2000) stated that the
agricultural management practices recommended to build up carbon stocks in the soil are
basically those that increase the input of organic matter to the soil and/or decrease the rates of
soil organic matter decomposition. These practices will generally include a combination of the
followings: tillage methods and crop residue management - soil fertility and nutrient
management - erosion control - water management - crop selection and rotation.
The degradation of SOM results in the emission of carbon dioxide from the system. Carbon
dioxide absorbs heat and thus contributes to the greenhouse effect. The potential ramification
of elevated carbon dioxide on climate change makes it necessary to reduce carbon dioxide
emissions. The buildup of carbon dioxide in the atmosphere is increasing by more than 3
billion tons per year. Sokona (1995) cited by Manlay et al (2002) reported that in Senegal,
more than 40 % of carbon dioxide emissions come from agriculture, land use changes and
forest.
Thus, there is an increasing need to reduce the degradation of SOM or even sequester more
carbon in agricultural soils. Significant potential for carbon sequestration can be expected in
general with changes to agricultural management practices such as no-till cropping, pasturecrop rotations and better grazing management (Hill, 2003). The estimated amount of carbon
stored in world soils is about 1100 to 1600 petagrams, more than twice the carbon in living
vegetation (560 petagrams) or in the atmosphere (750 petagrams). Hence, even relatively
small changes in soil carbon storage per unit area have a significant effect on the global
carbon balance.
Carbon sequestration in soils occurs through plant production or organic manure. Plants
convert carbon dioxide into tissue through photosynthesis. After the plant dies, plant material
is decomposed, primarily by microorganisms, and much of the carbon in the plant material is
eventually released through respiration back to the atmosphere as carbon dioxide. But some of
it remains when organic material decays and leaves behind organic residues called humus.
These residues can persist in soils for hundred or even thousands of years. Many factors can
slow the decay of organic materials and, as a result, affect a soil’s capacity for storing carbon.
Inherent factors include climate variables (temperature and rainfall), clay content and
mineralogy. While SOM additions have been discussed in terms of dry matter inputs, SOM
losses fall under two major categories: losses from erosion and from decomposition. Erosion
represents the physical loss of SOM when clay and silt are removed from the field by wind
and water. Decomposition is a chemical loss of SOM as carbon dioxide when microbes use
23
Material and methods
SOM as food for energy and growth. Since SOM is becoming increasingly scarce in West
African soils, there is a need to assess organic matter allocation in local ecosystems related to
land management (Manlay et al, 2002). In the context of the Trade-Off Analysis (TOA)
project in Senegal, we aim to study the relationship between organic matter and agricultural
management practices in the peanut basin at Nioro in Senegal.
The objective of this study is to contribute in the understanding of the effect of agricultural
land management on organic matter stocks and more specifically on the potential for carbon
sequestration in the area. Stocks of carbon and recalcitrant carbon pools are quantified for
different plots with differences in land use history.
1.2 Organic matter pools in soils
The quality of soil organic matter depends on its distribution among labile and recalcitrant
pools and the quality of each pool considered (Rovira et al, 2001). Batjes (2000) stated that
soil organic matter must be subdivided into several compartments considered more or less
‘homogeneous’ in terms of residence times Eswaran et al (1995) defined four pools based on
carbon dynamics. First, an ‘active or labile’ pool of readily oxidized compounds, the
formation of which is largely dictated by plant residue inputs and climate. Second a ‘slowly
oxidized pool’ associated with soil macro aggregates, the dynamics and pool size of which are
affected by soil physical properties such as mineralogy and aggregation, as well as agronomic
practices. Third, a ‘very slowly oxidized pool’ associated with micro aggregates, where the
main controlling factor is water stability of the aggregates and agronomic practices have only
little effect. Fourth, a ‘passive or recalcitrant pool’ where clay mineralogy is the main
controlling factor, and there are probably no effects due to agronomic practices. Duxbury et
al, (1989), cited by Gabrielle et al (2002) stated that the pools may be broken into three
categories:
microbial biomass, which comprises the living micro-organisms responsible for the
biological attack of the other forms of (dead) OM
2. labile, fresh OM derived from recent crop inputs (roots, root exudates, plant litter,
etc…), that are undergoing decomposition by the microbial biomass
3. Stabilized OM that decays more slowly because it is temporarily or permanently
inaccessible to the microbial biomass.
The three main pools of SOM are determined by their time for complete decomposition. They
are active (1-2 years), slow (15 – 100 years) and passive (500 – 5000 years) (Brady and Weil,
1999). Both active and slow SOM are biologically active, meaning they are continually being
decomposed by micro-organisms, releasing many organically bound nutrients, such as N, P,
and other essential nutrients back to the soil solution. Active SOM is primarily composed of
fresh plant and plant residues and will decompose fairly rapidly. Active SOM that is not
completely decomposed moves into slow or passive SOM pools. Slow SOM, consisting
primary of detritus (cells and tissue of decomposed material), is partially resistant to microbial
decomposition and will remain in the soil longer than active SOM. In contrast to active and
1.
24
Material and methods
slow SOM, passive SOM, or humus, is not biologically active and is the pool responsible for
many of the soil chemical and physical properties associated with SOM and soil quality.
Representing 35-50 % of total SOM, humus is a complex mixture of organic substances
modified from original organic tissue, synthesized by various soil organisms, and resistant to
further microbial decomposition (McCauley et al 2003) (figure 1) .
25
Material and methods
Figure 1: Partial expanded view of belowground carbon cycling, recycling and dissipation as CO2 (source from
McCauley et al, 2003).
1.3. Description of the area
1.3.1. Location and climate
The study was carried out between April and June 2003 in the peanut Basin of the Nioro area
in Senegal (figure 2). The landscape can be subdivided into two major physiographic units
with sloping and gently sloping areas respectively. The gentle slope (1 to 2%) may have a
length of several kilometers while the sloping areas (2 to 5%) are generally less than a
kilometer. The villages of Djiguimar, Paoskoto and Prokhane have been selected to describe
the distribution of organic matter in different land use systems: Djiguimar and Paoskoto for
their particular landscape and Prokhane for the high input intensified agriculture practiced
herein. Djiguimar (between 13º 36’ and 13º 40’ North and 15º 31’ and 15º 35’ West) is
situated 26 km south east of Nioro du Rip and was selected to study the organic matter
distribution in a sloping landscape. Paoskoto (between 13º 45’ and 13º 50’ North and 15º 45’
and 15º 49’ West) situated 5 km north of Nioro was selected to study the organic matter
distribution in gentle sloping landscapes. Prokhane (between 13º 40’ and 13º 42’ North and
15º 50’ and 15º 52’ West) at 8 km West from Nioro is one of the villages where high input
agriculture takes place and is practiced by the rich farmers belonging to the influent
“mouride” religious family. This village was selected to compare carbon stocks under low and
high input agricultural management on gentle slopes (figure 3).
26
Material and methods
Figure 2: Senegal localization in Africa
Kaolack
South
Paoskoto
Nioro
Prokhane
Djiguimar
Administrative cities
villages
national roads
Secondary roads
Sandy roads
Figure 3: Overview of the study area
The climate is classified as Sudanian. Over the last years the average annual rainfall ranged
between 700 to 800 mm. Rainfall is mono-modal and lasts for 5 months from June to October
(figure 4). The mean annual temperature is about 28 º C. The mean maximum and minimum
temperatures are respectively 38 º C and 15 º C (figure 5). The mean potential
evapotranspiration is 1800 mm yr-1 (Iyamuremye, 2000).
27
Material and methods
1400
1200
Rainfall in mm
1000
Jun
Jul
800
Aug
Sep
600
Oct
Tot
400
200
19
50
19
54
19
57
19
61
19
64
19
67
19
70
19
73
19
76
19
79
19
82
19
85
19
88
19
91
19
94
19
97
20
00
0
Years
Figure 4 : Rainfall variation from 1950 to 2001 (data : see annexes, source : Meteorological center of CNRA de
Bambey).
40
Mean Temp (Clecius)
35
30
25
Max mean temp
20
Min mean temp
15
10
5
2000
1999
1998
1997
1996
1994
1993
1992
1990
1989
1988
1986
1985
0
Years since 1985
Figure 5: Maximum and mean temperature in Nioro area from 1985 to 2000 (data : see annexes, source :
Meteorological center of CNRA de Bambey).
28
Material and methods
1.3.2 Soils and vegetation
Following FAO (1998), the soils are mainly classified as ferric lixisols on the plateau and
haplic lixisols in the glacis. In the bas fond with seasonal water flooding soils are mostly
classified as a haplic gleysol. In the French classification these soils are referred to the groups
“sols ferrugineux tropicaux lessivés”, “sols ferralitiques” and “sols hydromorphes” (Pieri,
1969, Khouma, 2000) (figure 6).
(
Figure 6: Senegal simplified soil type’s representation (Khouma, 2000)
The plateaus are generally populated with herbs and shrubs. Two shrub species dominate the
vegetation and account for 80 % of woody above-ground biomass: Guieria senegalensis and
Combretum glutinosum. Andropogon pseudapricus and Pennisetum pedicellatum are the most
dominant herbaceous plant.
The glacis, mostly cropped, is covered with food crops and it is common to find the same
shrub and herb species as on the plateaus. A few numbers of trees like acacia albida and
Cordyla pinnata are also found in this part of the landscape.
29
Material and methods
Annual water flooding in the Bas fond may explain the good chemical status and better
physical conditions of the soils in that area. In the dry season, soils are well covered and more
species of trees, shrubs and herbs are found in this unit. In addition to the vegetation found on
the plateau we can find other species like Spermaceae achydea, Eragrostis tremula, Vitex
doniana, Mitracrapus scaber, for the herbaceous plants ; Prosopis africana, Hibiscus asper,
Piliostigma reticulatum, Combretum lecardii, Terminalia macroptera, Calotropis procera,
Strychnos spinosa, Acacia macrostachya, Securidaca longipedonculata, Cassia siberiana for
shrub population and Ziziphus mauritiana Azadirachta indica, Acacia seyal, Bombax
costatum for the tree species population (figure 7).
Soils
ferric lixisol
-------------------- ---------------------------------------------
Land use
permanent fallow
-------------- ---------------------------------------------
haplic lixisol
------------------------------------------------------
haplic gleysol
-------------------------------------------
cereal / peanut
-----------------------------------------------
continuous cereal
-------------------------------
Figure 7: A typical topo-sequence in the Nioro area (Picture from Manlay et al, 2002).
1.3.3. Land use and land management
a) Land use
Agriculture in the area is essentially based on intense cultivation (pressure on the land)
without mineral fertilizer or organic matter input. The cultivation is mainly rain-fed,
traditional and non-mechanized.
The glacis which is the sloping part situated between the plateau (high land) and the bas fond
(lowland) are mostly used for agriculture. Peanut (Arachis hypogaea L.) and millet
(Pennisetum glaucum L.) are the principal crops cultivated since a long time in the area.
Recently, this trend has been disrupted because of crop seeds shortage. In 2003 maize (Zea
mays L.) has been largely cultivated in the area as a result of a government program. Sesame
has been introduced recently into the area and is increasingly being cropped by farmers.
Sorghum (Sorghum bicolor L.) is another important crop cultivated which together with millet
and maize are the main subsistence crops or food crops. In the past, rice was one of the main
crops cultivated in the flooded bas fond, but according to peasants this is not practiced
anymore for technical reasons.
30
Material and methods
The plateaus with iron-stones are mostly uncultivated (picture 1); they are the only place
where permanent fallow can be found and are the only green part just after harvest. During the
dry season the fields where peanut have been cultivated are easily recognizable because no
crop residues are left behind to cover the land. As peanut crop residues are as valuable in the
market (as animal fodder) as the crop itself, everything is removed at harvest leaving the land
uncovered and the topsoil left to the wind (erosion) and water (runoff) for transportation to the
lower area..
From the other fields cultivated with the subsistence crops (millet, maize and sorghum), crop
residues are also removed but only the strongest stalks are taken away to build house fences
building and most of the straw is left behind, and is fodder for cattle. Consumption of crop
residues and the herbaceous biomass of fallows by cows is accompanied by irregular
manuring of the fields during browsing throughout the dry season (Manlay et al, 2002). In
addition, plant residues, on the top surface may help reduce wind erosion.
b) Land management
Removal or burning of crop residues predisposes the soil to serious erosion. Unfortunately in
the whole area the remaining crop residues are burnt in situ just before the start of the rainy
season when preparing seedbed for the next crop. For the peasants, burning is an inexpensive,
labor efficient means of removing unwanted crop residues prior to tillage or seedbed
preparation. Burning is mostly done not just simply to remove straw but also to reduce
diseases where it’s believed that straw serves as a pathogen host. According to some of the
landowners burning can also control weeds and insects to some extent, that’s why even in the
uncultivated rocky plateaus periodical fire may occur as the result of burning.
However, burning can have some detrimental effects. Crop residues consist of about 50
percent carbon, and carbon is volatile under most fire conditions, causing the loss of carbon to
the air. Nearly all of the nitrogen and about half of the sulfur and phosphorus are also lost
(USDA, 2004). Some of these effects are - removal of the extra vegetative material that
would add humus and nitrogen into the soil, - destruction of old vegetation in the soil which
acts to increase water holding capacity. A number of soil properties besides organic matter
level can be permanently affected by long term burning of crop residues. Some of the
detrimental effects of long term burning include decreases in organic matter, total nitrogen,
total sulfur, carbon/nitrogen ratios, extractable carbon, polysaccharide, ammonium, and
available phosphorus.
We learned, from talking to many farmers that plowing crop residues practices was introduced
to them in the early 1980s or even earlier by agriculture-based non government organizations
and some agricultural officers who had foresight and believed in the benefits of using crop
residues to fertilize the soil. Some of these farmers practiced it as long as those organizations
were around. As soon as they left, they gave up and went back to their old practices.
31
Material and methods
II Material and methods
2.1 Soil Sampling
The topo-sequences sampled ranged from the high land (plateau) to the low land (bas fond)
(figure 7). To assess the distribution of carbon through the landscape, three parallel transects
have been made in a short (602 m) sloping area (5 %) situated in the village of Djiguimar, one
transect in a long (1810 m) gentle slope (< 1%) area and one transect in a short (685 m )
gentle sloping area both in the village of Paoskoto. In Prokhane where land management was
the subject of study, two transects have been made, taking into account the two different types
of management, low input and high input cultivation. Neighboring crop fields, fallow plots
and parklands of different ages were considered as representative of the same plot, assuming
they shared the same initial soil properties and management history (Manlay et al 2002).
Soil sampling has been done along the 5 transects. Every individual field crossed by a transect
is considered as a different land use pattern and is a sampling point. The transects consisted of
16 sampling points in Djiguimar, 16 sampling points in Paoskoto and 8 sampling points in
Prokhane. The field is first explored and a representative area of the land was chosen. By
personal feeling the selected area is as similar as the majority of the piece of land in terms of
soil physical properties and nutrient status. Geographical coordinates of these points were
recorded using GPS. Four different samples were taken per field at two depths (10 and 20
cm), using an auger and mixed to form a composite sample. The sampling points were 2
meters distant from the bulk density measurement point and 4 meters from each other (figure
8). For bulk density measurements, the dry soil was first moistened using water to facilitate
the cylinder penetration into the soil. Then the cylinder was hammered into the soil and dug
out (pictures 11 in annexes). The soil was trimmed to the size of the cylinder, removed from
the cylinder and collected in a pre-weighed pot for further oven drying and weighing.
Knowing the weight of the soil and the dimensions of the cylinder, the bulk density of the soil
can be obtained. This has been done in horizontal planes at 10 cm and 20 cm depth.
32
2m
2m
Bulk density
measurement
point
Sampling
points
Figure 8: Representation of the sampling pattern.
In the bas fond where soils are deeper, samples were taken at 10, 20, 30 and 40 cm depth.
For one sampling point where the top 40 cm was very sandy, samples were taken until 1
meter depth (10, 20, 30, 40, 50, 60, 90, 100 cm).
The color of the soil has been described for each depth using the Munsell color chart
book. The different types of vegetation (tree, shrubs and herbs), the existence of roots and
the biological activity have been recorded for each field sampled. The table below has
been filled out for each sampling point.
i
Observation
Village:
Transect number:
Parcel number:
GPS Coordinates:
Position on the landscape:
Vegetation types:
Landowner:
Depth (cm)
Color
Texture
Roots
Biological
Activity
Other observ
10
20
30
40
2.2 Soil preparation and soil analysis
Soils have been already air dried while sampling. The temperature in the area was
between 45 and 49 degrees Celsius. The soil samples were grind and passed through a 2
mm sieve prior to analysis.
Soil analysis has been carried out in the soil laboratory of ISRA Saint Louis in Senegal.
The pH has been measured in a suspension of water (Houba et al, 1989). Soils were
analyzed for sand, silt, and clay contents by pipette analysis following dispersion by
sodium hexametaphosphate (Olivier, 1978). Carbon content was estimated using wet
combustion of the Walkley and Black method (Houba et al, 1989). A representative set of
samples representing each type of landscape and each type of land use was selected for
pools of organic matter determination. The pools of organic matter are extracted using
acid hydrolysis. The labile and the intermediate pools were hydrolyzed using respectively
20 ml of 5 N H2SO4 and 2 ml of 26 N H2SO4, the remaining considered as the non
hydrolysable fraction was considered as the recalcitrant fraction (Rovira et al, 2002).
Total carbon and total nitrogen were determined in the original sample and in the
recalcitrant pool using dry combustion of the elemental analysis. The sample under test is
weighed in using a tin capsule. The required amount is 2 to 3 mg of organic material and
can hardly exceed 10 mg. After folding the capsule the sample is placed in the auto
sampler. The tin capsule enclosing the sample falls into the reactor chamber where excess
oxygen is introduced before. At about 990 °C the material is "mineralized". The complete
oxidation is reached at a tungsten trioxide catalyst which is passed by the gaseous
ii
reaction products. The resulting mixture should thus consist of CO2, H2O und NOx. But
also some excess O2 passes the catalyst. High purity helium is used as carrier gas. Finally
the gas mixture is brought to a defined pressure/volume state and is passed to a gas
chromatographic system. Separation of the species is done by chromatography. In this
technique a staircase type signal is registrated. Step height is proportional to the
substance amount in the mixture. Blank values are taken from empty tin capsules.
Calibration is done by elemental analysis of standard substances supplied by the
instrument's manufacturer for this purpose.
2.3 Land management survey
For each field sampled the landowner is recorded and questions about land management
and land history are asked using a formal questionnaire. The questionnaire is shown
below.
Land management:
Year of clearing:
Actual crop
Previous
2 years
3
4
5
6
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
2.4 Data analysis
Average values, maximum, minimum and standard deviation have been calculated using
Excel pivoting table. To study the relationships between carbon and soil properties in the
whole data set regression analysis has been performed. Types of land use have been
ranked using estimates of carbon input to each of them. A score was allocated to each
land use according to carbon input and relationship between land use and carbon content
has been studied with a regression analysis. All these statistical analysis have been
carried out using SPSS 12th version.
iii
III Results and discussions
3.1 Soil descriptions
Soils are generally very shallow in the plateaus and in the glacis (pictures 2 and 4,
annexes); they are respectively 30 cm and 40 cm deep. In the terraces and in the bas fond
soils are mostly deep; they are 60 to 70 cm deep in the terraces and more than 150 cm
deep in the bas fond ( picture 6 annexes). In the plateau the soil texture is loamy sand on
the top soil (10 cm deep) with brown to dark brown color. In the subsoil (20 cm deep) the
texture is mostly loamy sand with an average of 12 % clay content with reddish brown to
brown color. In the glacis the texture is sandy in the top soil and sandy to loamy sand in
the sub soil with an average of 90 % sand. The wet Munsell color is generally from
reddish brown to brown color. In the plateau and the glacis the soils overlie a layer of
cuirass. In the bas fond, the top 10 cm are generally sandy loam with dark brown color.
From 10 to 20 cm deep, a layer of pure sand is generally found. High clay content is
mostly found in deeper profile (more than 40 cm deep) with dark color due to high
organic matter content. The total fine soil fraction (clay + silt) is higher in the plateau
(16.3 %) decreasing down slope and attain its lowest value in the bas fond (9.5 %) where
coarse material content is mostly found in the upper 20 cm. The bulk density between 1.7
and 1.8 is lower in the plateau where clay + silt content is higher.
3.2 Land use descriptions
Overall seven different types of land use have been identified:
Continuous rotation cereal peanut without or low external input (CRCPLI)
Continuous rotation cereal peanut with high external input (CRCPHI)
Permanent fallow in the plateau (PFP)
Permanent fallow in the terrace (PFT)
Permanent fallow in the bas fond (PFBF)
Continuous cereal cultivation in the bas fond (CCBF)
Continuous cereal cultivation under parkland (CCP).
39 plots have been identified in this study with a total of 94 soil samples. These plots are
situated in different positions in the landscape in the 3 selected villages of the study area
(table 1).
iv
Table 1: Identification of different types of land use in the Nioro area.
Land use
CRCPLI
Farms reference
Locations
D12, D21, D31, D13, D22, Djiguimar
D32, D14, D33, D23, D24,
D34.
Pa12, Pa13, Pa14, Pa15, Paoskoto
Pa16, Pa17, Pa18, Pa22,
Pa23, Pa24, Pa25.
PFP
Prokhane
Pr14, Pr15.
Pr11, Pr12, Pr13, Pr21, Prokhane
Pr22.
D11
Djiguimar
PFT
PFBF
Pa11
D15
D16
Paoskoto
Djiguimar
Djiguimar
CCBF
Pa110
D25, D35.
Paoskoto
Djiguimar
CCP
Pa26
Pa19
Paoskoto
Paoskoto
Pr31
Prokhane
CRCPHI
Land management is generally the same for all farmers in the area. It is characterized by
very low or no input of mineral fertilizer or organic matter. The peasants have very
limited means to buy fertilizers, and some of them who have manure lack transportation
mean and/or labor to bring organic matter in the fields, that’s why manure is generally
devoted to fields near the villages. As discussed earlier crop residues are removed from
the fields or simply burnt in situ prior to seedbed preparation. Superficial tillage (less than
10 cm) using hoe with animal traction is mostly practiced in the area.
v
3.3 Carbon stocks
3.3.1 Carbon distribution and pH along the landscape
The results showed that total carbon content in the upper 20 cm range from 0.49 % to
0.62 % in the rocky plateau, between 0.20 and 0.69 % in the glacis, between 0.34 % and
1.97 % in the terrace and between 0.15 % and 0.68 % in the bas fond (table 2). Data show
a relatively high organic carbon content in the plateau (0.49 %) decreasing down slope in
the glacis (0.37 %) increasing again at the lower slope on the terraces and decrease again
in the upper 20 cm of the bas fond. Terraces occur sometimes just before the bas fond and
is a transition area between glacis and the lowland. Wind and water erosion are most
prevalent in the glacis and may have increased the loss of organic matter, which may
have settled down slope in the terrace area, a flat area followed by a steep slope ending to
the bas fond. Sedimentation may take place herein and the accumulation of organic
matter in that part of the landscape may be explained by material transported with water
runoff from the upper land. Erosion directly removes soil C and breaks down soil
aggregates, exposing physically protected organic matter to decomposition and loss.
Organic-rich soil from the surface layer is carried away to the lower land. Erosion
intensity depends however on many factors: they are included in the universal soil-loss
equation (Brady, 1990). These factors are, climatic erosivity (rainfall and runoff), slope
length, slope steepness, land cover and land management.
Considerable variation is noticed however between terraces samples sites in the organic
carbon content (between 0.34 and 1.97; SD= 0.51). This is due to a parkland situated in a
terrace in the village of Hamdallahi in the Paoskoto transect , which show a carbon
content as high as 1.97 % on the top 10 cm. Parklands are generally near the villages
mostly situated in the terraces which are the most favorable area in the landscape for
population settling.
In the bas fond the bulk of the carbon is found in the deeper horizons. This explains the
low carbon content found in the upper 20 cm. Water stagnates herein and moves
downward into the soil, it causes both mechanical and chemical translocations of material
(organic matter and clay). This process moves fine particles and dissolved substances to
lower levels in the soil profile. This process called illuviation, proceeds to deposition of
fine particles at the lower level. This layer (10 to 20 cm) possibly represents an eluviated
horizon where the bulk of fine particles have moved downward with water infiltration
(picture 6 in annexes) . Another possible explanation is that with periodical water
flooding in the bas fond, organic matter with fine particles may also be deposited with
water runoff overlaid by a sandy layer. This situation may be repeated seasonally and this
may be the reason of high content of organic matter in deeper profile. However some top
soil of the bas fond may be very rich in fine particles and in organic matter. This may
happen when new organic material is deposited with lateral movement of water and not
vi
yet overlaid by sand. This is possibly the case in one of the transect in Djiguimar bas
fond, where organic carbon content increasing with fine particles probably deposited at
the same time is as high as 0.68 %. It also occurred to find pure sand on the top soil
(picture 8 in annexes), possibly deposited with the lateral movement of water.This
situation makes the bas fond the more complicated part of the landscape. Figures 20 to 26
show the distribution of carbon, fine particles and sand in the profile of the bas fond in
the different forms of landscape.
In overall, the pH ranges between 4.9 and 5.6 with lower values in the glacis where loss
of organic material from the top soil is likely to increase soil acidity. The higher value for
average pH (5.6) is found in the terrace largely influenced by the high pH in the parkland
(7.4).
However individual analysis of the transects may show some exceptions in the carbon
distribution. When this happens it’s generally due to many factors: a better land cover, a
specific land management practice for erosion control, a difference in slope length or in
slope steepness (Brady, 1990). The relationship between erosion intensity and slope
characteristics is out of the scope of this study but examples are shown in figures 16, 17,
and 18 with three different cases : short sloping landscape (602 m, 5%) ; long gentle
landscape (1810 m, < 1%) ; short sloping landscape (685 m, <1 %). Data show higher
gradient difference in organic carbon content between plateau and the glacis in the long
gentle slope (38 %), followed by the short sloping landscape (33 %) and the lowest value
(5 %) is found in the short gentle slope.
Table 2: Soil properties along the landscape in the upper 20 cm.
Toc1 %
Bd2
pH
n
______________________________________________________________________________________
____
Plateau
0.49± 0.13
13.5± 5.3
1.7± 0.12
5.3± 0.2
3
Glacis
0.37± 0.09
13.0± 3.5
1.8± 0.07
4.9± 0.3
20
Terrace
0.74± 0.51
14.0± 2.2
1.8± 0.06
5.5± 0.9
4
Bas fond0.40± 0.17
10.5± 3.7
1.7± 0.06
5.2± 0.2
5
1
Clay + silt %
total organic carbon ; 2 bulk density
Table 3: Carbon distribution (%) in three different landscapes in the upper 20 cm
Position
Short sloping
long gentle slope
vii
short gentle slope
______________________________________________________________________________________
____
Plateau
0.58
0.56
0.34
Glacis
0.39
0.35
0.32
Terrace
0.66
1.15
0.49
Bas fond0.40
0.40
0.44
3.3.2 Distribution of organic carbon in different land use
Data show a range in organic carbon content at 10 cm between 0.43 % and 1.26 % and
between 0.27 % and 0.79 % in the subsoil (at 20 cm depth). The highest value of organic
carbon in the top soil is found in the CCP land use while the lowest value is in the
CRCPLI land use. The high content of organic carbon in the parkland with a low content
of clay and silt make this amount of carbon unstable and easily decomposable with the
high temperature in the area.
In general the concentration of organic carbon is lower in the subsoil compared to the top
soil. This is possibly due to the influence of fresh organic matter inputs on the top soil
from straws, dead roots, leaf litter and manure in some cases. However the data show
correlation between organic carbon and clay content in the sub soil (r = 0.72). But the
correlation is higher with silt fraction (r = 0.80). This indicates that clay and also silt play
a key role in organic carbon stabilization. Carbon in the subsoil is mainly bound to soil
micro-aggregates and is protected from decomposition. As reported by Bationo (2001)
fine fractions, higher in the subsoil are important soil component in the direct
stabilization of organic molecules. However this protection from decomposition can be
easily disrupted by management such as tillage.
For the subsoil the highest value of organic carbon is found in PFT (permanent fallow on
terrace) while the lowest value is found in PFBF (Figure 19). Soil carbon decreased with
depth which is normally expected, except for the PFT, where soil organic carbon content
increased with depth a least until 30 cm which have been effectively sampled and
measured. This is unlikely to happen but the hydrolysis of the SOC between 20 to 30 cm
shows a large part of this carbon is recalcitrant (part 3) ; this is likely to be charcoal
accumulation. As burning is an old practice in the area, charcoal from crop residues
burning products may be transported with water or wind from the upper land and
deposited in the terrace. Charcoal may also be produced in situ and further overlaid with
a new layer of deposited material. This situation is the only one we encounter in the area
and could not represent the general situation of permanent fallow in terrace but was
interesting to show how variable could be the soils standing in different positions of the
landscape.
Table 4: Distribution of carbon under different types of land use
viii
Land use
Management
PH
Carbon %
Clay + silt
%
______________________________________________________________________________________
___
Depth (cm)
10
20
10
20
10
20
________________________________________________________________________
___
CCBF
n=3
no fertilizer, no tillage
5.2
5.1
0.51
0.36
11
organic input, no tillage
6.7
6.2
1.26
0.42
9
fertilizer input, tillage
5.0
4.8
0.48
0.38
12
no fertilizer, no tillage
5.1
4.8
0.43
0.34
11
undisturbed1
5.5
5.3
0.48
0.27
10
undisturbed2
5.4
5.1
0.62
0.52
15
undisturbed3
5.2
5.1
0.65
0.71
13
11
CCP
n=2
12
CRCPHI n = 5
15
CRCPLI n = 24
15
PFBF
n=2
9
PFP
n=2
18
PFT
n=1
14
1
hydromorphic soils seasonally water flooded, uncultivated
rocky plateau, uncultivated
3
terrace, uncultivated
2
To study the relationship between carbon input and total organic carbon content, the seven types
of land use identified in this study are ranked according to their carbon input. The lowest carbon
input land use will be given the lowest score and the highest score is given to the highest carbon
input land use. Scores are from 1 to 7. Thus, CRCPLI<CCBF<PFBF<CRCPHI<PFP<PFT<CCP
is the ranking made according to the estimate of carbon input for each type of land use. Data
show increasing carbon content in the upper 20 cm with increasing carbon input (table 5, figure
10). A strong relationship exists between carbon input and carbon content with a high correlation
factor r = 0.90 (p < 0.006). This gives insight how land use is important in organic matter
dynamics and in carbon content prediction for a given soil.
Table 5: Average carbon content in the upper 20 cm in different types of land use ranked according to their
carbon input
Rank
Land use
Carbon (%)
Clay
+silt (%)
______________________________________________________________________________
____
1
CRCPLI
0.39
13
2
CCBF
0.44
11
ix
3
4
5
6
7
PFBF
CRCPHI
PFP
PFT
CCP
0.38
0.43
0.57
0.68
0.84
.
Carbon content
1
0,8
0,6
0,4
0,2
0
1
2
3
4
5
6
7
Carbon input rank
Figure 9 : carbon content (%) in the upper 20 cm and carbon input
x
10
14
17
14
11
3.4 Relationship between total carbon and other soil properties
3.4.1 Carbon and nitrogen
In the top 10 cm average total nitrogen content in the different types of land use range
between 0.029 % and 0.096 % (mean = 0.054 %) Carbon nitrogen ratio (C/N) are
between 10 and 20 (mean = 15). Data show a high correlation between total carbon and
total nitrogen (r = 0.9 p < 0.02). This indicates that the bulk of the soil nitrogen is tied
up in soil organic carbon. This is in total agreement with Stevenson (1982) who stated
that over 90 % of nitrogen in the soil is bound to organic matter, from which a large
amount becomes available to plants only after mineralization. The results of nitrogen
content and C/N ratio in the top 10 cm are shown in table 4. The graph (figure 11) shows
the relationship between total carbon and total nitrogen.
Table 6: Total carbon and total nitrogen in different types of land use
Land use
Total nitrogen %
Total carbon %
C/N
________________________________________________________________________
___
CCBF
CCP
CRCPHI
CRCPLI
PFBF
PFP
PFT
0.029
0.096
0.043
0.046
0.059
0.055
0.082
0.55
1.02
0.67
0.57
0.67
0.74
0.83
20
11
16
14
12
15
10
0.12
Total nitrogen %
0.1
R2 = 0.8692
0.08
0.06
0.04
0.02
0
0
0.2
0.4
0.6
0.8
1
Total carbon %
Figure 10: Relationship between total carbon and total nitrogen
xi
1.2
3.4.2 Carbon and pH
Soil pH is a measure of a soil solution’s acidity and alkalinity that affects solubility and
availability of nutrients in the soil (Mc Cauley et al, 2003). The exchange reactions
between soil solution and the soil particles surfaces are the main regulators of soil pH
(Coleman et al, 1989). Although processes such as the amount of CO2 dissolved in the
soil solution and the formed organic acids by microbial decomposition influence soil
acidity, the relative amounts of basic and acidic exchangeable cations determine its actual
value (Coleman et al, 1989). Our data show a weak relationship between pH and carbon
(r = 0.12) but a high correlation (r = 0.91) exists between pH in one hand and carbon and
total fine particles (clay + silt) in the other hand. The conclusion is that soil pH does not
determine the organic carbon of the soil, but organic matter content in part can predict the
pH of the soil. The relation is as follow
pH = 2.380*carbon - 0.051*(clay + silt) with (p = 0.011) at 95 % confidence.
3.4.3 Carbon and total fine fractions
Soils with high clay and silt content have generally high organic matter content. This is
attributed to restricted aeration in finer-textured soils, reducing the rate of organic matter
decomposition. Additionally, plant growth is greater in fine textured soils, resulting in a
larger return of residues to the soil (Mc Cauley et al, 2003). Our data do not show
significant relationship between carbon and total fine fractions in the whole data set but
there is a high correlation (r = 0.75 p < 0.03) between the two parameters in the subsoil
(10 to 20 cm depth). The strong relationship between carbon and fine particles in the
subsoil give insight how more protected is that part of the SOC. In the top soil rich in
sand, it is likely that organic carbon less protected are easily transported with wind and
water runoff.
3.4.4 Carbon and bulk density
Soil is composed of solid particles of different sizes (minerals and organic matter) often
"glued" together into tiny aggregates by organic matter, mineral oxides and charged clay
particles. The gaps between the particles link together into a meandering network of
pores of various sizes. Through this pore space the soil exchanges water and air with the
environment. The movement of air and water also allows for heat and nutrients to flow.
The number and size of pores directly relates to soil organic matter content, texture and
structure. Bulk density is the weight of a given volume of soil which includes the pore
spaces. Coarse textured soils will usually have a higher bulk density because they have
less pore space than fine textured soils. Bulk density is an important property of soils
since it affects how easily plant roots can penetrate the soil when they propagate.
xii
Our data show that bulk density could be predicted by soil organic matter content (r =
0.51) but the correlation is stronger if clay content is associated in the prediction (r =
0.91, p< 0.01). This indicates that bulk density depends on soil minerals and also on soil
organic matter.
3.4.5 Total organic carbon, recalcitrant carbon and nitrogen
Recalcitrant carbon
The relative abundance of recalcitrant carbon and nitrogen are simple and useful
indicators of organic carbon and nitrogen quality (Rovira et al, 2002).
A regression analysis was performed with total carbon and recalcitrant carbon and
significant correlation (r = 0.97 p = 0.000) was observed (figure 12). This may indicate
that the proportion of stable carbon depends on the total carbon pools. Figure 13 shows
relationship between recalcitrant carbon and recalcitrant nitrogen. No significant
relationship exists however between recalcitrant carbon pool and the total fine fractions
of the soil. This indicates that this portion of carbon is not completely physically
protected in soil micro-aggregates; a large part may be possibly indecomposable
according to its inherent properties. This pool may have a residence time of thousand of
years and will probably not be disturbed by tillage or by any other form of land
management. This pool can be considered as irreversibly sequestered into the soil for a
long time.
2.000
1.800
1.600
1.400
1.200
1.000
0.800
0.600
0.400
0.200
0.000
0
0.5
1
1.5
2
Total carbon
Figure 11: Relationship between total carbon and recalcitrant carbon.
Table 7: Land use and carbon and nitrogen recalcitrance on the topsoil (upper 10 cm)
Land use
total C
total N
Rec C
Rec N
%Rec C
%Rec N
_____________________________________________________________________________________
CCBF
0.55
0.029
0.31
0.025
56
86
CCP
1.02
0.096
0.53
0.035
52
36
CRCPHI
0.67
0.043
0.44
0.054
65
125
CRCPLI
0.57
0.046
0.33
0.027
58
58
PFBF
0.67
0.059
0.39
0.036
58
61
PFP
0.74
0.055
0.35
0.039
47
70
xiii
PFT
0.83
0.082
0.49
0.020
59
24
Table 8: Land use and carbon and nitrogen recalcitrance in the subsoil (20 cm depth)
Land use
total C
total N
Rec C
Rec N
%Rec C
%Rec N
______________________________________________________________________________________
____
CCP
0.52
0.039
0.34
0.058
65
148
CRCPHI
0.53
0.040
0.35
0.048
66
120
CRCPLI
0.50
0.041
0.28
0.031
56
75
PFT
1.03
0.074
0.66
0.041
64
55
PFP
0.61
0.046
0.28
0.021
45
46
Table 9: Land use and carbon and nitrogen recalcitrance in the bas fond subsoil (40 cm depth)
Land use
total C
total N
Rec C
Rec N
%Rec C
%Rec N
______________________________________________________________________________________
____
CCBF
0.29
0.024
0.15
0.051
52
212
PFBF
0.39
0.032
0.20
0.032
51
100
Table 10: Carbon and nitrogen recalcitrance in the whole profile o a bas fond (100 cm depth)
Depth (cm)
total C
total N
Rec C
Rec N
%Rec C
%Rec N
______________________________________________________________________________________
____
10
0.55
0.029
0.31
0.025
56
86
40
0.29
0.024
0.15
0.051
52
212
60
0.48
0.015
0.32
0.004
67
26
100
0.95
0.030
0.67
0.013
70
43
No significant relationship between soil depth and recalcitrant carbon is found (p =
0.183). In spite of this result resistance to decomposition may depend on depth but this
xiv
could be involved to a lower microbial activity to certain depth and not to the carbon
inherent properties. This is in total agreement with the finding of Rovira et al (2002).
No direct relationship can be claimed however between land use and recalcitrance.
Agricultural management seems to have no effect on the passive pool. The slow pool
(protected pool) may show relationship with land use but this pool is extracted but not
quantified in this study for technical reason. It can be noticed however that PFP land use
has less proportion of recalcitrant carbon (46 %) and the high input land use (CRCPHI)
has recorded the highest proportion of recalcitrant carbon (66%).
Recalcitrant Nitrogen
In the recalcitrant pool there is always a decrease of carbon for all samples but we found
an increase in nitrogen content in the recalcitrant sample compared to the original sample.
This happened mostly in sub soil samples (20 cm and 40 cm) and in a top soil for the high
input land use. This was not the case for 60 and 100 cm depth. According to Rovira et al
(2002) this may happen because of the short time of hydrolysis to achieve a complete
release of hydrolysable N. Stevenson (1982) recommends hydrolysis times of 12 to 24 h
with hydrochloric acid which is more efficient than sulfuric acid used in this study.
0.150
R2 = 0.2774
0.100
0.050
0.000
0.000
0.500
1.000
1.500
2.000
Recalcitrant carbon
Figure 12: Relationship between recalcitrant carbon and recalcitrant nitrogen
3.5 Potential for carbon sequestration
The results for total carbon sequestrated in the upper 20 cm are described in average in
each position through the landscape and for each land use in the area.
Taking in consideration the carbon stocks in the landscape regardless the land use, data
showed that total carbon range in the upper 20 cm from 8.5 t ha-1 to 39.1 t ha-1 with an
average of 15.2 t ha-1 and a standard deviation of 6.04. The minimum carbon sequestrated
is in the glacis and the bas fond (upper 20 cm considered) and the maximum carbon is in
the terrace. In the Plateau data ranged between 11.6 t ha-1 and 19.5 t ha-1 (mean = 16.5 SD
± 4.3) while in the glacis they are between 8.5 and 21.6 t ha-1 (mean = 12.9 SD ± 3.1). In
the terrace they range between 14.9 and 39.1 t ha-1 (mean = 23.9 SD ± 9.4) and in the bas
fond carbon stocks are between 8.5 and 21 t ha-1 (mean = 14.2 SD± 4.5) (table 7).
xv
When regrouping data by land use type, highest carbon stocks are found in the CCP
(continuous cereal in parkland) land use (28.9 t ha-1) which seems to be related to the
considerable amounts of organic matter input with manure. The lowest carbon stock is
found in the CRCPLI (17.2 t ha-1) which is probably due to the lowest external input
(mineral fertilizer, and organic matter) and in the upper 20 cm of the CCBF which is
possibly due to the high sand content in this layer in the bas fond (table 11). The results
found in this study (table 10) are in the same line as those found in the west central part
of Senegal which range from 4.5 and 18 t ha-1 in the upper 20 cm (Tiessen et al, 1998). In
a recent study in the same area, Tschakert et al (Article in press) also found values for
soil carbon in the 20-40 cm horizon which ranged between 2.8 and 29.8 t ha-1.
Table 11: Carbon stocks in the upper 20 cm in t ha-1 in different positions of the landscape
Position
min carbon
max carbon
average
SD
______________________________________________________________________________________
___
Plateau
11.6
19.5
16.5
4.3
Glacis
8.6
21.6
12.9
3.1
Terrace
14.9
39.1
23.9
9.4
Bas fond
8.6
21.0
14.2
4.5
Table 12: Carbon stocks in the upper 20 cm in t ha-1 in different types of land use
Land use
SD
min carbon
max carbon
average
________________________________________________________________________
___
CCBF
6.2
CCP
14.4
CRCPHI
2.1
CRCPLI
3.5
8.6
21.0
14.9
18.7
39.1
28.9
11.7
17.2
14.9
8.6
23.1
13.7
xvi
PFBF
1.0
PFP
0.6
PFT
---
12.5
13.9
13.2
18.6
19.5
19.0
24.8
24.8
24.8
IV Conclusion
The data analysis has shown that the range of carbon sequestration potential in the Basin
Peanut of the Nioro area varies considerably depending on the position in the landscape,
the land use type and the land management practices. Terrace is the most promising area
for carbon sequestration in the landscape. In the glacis where carbon is mostly depleted,
specific land management practices like erosion control practice and no till cultivation are
needed to minimize material removal from the top soil. The upper 20 cm of the bas fond
contain a low amount of carbon which generally moved down in deeper profile replaced
by a layer of sand. This carbon is generally well protected and is considered as
irreversibly sequestrated. As long as rocks are standing in the plateau, this area will be
uncultivated and would be a promising potential area for carbon sequestration.
The more popular land use in the area is the continuous rotation cereal peanut with low
input (crcpli) which is practiced in the major part of the area. With the high pressure
exerted on the land, fallow is not practiced anymore in the area; it is always an occasional
practice and is an exception wherever it exists. Seeds crop or labour shortage are the main
reasons for a normal field to be left uncultivated. High input agriculture has the
advantage to provide more biomass but the drawback is that crop residues are not
returned into the soil and represent considerable organic carbon losses. The crop residues
produced in high input agriculture, if returned into the soil would represent a high C input
for the soil which would exceeds litter fall in natural agro-ecosystems (Coleman et al,
1989).
In the Peanut Basin, large areas are affected by land degradation mostly due to water
erosion, wind erosion, improper land management which induced chemical and physical
land deterioration (Batjes, 2001). Those degraded lands are potentially ideal areas for
carbon sequestration through adapted land management, provided that agro-ecological
and socio-economic factors are in place (Batjes, 2001). Soil carbon models are useful
tools to assess possible consequences of a range of land management options on soil
carbon pools and its evolution over time. They would be recommended for a future study
in the area for a thorough evaluation of the rate of carbon sequestrated in relation to land
management options.
xvii
References
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GIS and the CENTURY model. Journal of Arid Environments 54, 633-651.
Bationo A., 2001. Soil Organic Carbon management for sustainable land use in SudanoSahelian West Africa. Nutrient Cycling in Agroecosystems 61, 131-142.
Batjes N.H., 2001. Options for increasing carbon sequestration in West African soils: An
exploratory study with special focus on Senegal. Land degradation and development 12,
131-142.
Brady N. C.,1990. The Nature and properties of SOILS 10th Edition. In Macmillan
Publishing Company, New York. 621 pp
Coleman D.C., Oades J. M., Uehara G., 1989. Dynamics of Soil Organic Matter in
Tropical Ecosystems. Published by NifTAL Project. 249 pp
Hill M.J., 2003. Generating generic response signals for scenario calculation of
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using CENTURY. Environmental Modelling & Software 18, 899-913.
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a series of syllabi Part 5 Soil Analysis Procedures. Department of Soil Science and Plant
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Iyamuremye F., Gewin V., Dick R.P., Diack M., Sene M., Badiane A., Diatta M., 2000.
Carbon, Nitrogen and Phosphorus Mineralization Potential of Native Agroforestry Plant
Residues in Soils of Senegal. Arid Soil Research and Rehabilitation 14, 359-371.
Manlay R. J, Masse D, Chotte J. L., Ciornei G., Feller C., Kairé M., Fardoux J.,
Pontanier R., 2002. Carbon, nitrogen and phosphorus allocation in agro-ecosystems of a
West African savanna. II. The soil component under semi-permanent cultivation.
Agriculture, Ecosystems and Environnement 88, 233-248.
Manlay R. J., Kairé M., Masse D., Chotte J. L., Ciornei G., Floret C., 2002. Carbon,
nitrogen and phosphorus allocation in agro-ecosystems of a West African savanna. I. The
plant component under semi-permanent cultivation. Agriculture, Ecosystems and
Environnement 88, 215-232.
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Mc Cauley A., Jones C., Jacobsen J., 2003. Soil pH and Organic Matter. A self study
course from the MSU extension service continuing education series. Montana
State University.12 pp.
Oldeman, L. R., Hakkeling, R. T. A. and W. G. Sombroek. 1990. World Map of the
Status of Human-Induced Soil Degradation; ExplanatoryNote. (The) Global Assessment
of Soil Degradation, ISRIC and UNEP incooperation with the Winand Staring Centre,
ISSS, FAO and ITC; 27 pages.
Olivier R., 1978. Méthodes d’analyse des sols, des eaux et des plantes en usage au CNRA
de Bambey recueillis par R. Olivier. Centre National de Recherches Agronomiques,
Institut Sénégalais de Recherches Agricoles. Délégation Générale à la Recherche
Scientifique et Technique. République du Sénégal, Primature 70 pp.
Pieri C., 1969. Etude Pédologique de la Région de Nioro du Rip. Rapport Volume I.
Centre National de Recherches Agronomiques de Bambey.
Pieri C., 1992. Fertility of Soils, A Future for Farming in the West African Savannah.
Ministere de la Cooperation-CIRAD, translated from French by Philip Gething, original
title Fertilité des terres de savanes. In Springer-Verlag. Berlin. 346 pp
Plaster E. J., 1992. Soil Science and Management 2nd Edition
Rovira P., Vallejo V.R., 2002. Labile and Recalcitrant pools of carbon and nitrogen in
organic matter decomposing at different depths in soil: an acid hydrolysis approach.
Geoderma 107, 109-141.
Singer M. J.,. Munns D. N., 1999. Soils an introduction 4th Edition
Stevenson F. J., 1982. Nitrogen in Agricultural soils. American Society of America,
Publisher, Madison Wisconsin USA. 940 pp
Tiessen H., Feller C., Sampaio E.V.S.B., Garin P., 1998. Carbon sequestration and
turnover in semi arid savannas and dry forest. Climatic Change 40, 105-117.
Tschakert P., 2003. The costs of soil carbon sequestration: an economic analysis for
small-scale farming systems in Senegal. In press in Agricultural Systems. 27 pp.
xix
Tschakert P., khouma M., Sene M.. Unpublished. Biophysical Potential for Soil Carbon
Sequestration in the Old Peanut Basin of Senegal.
Annexes
xx
SOIL DATA
xxi
Transect
Parcel
Latitude
Longitude
Position
Rotation
L use
Depth
BD
PH
TOC
Clay
13.8219
-15.7758
Plateau
Fal/Fal
PFP
10
1.86
5.3
0.62
9.3
8.3
Plateau
Fal/Fal
PFP
20
1.48
4.9
0.54
14.0
6.8
Glacis
P/Mi
CRCPLI
10
1.74
5.2
0.69
8.8
8.7
Glacis
P/Mi
CRCPLI
20
1.68
5.0
0.57
12.8
7.7
Glacis
P/Mi
CRCPLI
10
1.80
5.0
0.50
6.5
7.2
Glacis
P/Mi
CRCPLI
20
1.91
4.9
0.43
11.5
6.3
Glacis
P/Mi
CRCPLI
10
1.81
5.1
0.44
6.5
6.3
Glacis
P/Mi
CRCPLI
20
1.87
4.9
0.37
10.5
6.0
terrace
Fal/Fal
PFT
10
1.76
5.2
0.65
6.0
6.8
5
terrace
Fal/Fal
PFT
20
1.89
5.1
0.71
7.8
6.5
5
terrace
Bas
fond
Bas
fond
Bas
fond
Bas
fond
Fal/Fal
PFT
30
5.0
1.45
9.3
8.7
Fal/Fal
PFBF
10
1.81
5.6
0.54
5.5
5.2
Fal/Fal
PFBF
20
1.81
5.5
0.15
3.5
2.5
Fal/Fal
PFBF
30
5.3
0.09
3.0
2.0
Fal/Fal
PFBF
40
4.8
0.25
6.0
5.0
Glacis
P/Mi
CRCPLI
10
1.78
5.0
0.33
7.0
4.2
Glacis
P/Mi
CRCPLI
20
1.99
4.5
0.35
11.3
4.2
Glacis
P/Mi
CRCPLI
10
1.80
5.0
0.47
6.5
6.2
Glacis
P/Mi
CRCPLI
20
1.96
4.9
0.35
11.0
5.5
Glacis
P/Mi
CRCPLI
10
1.82
5.2
0.46
7.0
7.3
Glacis
P/Mi
CRCPLI
20
1.78
4.8
0.29
9.8
6.4
terrace
P/Mi
CRCPLI
10
1.80
4.8
0.29
8.1
4.4
terrace
Bas
fond
Bas
fond
Bas
fond
Bas
fond
P/Mi
CRCPLI
20
1.73
4.6
0.20
12.4
4.6
Mi/Mi
CCBF
10
1.78
5.3
0.68
7.6
5.5
Mi/Mi
CCBF
20
1.63
5.1
0.55
7.1
5.1
Mi/Mi
CCBF
30
4.8
1.12
11.1
11.1
Mi/Mi
CCBF
40
4.9
1.31
13.4
15.5
Glacis
P/Mi
CRCPLI
10
1.83
4.6
0.40
6.5
3.9
Glacis
P/Mi
CRCPLI
20
1.75
4.5
0.34
9.4
3.5
Glacis
P/Mi
CRCPLI
10
1.65
5.0
0.40
5.3
4.7
Glacis
P/Mi
CRCPLI
20
1.84
4.7
0.30
8.0
6.1
Glacis
P/Mi
CRCPLI
10
1.79
4.7
0.28
4.9
2.4
Glacis
P/Mi
CRCPLI
20
1.79
4.4
0.32
8.4
3.1
terrace
P/Mi
CRCPLI
10
1.77
5.1
0.65
7.4
5.0
terrace
Bas
fond
Bas
fond
Bas
fond
Bas
fond
Bas
fond
Bas
fond
P/Mi
CRCPLI
20
1.84
5.0
0.63
8.6
6.6
Mi/Ma
CCBF
10
1.80
5.3
0.33
4.4
3.9
Mi/Ma
CCBF
20
1.71
5.3
0.16
2.1
2.0
Mi/Ma
CCBF
30
5.4
0.10
1.7
0.6
Mi/Ma
CCBF
40
5.4
0.07
1.6
0.5
Mi/Ma
CCBF
50
5.1
0.21
3.2
2.8
Mi/Ma
CCBF
60
4.9
0.40
6.3
6.1
1
1
1
1
1
2
1
2
1
3
1
3
1
4
1
4
1
5
1
1
1
6
1
6
1
6
1
6
2
1
2
1
2
2
2
2
2
3
2
3
2
4
2
4
2
5
2
5
2
5
2
5
3
1
3
1
3
2
3
2
3
3
3
3
3
4
3
4
3
5
3
5
3
5
3
5
3
5
3
5
13.8389
13.8478
13.8619
13.8828
13.9064
-15.7667
-15.7608
-15.7536
-15.7542
-15.7542
13.8283
-15.7342
13.8386
-15.7261
13.8564
13.8664
13.8939
13.8389
13.8547
13.8736
13.8908
13.6675
-15.7269
-15.7253
-15.7172
-15.7805
-15.7764
-15.7794
-15.7797
-15.7947
xxii
Silt
3
Bas
fond
5
Mi/Ma
CCBF
100
5.0
0.79
10
9.9
Table 12: Djiguimar data set
Transect
Parcel
Latitude
Longitude
Position
Rotation
L use
Depth
BD
PH
TOC
Clay
Silt
1
1
13.9839
-15.8700
Plateau
Fal/Fal
PFP
10
1.66
5.5
0.62
7.4
4.6
1
1
Plateau
Fal/Fal
PFP
20
1.68
5.2
0.49
11.1
4.0
1
2
13.9880
-15.8533
Glacis
P/Mi
CRCPLI
10
1.80
5.4
0.40
6.6
3.9
1
2
Glacis
P/Mi
CRCPLI
20
1.76
5.0
0.33
9.4
3.4
1
3
Glacis
P/Mi
CRCPLI
10
1.71
5.2
0.49
7.6
9.0
1
3
Glacis
P/Mi
CRCPLI
20
1.71
5.0
0.34
11.0
8.1
1
4
Glacis
P/Ma
CRCPLI
10
1.66
5.4
0.50
5.9
8.2
1
4
Glacis
P/Ma
CRCPLI
20
1.82
4.7
0.33
9.2
6.5
1
5
Glacis
P/Mi
CRCPLI
10
1.76
5.3
0.34
4.5
4.4
1
5
Glacis
P/Mi
CRCPLI
20
1.74
4.9
0.26
9.1
4.4
1
6
Glacis
P/Mi
CRCPLI
10
1.80
4.7
0.30
7.4
2.6
1
6
Glacis
P/Mi
CRCPLI
20
1.83
4.5
0.25
11.6
2.7
1
7
Glacis
WM/P
CRCPLI
10
1.73
5.1
0.30
3.9
3.1
1
7
Glacis
WM/P
CRCPLI
20
1.71
4.4
0.25
9.1
2.9
1
8
Glacis
Ma/S
CRCPLI
10
1.78
5.0
0.40
8.1
5.8
1
8
Glacis
Ma/S
CRCPLI
20
1.86
5.1
0.42
7.2
5.6
1
9
terrace
Mi/Mi
CCP
10
1.68
7.4
1.97
5.9
4.5
1
9
terrace
Mi/Mi
CCP
20
1.77
6.2
0.34
9.0
5.2
1
10
Bas fond
Fal/Fal
PFBF
10
1.75
5.4
0.42
3.8
5.9
1
10
Bas fond
Fal/Fal
PFBF
20
1.73
5.1
0.38
6.4
5.6
1
10
Bas fond
Fal/Fal
PFBF
30
5.1
0.23
9.4
3.6
1
10
Bas fond
Fal/Fal
PFBF
40
5.0
0.19
9.6
4.0
2
1
Plateau
Ma/Mi
CRCPLI
10
1.73
5.6
0.42
3.1
3.4
2
1
Plateau
Ma/Mi
CRCPLI
20
1.63
5.2
0.27
6.9
2.1
2
2
Glacis
P/Mi
CRCPLI
10
1.78
5.2
0.35
3.4
1.8
2
2
Glacis
P/Mi
CRCPLI
20
1.73
4.7
0.24
7.2
1.4
2
3
Glacis
P/Mi
CRCPLI
10
1.69
5.2
0.33
4.1
3.0
2
3
Glacis
P/Mi
CRCPLI
20
1.67
4.9
0.28
7.5
2.8
2
4
Glacis
Ma/Mi
CRCPLI
10
1.68
5.2
0.41
6.5
5.4
2
4
Glacis
Ma/Mi
CRCPLI
20
1.74
5.0
0.33
10.4
5.1
2
5
terrace
P/Mi
CRCPLI
10
1.81
5.1
0.57
7.4
7.6
2
5
terrace
P/Mi
CRCPLI
20
1.76
4.8
0.40
11.1
6.7
2
6
Bas fond
P/Mi
CCBF
10
1.78
5.1
0.51
6.6
5.9
2
6
Bas fond
P/Mi
CCBF
20
1.67
4.9
0.37
11.1
5.9
2
6
Bas fond
P/Mi
CCBF
30
4.9
0.24
15.6
4.7
2
6
Bas fond
P/Mi
CCBF
40
4.8
0.19
18.2
4.6
13.9889
-15.8383
13.9900
-15.8194
13.9950
-15.7958
13.9967
13.9989
14.0078
-16.0436
-16.0197
-15.9925
14.0358
-15.9183
14.0319
-15.8608
14.0222
-15.9561
14.0380
-15.9505
14.0561
13.8114
13.8339
13.8542
-15.9380
-15.9339
-15.9228
-15.9097
Table 13: Paoskoto data set
xxiii
Transect
Parcel
Latitude
Longitude
Position
Rotation
L use
Depth
BD
PH
TOC
Clay
Silt
1
1
13.9325
-16.0111
terrace
Ma/Mi/P
CRCPHI
10
1.68
5.3
0.39
4.4
2.7
1
1
terrace
Ma/Mi/P
CRCPHI
20
1.76
4.8
0.29
8.0
4.2
1
2
terrace
Ma/Mi/P
CRCPHI
10
1.73
5.1
0.54
5.7
5.6
1
2
terrace
Ma/Mi/P
CRCPHI
20
1.78
5.0
0.44
8.9
5.9
1
3
terrace
Ma/Mi/P
CRCPHI
10
1.73
4.7
0.51
7.1
4.6
1
3
terrace
Ma/Mi/P
CRCPHI
20
1.67
4.7
0.41
10.9
4.5
1
4
terrace
P/Mi
CRCPLI
10
1.70
5.1
0.55
8.4
5.9
1
4
terrace
P/Mi
CRCPLI
20
1.67
4.7
0.37
13.9
5.1
1
5
terrace
P/Mi
CRCPLI
10
1.73
5.2
0.47
6.6
5.0
1
5
terrace
P/Mi
CRCPLI
20
1.75
4.9
0.35
11.5
5.1
2
1
terrace
P/Mi
CRCPHI
10
1.67
5.0
0.54
8.1
8.2
2
1
terrace
P/Mi
CRCPHI
20
1.80
4.7
0.39
12.0
7.5
2
2
terrace
Ma/Mi/P
CRCPHI
10
1.68
4.9
0.44
6.1
5.6
2
2
terrace
Ma/Mi/P
CRCPHI
20
1.91
4.8
0.35
10.6
4.4
3
1
terrace
Mi/Mi
CCP
10
1.74
6.1
0.56
4.4
2.3
3
1
terrace
Mi/Mi
CCP
20
1.77
6.2
0.51
6.1
2.9
13.9375
-15.9622
13.9400
-15.9436
13.6969
-15.9055
13.9255
13.8761
13.8953
13.9478
-16.0408
-16.0189
-16.0208
-15.9311
Table 14: Porokhane data set
xxiv
LAND OBSERVATION AND LAND
MANAGEMENT SURVEY
xxv
Observation 1
Village : Djiguimar
Transect number: 1
Parcel number from the top : 1
Coordinates: 13º38’679”N 15º33’813”W
Position on the landscape : Plateau
Vegetation type: guieria senegalensis, combretum glutinosum, penisetum
achyde,’ndiangue’,’mboum ndour’.
Landowner: not cultivated, never cultivated because of the block of stones.
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR3/3
Sandy clay
many
termites
pedicelatum,
sparmaceae
20
7.5YR4/4
Clay
Few
Land management
Land use
Actual
Fallow
Previous
Fallow
2
fallow
xxvi
3
fallow
4
fallow
5
Fallow
6
fallow
Observation 2
Village : Djiguimar
Transect number : 1
Parcel number from the top : 2
Coordonnées spatiales : 13º38’740”N 15º33’780”W
Position on the landscape : glacis
Vegetation types : penisetum pedicelatum, Vitex doniana,’mboum ndour’.
Landowner : Ousmane Toure
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
7.5YR2/3
Clayey sand
Yes
Termites
20
10YR2/3
Clayey sand
Yes
Land management, cleared 45 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Sorghum
150 kg/ha
Previous
Peanut
no
2
Millet
100kg/ha
3
P
no
No
no
No
no
superficial
Removed
and burnt
superficial
removed
Superficial
Removed
and burnt
superficial
removed
xxvii
4
M
Less than
100 kg/ha
No
5
P
No
6
M
No
No
superficial
Removed
and burnt
superficial
Removed
superficial
Removed
and burnt
Observation 3
Village : Djiguimar
Transect number : 1
Parcel number from the top : 3
Coordonnées spatiales : 13º38’772”N 15º33’759”W
Position on the landscape : Glacis ( on the slope)
Vegetation types : Eragrostis tremula, ‘ndjangue’, ‘ndeti noor’, guieria senegalensis, Ziziphus amuritiana
Landowner : Alioune Coumba Toure
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
7.5YR2/2
Loamy sand
many
Termites and other
insects
20
10YR2/3
Loamy sand
Many fine
Land management, cleared approximately in 1960
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Sorghum
Previous
Peanut
100 kg/ha
2
Millet
150 kg/ha
3
Fallow
4
Peanut
5
Millet
6
Peanut
No
no
No
No
no
no
No
superficial
Removed
and burnt
superficial
removed
Superficial
Removed
and burnt
superficial
superficial
Removed
superficial
Removed
and burnt
superficial
Removed
xxviii
Observation 4
Village : Djiguimar
Transect number : 1
Parcel number from the top : 4
Coordonnées spatiales : 13º38’823”N 15º33’733”
Position on the landscape : Glacis
Vegetation types : Herbs: ‘ndeti noor’, Spermaceae achydea, ‘ndiangue’,
Shrubs: guieria senegalensis, Piliostigma reticulatum, Hibiscus asper
Trees : acacia albida, Cordyla pinnata.
Landowner :
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR2/3
Sand
fine
Termites,
worm
20
10YR3/3
Clayey sand
Fine
one
Land management, cleared in 1960
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
Low input
No
superficial
Remove and
burn
Previous
Peanut
Low or
input
No
no
superficial
Remove for
animal
feeding
2
Millet
Low input
No
Superficial
Remove and
burn
xxix
3
Peanut
Low or
input
no
no
superficial
Remove for
animal
feeding
4
Millet
Low input
No
Superficial
Remove and
burn
5
Peanut
Low or
input
no
no
superficial
Remove for
animal
feeding
6
Millet
Low input
no
Superficial
Remove and
burn
Observation 5
Village : Djiguimar
Transect number : 1
Parcel number from the top : 5
Coordonnées spatiales : 13º38’898”N 15º33’735”W
Position on the landscape : Teraces
Vegetation types : guieria senegalensis, Piliostigma reticulatum, Spermaceae achydea, Cassia siberiana,‘mboum
ndour’,
Landowner : cattle course never cultivated, always in fallow
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR2/2
Clayey sand
Yes
Lot of termites
20
10YR2/2
Sandy clay
Yes
30
10YR2/1
Sandy clay
Land management
Land use
Actual
Fallow
Previous
fallow
2
Fallow
xxx
3
fallow
4
Fallow
5
Fallow
6
fallow
Observation 6
Village: Djiguimar
Transect number: 1
Parcel number from the top: 6
Coordonnées spatiales: 13º38'983’’N 15º33'735’’W
Position on the landscape: Bas Fond’ (low ground)
Vegetation types: guieria senegalensis, penisetum pedicelatum, ‘ndjiangue’, Eragrostis tremula, ‘mboum ndour’.
Landowner: Katim Antia Toure
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR2/3
Clayey sand
Yes
Termites
20
5YR4/6
Sand
Yes
Land management, cleared approximately in 1955, not cultivated since 1984 because of
water flooding. This land is almost abandoned.
Land use
Actual
Fallow
Previous
fallow
2
fallow
3
fallow
xxxi
4
fallow
5
fallow
6
fallow
Observation 7
Village: Djiguimar
Transect number: 2
Parcel number from the top: 1
Coordonnées spatiales: 13º38’702”N 15º33’663”W
Position on the landscape: Glacis, just after the plateau starting the slope
Vegetation types: guieria senegalensis, Hibiscus asper, ‘ndeti noor’, Eragrostis tremula.
Landowner: Daouda Kani Toure
Depth (cm)
Color
Texture
Roots
10
10YR4/3
Sand
Yes
Activité
biologique
Termites
20
5YR4/4
Clay
No. stones
after 10 cm
Cuirass
just
Land management, cleared approximately in 1955
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Peanut
150 kg/ha
No
superficial
Removed
Previous
Millet
Low or no
imput
no
2
Peanut
Low or no
imput
No
3
Millet
Low or no
imput
no
4
Peanut
Low or no
imput
no
5
Millet
Low or no
imput
no
6
Peanut
Low or no
imput
no
superficial
Removed and
burnt
Superficial
Removed
superficial
Removed and
burnt
superficial
removed
superficial
Removed and
burnt
superficial
removed
xxxii
Observation 8
Village: Djiguimar
Transect number: 2
Parcel number from the top: 2
Coordinates: 13º38’739”N 15º33’634”
Position on the landscape : Glacis
Vegetation types : guieria senegalensis, Eragrostis tremula, ‘ndeti noor’, Hibiscus asper, Cordyla pinnata.
Landowner: Daouda Kani Toure
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR2/3
sand
yes
termites
20
10YR3/3
Clayey sand
Yes
No
Land management, cleared approximately in 1955
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Peanut
150 kg/ha
No
superficial
Removed
Previous
Millet
Low or no
imput
no
2
Peanut
Low or no
imput
No
3
Millet
Low or no
imput
no
4
Peanut
Low or no
imput
no
5
Millet
Low or no
imput
no
6
Peanut
Low or no
imput
no
superficial
Removed
and burnt
Superficial
Removed
superficial
Removed
and burnt
superficial
removed
superficial
Removed
and burnt
superficial
removed
xxxiii
Observation 9
Village: Djiguimar
Transect number: 2
Parcel number from the top: 3
Coordinates: 13º38’803”N 15º33’637”
Position on the landscape: Glacis
Vegetation types: guieria senegalensis, ‘fouf’, Spermaceae achydea, Eragrostis tremula, penisetum pedicelatum.
Landowner: Mor Coumba Toure
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
7.5YR2/3
Clay sand
Yes
Termites
20
7.5YR3/3
Sandy clay
Yes
Land management, cleared approximately in 1943
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Sorghum
Low or no
input
No
Previous
peanut
Low or no
input
No
2
Millet
Low or no
input
No
3
peanut
Low or no
input
no
4
millet
Low or no
input
no
5
peanut
Low or no
input
no
6
millet
Low or no
input
no
superficial
Removed and
burnt
superficial
removed
Superficial
Removed and
burnt
superficial
removed
superficial
Removed and
burnt
superficial
removed
superficial
Removed and
burnt
xxxiv
Observation 10
Village : Djiguimar
Transect number : 2
Parcel number from the top : 4
Coordinates : 13º38’839”N 15º33’631”
Position on the landscape : Glacis
Vegetation types : guieria senegalensis, , penisetum pedicelatum, ‘fouf’
Landowner : Mor Coumba Toure
Depth (cm)
Color
Texture
Roots
Activité
biologique
Other observation
10
5YR3/3
Loamy sand
Yes
Termites, ‘ndjalal’
20
5YR4/6
Loamy clay
Little
Water
crossing,
sign of erosion.
Land management
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Peanut
Low or no
input
No
Previous
Millet
Low or no
input
No
2
Peanut
Low or no
input
No
3
Millet
Low or no
input
no
4
Peanut
Low or no
input
no
5
Millet
Low or no
input
no
6
Peanut
Low or no
input
no
superficial
Removed
superficial
Removed and
burnt
Superficial
Removed
superficial
Removed and
burnt
superficial
removed
superficial
Removed and
burnt
superficial
removed
xxxv
Observation 11
Village : Djiguimar
Transect number : 2
Parcel number from the top : 5
Coordonnées spatiales : 13º38’938”N 15º33’602”
Position on the landscape : low ground
Vegetation types : ‘kirindol’, ‘wolo’, ‘baara(90%)’, ‘mboum ndour’, ‘dimb’ and others
Landowner : Dialigue Diallo
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR2/3
Loamy sand
Many
Termites and other
insects
20
10YR2/2
Clayey sand
Yes
Land management, cleared probably 40 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
No
Previous
millet
No
2
Millet
No
3
millet
no
4
millet
no
5
millet
no
6
millet
no
No
No
No
no
no
no
no
superficial
Removed and
burnt
superficial
Removed and
burnt
superficial
Removed and
burnt
superficial
Removed and
burnt
superficial
Removed and
burnt
superficial
Removed and
burnt
superficial
Removed and
burnt
Peanut has been cultivated in this parcel 7 years ago but the crop has been destroyed with
water flooding.
xxxvi
Observation 12
Village: Djiguimar
Transect number: 3
Parcel number: 1
Coordinates : 13º38’740” N 15º33’830”W
Position on the landscape: Glacis near the plateau
Vegetation types: ‘ndidji bopp’, ndiangue’, ‘mboum’, ngueria senegalensis, ‘rate’.
Landowner : Ousmane Toure
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR2/3
Loamy sand
Many
termites
20
10YR3/3
Clayey sand
Yes
Land management, cleared 45 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Fallow
No
Previous
Peanut
No
2
Millet
100kg/ha
3
P
no
No
No
No
no
No
Burnt
superficial
removed
superficial
Removed
and burnt
superficial
removed
xxxvii
4
M
Less than
100 kg/ha
no
5
P
No
6
M
No
No
superficial
Removed
and burnt
superficial
Removed
superficial
Removed
and burnt
Observation 13
Village : Djiguimar
Transect number : 3
Parcel number from the top : 2
Coordinates : 13º38’797” N 15º33’815”W
Position on the landscape : Glacis far away from the plateau
Vegetation types :
Landowner : Ousmane Toure
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
7.5YR3/4
Sandy
Yes
Termites
20
7.5YR3/2
Loamy sand
Yes
Land management, cleared 45 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
millet
No or
input
No
low
superficial
Removed, the
strongest
stalk,
the
remainings
burnt
Previous
Peanut
No or low
input
no
2
Millet
No or low
input
No
3
Peanut
No or low
input
no
4
Millet
No or low
input
no
5
Peanut
No or low
input
no
6
Millet
No or low
input
no
superficial
removed
superficial
Removed, the
strongest
stalk,
the
remainings
burnt
superficial
removed
superficial
Removed, the
strongest
stalk,
the
remainings
burnt
superficial
removed
superficial
Removed, the
strongest
stalk,
the
remainings
burnt
xxxviii
Observation 14
Village : Djiguimar
Transect number : 3
Parcel number from the top : 3
Coordonnées spatiales : 13º38’865”N 15º33’826”W
Position on the landscape : Glacis, near the terraces and water crossing
Vegetation types : ngueria senegalensis, ‘ndidji bop’, ‘ndiangue’.
Landowner : Dialigue Diallo
Depth (cm)
Color
Texture
Roots
Animal
10
7.5YR3/4
sand
yes
termites
20
7.5YR3/3
Clayey sand
Yes
Land management
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Sorghum
Low or no
input
No
Previous
Peanut
Low or no
input
no
2
Millet
Low or no
input
No
3
Peanut
Low or no
input
no
4
millet
Low or no
input
no
5
peanut
Low or no
input
no
6
Millet
Low or no
input
no
superficial
Removed, the
remaining
burnt
superficial
Removed for
livestock
feeding
superficial
Removed, the
remaining
burnt
superficial
Removed for
livestock
feeding
superficial
Removed, the
remaining
burnt
superficial
Removed for
livestock
feeding
superficial
Removed, the
remaining
burnt
xxxix
Observation 15
Village : Djiguimar
Transect number : 3
Parcel number from the top : 4
Coordonnées spatiales : 13º38’927”N 15º33’827”W
Position on the landscape : Teraces
Vegetation types : shrubs : ngueria senegalensis, ‘rate’, trees : ‘khekhou’, ‘yiir’.
Landowner : Papa Sacko Toure
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR2/3
sandy
yes
termites
20
10YR2/3
Loamy sand
Yes
Land management, cleared 80 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
Low or no
input
No
Previous
Peanut
Low or no
input
no
2
Fallow
Low or no
input
No
3
Millet
Low or no
input
no
4
Peanut
Low or no
input
no
5
Millet
Low or no
input
no
6
Peanut
Low or no
input
no
superficial
Removed,
remaining
burnt
superficial
Removed
superficial
Burnt
superficial
Removed,
remaining
burnt
superficial
Removed
superficial
Removed,
remaining
burnt
superficial
Removed
xl
Observation 16
Village : Djiguimar
Transect number : 3
Parcel number from the top : 5
Coordonnées spatiales : 13º39’063”N 15º33’881”W
Position on the landscape : low ground (Bas Fond)
Vegetation types : shrubs : ngueria senegalensis, ‘jujubier’, ‘poftane’, ‘kirindol’, trees : asodactiva indica (nim),
acacia albida (kad), ‘gung’, ‘solom’, ‘founokh’.
Landowner : Daouda Antia Toure
Depth (cm)
Color
Texture
Roots
Biological
activity
10
7.5YR3/2
Sand
many
termites
20
5YR4/4
Sand
Many
Land management, cleared in 1950 and rice is the first crop cultivated in this land in the
fifties.
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
millet
No
Previous
maize
no
2
Millet
No
3
maize
no
4
millet
no
5
maize
no
6
Millet
no
No
no
No
no
no
no
no
superficial
Removed for
fence
building, the
remaining
burnt
superficial
Removed for
animal
feeding
superficial
Removed for
fence
building, the
remaining
burnt
superficial
Removed for
animal
feeding
superficial
Removed for
fence
building, the
remaining
burnt
superficial
Removed for
animal
feeding
superficial
Removed for
fence
building, the
remaining
burnt
xli
Observation 17
Village : Paoskoto
Transect number : 1
Parcel number from the top : 1
Coordinates : 13º47’722”N 15º47’312”W
Position on the landscape : Plateau with may blocks
Vegetation types : ‘rate’, ngueria senegalensis, ‘khessaw’,’ tumb’.
Landowner : fallow never cultivated, because of the blocks of stones
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR4/3
sand
Fines
termites
20
7.5YR4/4
Clay
Yes
White worms
Land management
Land use
Actual
Fallow
Previous
fallow
2
Fallow
3
fallow
xlii
4
fallow
5
fallow
6
fallow
Observation 18
Village : Paoskoto
Transect number : 1
Parcel number from the top : 2
Coordonnées spatiales : 13º47’737”N 15º47’252”W
Position on the landscape : glacis
Vegetation types : ‘rate’, ngueria senegalensis, ‘khessaw’,’ tumb’, ‘sam’.
Landowner : Malick Drame
Depth (cm)
Munsell color
Texture
Roots
Biological Activity
10
10YR3/4
Loamy sand
Yes
Termites
20
7.5YR 4/4
Loamy clay
Yes
Land management, since 1960 rotation millet-peanut except when seeds are not available
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
fallow
Burnt
Previous
Peanut
no
2
Millet
No
3
Peanut
no
4
Millet
no
5
Peanut
no
6
Millet
No
No
No
no
no
no
no
No
removed
Burnt
removed
burnt
removed
burnt
xliii
Observation 19
Village : Paoskoto
Transect number : 1
Parcel number from the top : 3
Coordinates : 13º47’740”N 15º47’198”W
Position on the landscape : glacis
Vegetation types : ngueria senegalensis, ‘rate’, ‘fouf’.
Landowner : Malick Drame
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR3/3
Loamy
Yes
termites
20
7.5YR4/4
Clayey Loam
Yes
Land management, rotation millet-peanut since 1960
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
No
Previous
Peanut
No
2
Millet
no
3
Peanut
no
4
Millet
no
5
Peanut
no
6
Millet
no
No
No
no
no
no
no
no
With
hoe
sine
Removed
and burnt on
the land
With hoe
sine
Removed
With hoe
sine
Removed
and burnt on
the land
With hoe
sine
Removed
With hoe
sine
Removed
and burnt on
the land
With hoe
sine
Removed
With hoe
sine
Removed
and burnt on
the land
xliv
Observation 20
Village : Paoskoto
Transect number : 1
Parcel number from the top : 4
Coordinates : 13º47’744”N 15º47’130”W
Position on the landscape : glacis
Vegetation types : ‘rate’, ‘dimb’.
Landowner : Kabe Deme
Depth (cm)
Color
Texture
Roots
Biological
activity
10
7.5YR2/2
Loamy
Many
termites
20
7.5YR4/4
Clayey loam
Few
Land management, cleared 44 years ago, rotation peanut-maize which could be shifted
by a fallow in case of seed unavailability.
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Maize
no
Previous
Peanut
No
2
Maize
No
3
Peanut
no
4
Maize
no
5
Peanut
no
6
Maize
No
no
No
No
no
no
no
no
With
hoe
sine
Removed
and burn the
remainings
With hoe sine
With hoe
sine
Removed
and burn
the
remainings
With hoe
sine
Removed
With hoe
sine
Removed
and
burn
the
remainings
With hoe
sine
Removed
With hoe
sine
Removed
and
burn
the
remainings
Removed
xlv
Observation 21
Village : Paoskoto
Transect number : 1
Parcel number from the top : 5
Coordinates : 13º47’762”N 15º47’045”W
Position on the landscape : glacis
Vegetation types : ‘ndjangue’, ‘bissap’, ‘baara’.
Landowner : Elhaji Deme
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR3/4
Loam sand
Few
termites
20
7.5YR4/6
Clayey loam
No
Land management, cleared 60 years ago, rotation millet-peanut
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Peanut
No
Previous
Millet
no
2
Peanut
No
3
Millet
no
4
Peanut
no
5
Millet
no
6
Peanut
no
No
no
No
no
no
no
no
With
hoe
sine
Removed
and burn the
remainings
With hoe sine
With hoe
sine
Removed
and burn
the
remainings
With hoe
sine
Removed
With hoe
sine
Removed
and
burn
the
remainings
With hoe
sine
Removed
With hoe
sine
Removed
and
burn
the
remainings
Removed
xlvi
Observation 22
Village : Paoskoto
Transect number : 1
Parcel number from the top : 6
Coordinates : 13º47’768”N 15º46’997”W
Position on the landscape : teraces
Vegetation types : ‘rate’, ‘nguiguis’, ‘bissap’.
Landowner : Elhadji Dem
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
7.5YR4/3
Loam sand
many
termites
20
7.5YR4/6
Loam clay
Few
Land management, same as previous parcel except for the actual season where maize has
been cultivated.
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Maize
no
Previous
Millet
no
2
Peanut
No
3
Millet
no
4
Peanut
no
5
Millet
No
6
Peanut
no
no
no
No
no
no
No
no
With
hoe
sine
Removed
and burnt the
remainings
With hoe sine
With hoe
sine
Removed
With hoe
sine
Removed
and burnt
the
remaining
With hoe
sine
Removed
With hoe
sine
Removed
and burnt
the
remaining
With hoe
sine
Removed
Removed and
burnt
the
remainings
xlvii
Observation 23
Village : Paoskoto
Transect number : 1
Parcel number from the top : 7
Coordonnées spatiales : 13º47’776”N 15º46’911”W
Position on the landscape : teraces
Vegetation types : shrub and grass burnt during our visit, trees : ‘ronier’, ‘dimb’
Landowner : Matar Mane
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR3/3
Loamy sand
Many
termites
20
7.5YR4/4
Loam clay
Few
Land management,
Cleared more than 60 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop residues
Actual
Water melon
Previous
Peanut
Low input
Low input
2
Water
melon
Low input
No
No
No
Low
input
No
Hoe
and
tractor
removed
Hoe and
tractor
Burnt
Hoe and
tractor
removed
Hoe and
tractor
Burnt
xlviii
3
Peanut
4
Water
melon
Low input
5
Peanut
Low input
6
Water
melon
Low input
No
No
No
Hoe and
tractor
removed
Hoe and
tractor
Burnt
Hoe and
tractor
removed
Observation 24
Village : Paoskoto
Transect number : 1
Parcel number from the top : 8
Coordinates : 13º47’708”N 15º46’813”W
Position on the landscape : teraces
Vegetation types : ‘ndatoukane’, ‘baara’ (very few),’rate’, ‘ dimb’ (1)
Landowner : Abdou Niass
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR2/3
Clayey sand
Many, long
sharp
Termites
and
20
7.5YR4/3
Sandy clay
Sharp
Land management
Cleared more than 60 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Sorghum
Yes but low
Previous
Maize
Yes but low
2
Sorghum
Yes but low
3
Maize
Yes but low
4
Sorghum
Yes but low
5
Maize
Yes but low
6
Sorghum
Yes but low
No
No
No
No
No
No
No
Hoe/tractor
Removed for
fence building
Hoe/tractor
Removed for
cattle feeding
Hoe/tractor
Removed for
fence building
Hoe/tractor
Removed for
cattle feeding
Hoe/tractor
Removed for
fence building
Hoe/tractor
Removed for
cattle feeding
Hoe/tractor
Removed for
fence building
xlix
Observation 25
Village : Paoskoto
Transect number : 1
Parcel number from the top : 9
Coordinates : 13º47’909”N 15º46’546”W
Position on the landscape : teraces (near the low ground)
Vegetation types : tree : dimb, no grass, no shrub (cattle enclosing)
Landowner : Ahmadou Ba
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR3/2
Clayey sand
Yes
termites
20
10YR3/4
Clay
Yes
Land management, cleared more than 60 years, cattle enclosing at least 20 years
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
No
Previous
Millet
No
2
Millet
No
3
Millet
No
4
Millet
No
5
Millet
No
6
Millet
No
Cattle
enclosing
Hoe sine
Burnt
Cattle
enclosing
Hoe sine
Burnt
Cattle
enclosing
Hoe sine
Burnt
Cattle
enclosing
Hoe sine
Burnt
Cattle
enclosing
Hoe sine
Burnt
Cattle
enclosing
Hoe sine
Burnt
Cattle
enclosing
Hoe sine
Burnt
l
Observation 26
Village : Paoskoto
Transect number : 1
Parcel number from the top : 10
Coordinates : 13º47’895”N 15º46’339”W
Position on the landscape : Low ground
Vegetation types : grass : ‘ndiangue’(100%), ‘wass wassou’, ‘ndattoukane’, shrubs : ‘tumb’, ‘rate’, ‘mboum
ndour’, ‘bissap’, trees: acacia sahel, ‘dimb’.
Landowner : Not cultivated because of water flooding during rainy season
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR3/2
Sandy loam
Many, sharp
termites
20
10YR3/2
Clayey loam
Few, sharp
30
10YR4/2
Clayey loam
yes
40
10YR4/2
Sandy clay
Yes
Land management
Land use
Actual
fallow
Previous
fallow
2
fallow
3
fallow
li
4
fallow
5
fallow
6
fallow
Observation 27
Village : Paoskoto
Transect number : 2
Parcel number from the top : 1
Coordinates : 13º47’860”N 15º47’622”W
Position on the landscape : Plateau without any block
Vegetation types : shrub : ‘bissap sauvage’(70%), ‘mboum ndour’ (40%) grass :
‘ndiangue’(70%),
Landowner : Sama Thiam
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
7.5YR3/4
Loamy sand
Yes
termites
‘baara’ (50%),
20
5YR4/4
Clayey sand
Yes
Land management, cleared 80 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Maize
yes
Previous
Millet
No
2
Maize
yes
3
Millet
no
4
Maize
yes
5
Millet
no
6
Maize
Yes
Yes but little
Yes but little
Hoe sine
Removed for
cattle feeding
Hoe sine
Burn
remainings
after
removing the
strongest
stalk
Yes but
little
Hoe sine
Removed
for cattle
feeding
Yes but
little
Hoe sine
Burn
remainings
after
removing
the
strongest
stalk
Yes but
little
Hoe sine
Removed
for cattle
feeding
Yes but
little
Hoe sine
Burn
remainings
after
removing
the
strongest
stalk
Yes but
little
Hoe sine
Removed
for cattle
feeding
lii
Observation 28
Village : Paoskoto
Transect number : 2
Parcel number from the top : 2
Coordinates : 13º47’917”N 15º47’602”W
Position on the landscape : glacis
Vegetation types : grass : ‘salgouf’, ‘baara’, ‘ndatoukane’, shrubs: ‘ngueria senegalensis’, ‘rate’.
Landowner : Aladji Mane
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
7.5YR3/3
Sandy
Yes
termites
20
7.5YR4/4
Sandy clay
Yes
Land management, cleared more than 45 years
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet and
Water melon
Previous
Peanut
Enough
input (250
kg )
yes
Enough input
Hoe
tractor
Burnt
and
2
Millet and
Water
melon
Enough
input
3
Peanut
5
Peanut
Enough
input
4
Millet and
Water
melon
Enough
input
Enough
input
6
Millet and
Water
melon
Enough
input
Yes
yes
yes
yes
yes
yes
Hoe and
tractor
Removed
Hoe and
tractor
Burnt
Hoe and
tractor
Removed
Hoe and
tractor
Burnt
Hoe and
tractor
Removed
Hoe and
tractor
Burnt
liii
Observation 29
Village : Paoskoto
Transect number : 2
Parcel number from the top : 3
Coordinates : 13º47’982”N 15º47’557”
Position on the landscape : glacis
Vegetation types : grass : ‘baara’ tree : ‘dimb’ (parcel completely burnt)
Landowner : Keba Khouredia Mane
Depth (cm)
Color
Texture
Roots
Biological
activity
10
7.5 YR3/3
20
7.5YR4/4
Many
termites
Few
Land management, cleared 100 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
Yes
Previous
Peanut
No
2
Millet
Yes
3
Peanut
No
4
Millet
Yes
5
Peanut
No
6
Millet
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Hoe/tractor
Burnt
Hoe/tractor
Removed
Hoe/tractor
Burnt
Hoe/tractor
Removed
Hoe/tractor
Burnt
Hoe/tractor
Removed
Hoe/tractor
Burnt
liv
Observation 30
Village : Paoskoto
Transect number : 2
Parcel number from the top : 4
Coordinates : 13º48’041”N 15º47’542”
Position on the landscape : glacis
Vegetation types : grass : ‘baara’, ‘salgouf’, ‘ndiangue’, shrubs : ‘rate’, ‘nguiguis’, ngueria senegalensis, ‘tumb’,
trees : ‘dimb’
Landowner : Mamouth Mane
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
7.5YR3/3
20
7.5YR4/4
Yes
Termites
Yes
Land management, cleared approximately 50 years ago
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop residues
Actual
Maize
Yes
Previous
Millet
Yes
2
Maize
Yes
3
Millet
Yes
4
Maize
Yes
5
Millet
Yes
6
Maize
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Hoe sine
Hoe sine
Hoe sine
Hoe sine
Hoe sine
Hoe sine
Burnt
Burnt
Burnt
Hoe
sine
Burnt
Burnt
Burnt
Burnt
lv
Observation 31
Village : Paoskoto
Transect number : 2
Parcel number from the top : 5
Coordinates : 13º48’122”N 15º47’502”W
Position on the landscape : teraces
Vegetation types : grass : ‘baara’, ‘salgouf’. shrubs : ‘rate’, ngueria senegalensis, trees : ‘garabou laobe’, ‘dimb’.
Landowner : Cheikhou Mane
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
7.5YR3/3
20
7.5YR4/4
Yes
termites
Yes
Land management, cleared more than 45 years
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
millet
No
Previous
Peanut
No
2
millet
No
3
Peanut
No
4
Millet
No
5
Peanut
No
6
millet
No
No
No
No
No
No
No
No
No
Burnt
No
Removed
No
Burnt
No
Removed
No
Burnt
No
Removed
No
Burnt
lvi
Observation 32
Village : Paoskoto
Transect number : 2
Parcel number from the top : 6
Coordinates : 13º48’195”N 15º47’455”
Position on the landscape : Low ground (Bas fond)
Vegetation types : grass : ‘ndiangue’ (100%), shrub : ‘mboum ndour’, (90%), trees : ‘soto’, ‘dimb’.
Landowner : Moussa Sarr
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
7.5YR3/2
20
7.5YR2/3
30
40
Many
Termites
many
few
Very few
Land management, cleared more than 45 years ago, mineral fertiliser once every 4 years
and never organic fertiliser
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
sorgho
Yes
Previous
Peanut
2
Millet
3
Peanut
4
Millet
5
Peanut
6
Millet
No
No
No
Yes
No
No
No
No
No
No
No
No
No
Hoe + tractor
Hoe + tractor
Burnt
Removed
Hoe +
tractor
Burnt
Hoe +
tractor
Removed
Hoe +
tractor
Burnt
Hoe +
tractor
Removed
Hoe +
tractor
Burnt
and
lvii
Observation 33
Village: Prokhane
Transect number: 1
Parcel number: 1
Coordinates: 13º40’957”N 15º51’580”W
Position on the landscape: plateau
Vegetation types: vegetation completely burnt, trees : no trees in the parcel but enclosed with ‘nim’ and ‘dimb’.
Landowner : Serigne Moustapha Bassirou Mbacke, managed by El hadji Ndiaye
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
7.5 YR5/6
Sandy
Many
Termites
20
7.5YR4/4
Clay
many
Land management, intensification started in 1968
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Maize
150 kg/ha
15-10-10
150 kg/ha
urea
Previous
Millet
150
kg/ha
15-10-10
2
Peanut
150 kg/ha 620-10
4
Millet
150 kg/ha
15-10-10
5
Peanut
150 kg/ha
6-20-10
6
Maize
150 kg/ha
15-10-10
150 kg/ha
urea
No
3
Maize
150
kg/ha 1510-10
150
kg/ha
urea
No
No
No
No
No
No
Tractor and
hoe
Burnt
Tractor and
hoe
Burnt
Tractor and
hoe
Removed
Tractor
and hoe
Burnt
Tractor and
hoe
Burnt
Tractor and
hoe
Removed
Tractor and
hoe
Burnt
lviii
Observation 34
Village: Prokhane
Transect number: 1
Parcel number: 2
Coordinates: 13º40’657”N 15º51’404”W
Position on the landscape: plateau (depression part)
Vegetation types : ‘ndeti noor’, ‘ndatoukane’, ‘bissap sauvage’, ‘roukh’, ‘salgouf’, enclosed with trees, ‘nim’
and’ dimb’.
Landowner : Serigne Moustapha Bassirou
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR2/3
Sandy clay
Yes
Termites
20
10YR2/3
Clay
Yes
Land management, intensification started in 1968
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop residues
Actual
Rice
150
kg/ha
15-10-10
150
kg/ha
urea
Previous
Millet
150 kg/ha 1510-10
2
Peanut
150 kg/ha
6-20-10
4
Millet
150 kg/ha
15-10-10
5
Peanut
150 kg/ha
6-20-10
6
Maize
150 kg/ha
15-10-10
150 kg/ha
urea
No
3
Maize
150
kg/ha
15-1010
150
kg/ha
urea
No
No
No
No
No
No
Hoe
and
tractor
Not removed
yet but will
be burnt
No
No
No
No
No
No
Burnt
Removed
Burnt
Burnt
Removed
Burnt
lix
Observation 35
Village: Prokhane
Transect number: 1
Parcel number: 3
Coordinates: 13º40’984”N 15º51’337”W
Position on the landscape: plateau
Vegetation types: crop residues, shrubs and grass completely burnt. Some remaining ‘bissap sauvage’
Landowner : Serigne Moustapha Bassirou
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR3/3
Sandy clay
Yes
Termites
20
10YR4/4
Clay
Yes
Land management, intensification started in 1968
Actual
Maize
150
kg/ha
15-10-10
150
kg/ha
urea
Previous
Millet
150 kg/ha 1510-10
2
Peanut
150 kg/ha
6-20-10
Organic
Fertiliser
Tillage
No
No
No
Tractor and
hoe
Tractor and
hoe
Crop residues
Burnt
Burnt
Removed
Land use
Mineral
fertiliser
Tractor
hoe
and
lx
3
Maize
150
kg/ha
15-1010
150
kg/ha
urea
No
4
Millet
150 kg/ha
15-10-10
5
Peanut
150 kg/ha
6-20-10
6
Maize
150 kg/ha
15-10-10
150 kg/ha
urea
No
No
No
Tractor
and
hoe
Burnt
Tractor and
hoe
Tractor and
hoe
Tractor and
hoe
Burnt
Removed
Burnt
Observation 36
Village : Prokhane
Transect number : 1
Parcel number : 4
Coordinates : 13º41’049”N 15º51'200’’W
Position on the landscape : plateau
Vegetation types : shrubs : ‘ngueria senegalensis’, grass : ‘ndiangue’, ‘ndatoukane’, ‘ndeti noor’, ‘roukh’.
Landowner :
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR3/3
Sandy clay
Yes
Termites
20
7.5YR4/3
Clay
Yes
Land management, not intensified since at least 10 years
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop residues
Actual
Peanut
No
Previous
Millet
No
2
Peanut
No
3
Millet
No
4
Peanut
No
5
Millet
No
6
Peanut
No
No
No
No
No
No
No
No
Hoe
Removed
Hoe
Burnt
Hoe
Removed
Hoe
Burnt
Hoe
Removed
Hoe
Burnt
Hoe
Removed
lxi
Observation 37
Village : Prokhane
Transect number : 1
Parcel number : 5
Coordinates : 13º40’932”N 15º51’687”W
Position on the landscape : plateau
Vegetation types : shrubs : ngueria senegalensis, acacia albida, grass : ‘baara’‘ndeti noor’, ‘fouf’.
Landowner : Iman of the village
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
7.5YR2/3
Sandy clay
Yes
termites
20
7.5YR4/4
Clay
Yes
Land management, not intensified since at least 10 years
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
No
Previous
Peanut
No
2
Millet
No
3
Peanut
No
4
Millet
No
5
Peanut
No
6
Millet
No
No
No
No
No
No
No
No
Hoe
Burnt
hoe
Removed
hoe
Burnt
hoe
Removed
Hoe
Burnt
hoe
Removed
hoe
Burnt
lxii
Observation 38
Village : Prokhane
Transect number : 2
Parcel number : 1
Coordinates : 13º40’754”N 15º51’608”W
Position on the landscape : plateau
Vegetation types : shrub : ‘bissap sauvage’, grass : ‘baara’, ndidji bopp’, ‘ndeti noor’.
Landowner : Serigne Mountakha
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR3/2
Clayey sand
Yes
Termites
20
Yes
Land management, intensification started in 1968 but since 10 years intensification in
term of mineral fertilizer input and of fossil energy has largely decreased but since then
organic fertiiser is used
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Peanut
No
Previous
Millet
100 kg/ha
2
Peanut
no
No
15 carts in
the 4ha
no
Tractor and
hoe
Removed
Tractor and
hoe
Burnt
Tractor
and hoe
Removed
lxiii
3
Millet
100
kg/ha
15 carts
in
the
4ha
Tractor
and hoe
Burnt
4
Peanut
No
5
Millet
100 kg/ha
6
Peanut
No
No
15 carts in
the 4ha
No
Tractor and
hoe
Removed
Tractor and
hoe
Burnt
Tractor and
hoe
Removed
Observation 39
Village : Prokhane
Transect number : 2
Parcel number : 2
Coordinates : 13º40’823”N 15º51'615”W
Position on the landscape : Plateau
Vegetation types : shrubs: ngueria senegalensis, ‘rate’, ‘nguiguis’, acacia albida, grass: ‘baara’, ndidji bopp’,
‘ndeti noor’.
Landowner : Serigne Moustapha Bassirou
Depth (cm)
Color
Texture
Roots
Biological
Activity
10
10YR3/3
Clayey sand
Yes
Termites
20
10YR3/4
Clay
Yes
Land management, this land is part of the previous parcel of Serigne Bassirou Mbacke
and the management is the same. The rotation is millet/maize/peanut
Actual
Millet
150
kg/ha
15-10-10
Previous
Peanut
150 kg/ha 620-10
2
Maize
150
kg/ha
15-10-10
150
kg/ha
urea
3
millet
150
kg/ha
15-1010
4
Peanut
150 kg/ha 620-10
5
Maize
150 kg/ha
15-10-10
150 kg/ha
urea
6
millet
150 kg/ha
15-10-10
Organic
Fertiliser
Tillage
No
No
no
no
No
no
no
Hoe and
tractor
Hoe and
tractor
Hoe and
tractor
Hoe and
tractor
Hoe and
tractor
Crop residues
Butrnt
Removed
Burnt
Hoe
and
tractor
Butrnt
Removed
Burnt
Butrnt
Land use
Mineral
fertiliser
Hoe
tractor
and
lxiv
Observation 40
Village : Prokhane
Transect number : 3
Parcel number : 1
Coordinates : 13º41’952”N 15º50'352”W
Position on the landscape : glacis
Vegetation types : shrubs : ‘nguiguis’, ‘mbankha’, ngueria senegalensis, grass : ‘baara’ (60%), ‘ndeti noor’
trees : ‘nguiguis, ‘soto’, ‘nim’, ‘gang’
Landowner : Mamadou Diao
Depth (cm)
Color
Texture
Roots
Activité
biologique
10
10YR2/2
Sandy
Yes
White
termites
20
10YR2/3
Clayey sand
Yes
warms,
Land management, this parcel has more than 100 years hold and is near the village (500
m). The village has moved 50 years ago from its original location and was closer to it
more than it is now. This parcel is used to benefit to the organic materal from household
waste. Since a long time this parcel is the cattle parking but the number of cows
decreased from more than to 100 units 10 years ago to less than 20 units.
Land use
Mineral
fertiliser
Organic
Fertiliser
Tillage
Crop
residues
Actual
Millet
No
Previous
Millet
No
2
Millet
No
3
Millet
No
4
Peanut
No
5
Millet
No
6
Millet
No
Cattle
parking
Hoe
Burnt
Cattle
parking
Hoe
Burnt
Cattle
parking
Hoe
Burnt
Cattle
parking
Hoe
Burnt
Cattle
parking
Hoe
Removed
Cattle
parking
Hoe
Burnt
Cattle
parking
Hoe
Burnt
lxv
GRAPHS
lxvi
6
5
Carbon
4
log C+S
3
BD
2
PH
1
0
Plateau
Glacis
Terrace
Bas fond
% carbon content
Figure 20: clay + silt, bulk density pH and carbon along the landscape (upper 20 cm).
1
0.8
0.6
Carbon
0.4
0.2
0
Plateau
Glacis
Terrace Bas fond
Position in the landscape
% Carbon (20cm)
Figure 21: distribution of carbon in average along the landscape
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0.66
0.58
0.40
0.39
Plateau
Glacis
Terrace
Bas fond
Position
Figure 22: Carbon distribution in a short (602 m) sloping landscape (5 %).
lxvii
% carbon (20 cm)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.15
0.56
0.4
0.35
Plateau
Glacis
Terrace
Bas fond
Position
% carbon (20 cm)
Figure 23: carbon distribution in a long (1810 m) gentle slope (< 1%)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0.34
0.32
Plateau
Glacis
0.49
0.44
Terrace
Bas fond
Position
Figure 24: carbon distribution in a short (685 m) gentle slope (< 1%)
1.4
1
0.8
top soil
0.6
sub soil
0.4
0.2
PF
T
PF
P
PF
BF
PL
I
R
C
C
R
C
C
PH
P
C
C
C
BF
I
0
C
% carbon
1.2
land use
lxviii
Figure 25: distribution of carbon in different types of land use
lxix
METEOROLOGICAL DATA
lxx
Table 15: Rainfall data in the Nioro area from 1950 to 2001 (Meteorology centre CNRA de Bambey,
Senegal)
1950
1951
1953
1954
1955
1956
1957
1958
1959
1961
1962
1963
1964
1965
1966
1967
1968
1969
Jan
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Feb
0
0
0
13
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Mar
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Apr
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
May
4
22
0
0
53
0
0
0
4
0
0
0
0
0
0
0
0
0
Jun
129
115
45
75
135
62
75
87
76
40
81
0
79
155
129
63
44
17
Jul
170
245
233
175
209
128
155
135
125
313
77
253
237
128
70
236
186
371
Aug
575
266
327
575
398
351
135
638
332
173
317
171
368
217
212
330
140
302
Sep
280
264
303
163
256
189
184
195
121
158
67
152
181
216
343
300
44
272
Oct
148
132
126
62
48
58
161
42
12
0
48
91
7
45
159
22
0
49
Nov
8
31
0
0
0
0
0
1
0
0
9
0
0
3
0
0
0
0
Dec
0
0
0
0
0
5
0
0
0
0
0
0
0
0
0
0
0
0
1315
1074
1035
1064
1099
792
710
1099
670
684
598
667
871
764
913
951
415
1010
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
Jan
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Feb
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Mar
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
Apr
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
May
0
0
0
0
0
0
15
1
0
10
0
9
0
8
0
1
1
0
Tot
Jun
37
37
80
81
20
2
54
18
77
160
13
32
7
65
211
34
27
100
Jul
136
177
49
126
130
260
233
65
192
281
84
233
149
140
56
170
87
140
Aug
262
297
194
219
263
247
158
163
255
209
217
272
221
73
186
153
339
334
Sep
125
208
145
136
190
341
197
247
156
90
182
174
103
110
164
133
298
209
Oct
32
19
25
15
26
53
100
22
24
15
25
67
62
22
14
25
49
117
Nov
0
0
0
0
0
0
0
0
55
0
0
0
0
0
0
19
0
0
Dec
0
0
0
0
0
0
4
0
0
6
3
0
0
0
0
0
0
0
593
738
494
577
629
902
761
515
757
770
523
786
542
418
632
536
801
900
Tot
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
Jan
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Feb
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Mar
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Apr
0
0
0
0
0
0
0
0
0
0
0
0
0
0
May
5
0
0
0
31
0
0
39
0
9
0
1
0
0
Jun
37
254
27
0
58
45
38
204
18
107
25
83
70
149
Jul
263
300
114
145
125
267
201
248
198
72
124
245
226
217
Aug
408
298
269
132
284
271
295
142
156
228
257
382
247
237
Sep
184
113
68
190
203
90
152
39
117
193
149
177
266
165
Oct
19
140
77
45
51
89
62
0
25
9
28
89
160
24
Nov
0
0
0
0
0
0
50
0
0
0
0
0
0
0
Dec
0
0
0
0
0
0
0
0
0
0
0
0
0
0
lxxi
Tot
915
1105
555
512
752
762
798
672
512
617
582
977
970
792
Table 16: Mean annual maximum and mean annual minimum temperature in the Nioro area (Meteorology
centre CNRA de Bambey, Senegal)
1985
1986
1988
1989
1990
1992
1993
1994
1996
1997
1998
1999
2000
Max mean temp
35
35
36
35
36
35
36
35
37
36
36
35
36
Min mean temp
21
20
20
20
21
21
21
20
21
22
22
21
20
lxxii
PICTURES
lxxiii
lxxiv