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COUNCIL FOR SCIENTIFIC AND INDUSTRIAL RESEARCH (CSIR)
SAVANNA AGRICULTURAL RESEARCH INSTITUTE (SARI)
WA STATION
P. O. Box 494, Wa, Ghana
Report on soil physical and chemical properties for soybean production in Upper West
Region of Ghana
By:
S.S. Buah and Godwin Opoku
September
2013
ii
Table of Contents
List of Tables ................................................................................................................................. iii
List of Figures ................................................................................................................................ iii
Executive summary ......................................................................................................................... 1
1.0 INTRODUCTION ............................................................................................................... 2
1.1 Background Information .................................................................................................. 2
1.2 Objectives ......................................................................................................................... 6
1.3 Methodology .................................................................................................................... 7
2.0 RESULTS OF THE STUDY ............................................................................................... 7
2.1 Soils of the Upper West Region ........................................................................................7
2.2 Assessment of the observed sites for crop (maize) production ........................................ 8
2.3 Soil chemical properties ................................................................................................. 10
3.0 CONCLUSIONS AND RECOMMENDATION .............................................................. 15
References ..................................................................................................................................... 18
Appendix 1 .................................................................................................................................... 19
Appendix 2....... ............................................................................................................................. 20
Appendix 3 .................................................................................................................................... 21
iii
List of Tables
Table 1: Project Sites - Districts and communities……………………………………………….3
List of Figures
Figure 1: Agro-Ecological Zones of Ghana and the distribution of the Project Sites .................... 5
Figure 2: Annual Rainfall distribution in Ghana ............................................................................ 6
Figure 3: Clay content of the selected district .............................................................................. 10
Figure 4: Top soil pH for the various sites ................................................................................... 11
Figure 5: Organic matter content for the various districts ............................................................. 13
Figure 6: Total N content for the various districts ........................................................................ 13
Figure 7: Available phosphorus for the various districts ............................................................... 14
Figure 8: Exchangeable potassium for the various districts ......................................................... 15
1
Executive Summary
Mennonite Economic Development Associates (MEDA) is a Non-Governmental Organization
(NGO) implementing the “Greater Rural Opportunities for Women (GROW)” Project in
northern Ghana comprising the Upper West (UWR), Upper East (UER) and Northern Regions
(NR). The MEDA’s GROW project aims to improve food security for 20,000 families in
northern Ghana by helping women increase availability, access and utilization of a variety of
appropriate and nutritious food through strengthening production and market linkages, increasing
diversification in production and creating nutrition awareness as well as fostering women’s
empowerment.
In an attempt to promote and increase soybean production among women in the UWR, MEDA
contracted the CSIR-SARI, Wa Station to assess soil properties for the production of soybean in
selected districts and communities in the region. This preliminary soil study covers selected
GROW project communities in five districts (Wa West, Wa East, Nadowli, Lambussie/Karni and
Sissala West districts). Soils were examined, described and sampled for laboratory analysis at 16
selected project sites comprising three each from four districts (Wa East, Nadowli,
Lambussie/Karni and Sissala West) and four from Wa West district. In general, the soils in all
the districts are suitable for the production of soybean even though most of the communities
have marginal soils. On the whole, soils in the region have a sandy texture, low nutrient contents
and consequently a low moisture retention capacity. In most of the communities, the major
limitations are:
2
1. Shallow soil depth and sandy soil textures with 56% of the sites having less than 6% clay
in the particle size analysis, making the soils prone to erosion and having low moisture
holding capacity
2. Soil fertility is generally low. The levels of organic matter, total nitrogen and available
phosphorus are generally very low. The low organic carbon and total N contents may be
attributed to the low biomass production and a high rate of decomposition.
3. Potassium is mostly abundant in the soils of northern Ghana, including UWR.
Obviously, there is an urgent need to prevent erosion and improve on soil fertility in the region.
Therefore, conscious effort must be made to build up organic matter and integrated soil fertility
management is absolutely necessary. Farmers in the various communities need to explore
strategies of making organic materials available since these are normally scarce in the savanna
agro-ecological systems. Such strategies will include integrated soil fertility management
practices such as combined use of organic and mineral fertilizers, use of quality seed of
improved crop varieties, appropriate crop associations (intercropping and crop rotations) and
crop residue retention. The inclusion of soybean in the cropping systems in the region may help
improve soil fertility and reduce Striga hermonthica incidence in Striga endemic areas.
1.0 INTRODUCTION
1.1 Background Information
In 2012 MEDA launched the Greater Rural Opportunities for Women (GROW) project to
improve food security for 20,000 families in northern Ghana by helping women increase
availability, access and utilization of a variety of appropriate and nutritious food through
strengthening production and market linkages, increasing diversification in production and
3
creating nutrition awareness. Using market based approaches the project will focus on three areas
to accomplish its goal. In addition, the project will assist women farmers to increase and
diversify farm production resulting in more food available to the family throughout the year. The
project will also help women sell their products – particularly soybeans – to high value markets
so that they can have increased income to buy food needed to supplement what they produce.
The GROW project is being implemented in 51 selected communities in five districts (Wa West,
Wa East, Nadowli, Lambussie/Karni and Sissala West) in the UWR but soils in only 16
communities were characterized (Table 1). This report covers soil characterization and mapping
of the 16 selected project sites in the region. The main objective of the soil analyses was to
assess the soil characteristics of the project sites for the production of soybean. Soil assessment
for crop production is normally done in the context of the crop’s requirement for growth. In
general, a crop growth requirement is not only restricted to soil but also other physical features
as climate, relief and vegetation are important.
Table 2: Project Sites - Districts and communities
District Communities
A B C D
Wa West Wechiau Poyentagnga Vieri Chogsie
Wa East Bulenga Loggu Goripie
Nadowli Kojokperi Yaruu Pulbaa
Lambussie/Karni Samoa Lambussie Naawie
Sissala West Nyamati Sorbelle Jeffesi
The UWR is located in the Guinea Savanna ecological zone (Fig. 1). This ecological zone is a
semi-arid region, characterized by low, erratic, and poorly distributed monomodal rainfall,
averaging about 1100 mm per annum. The annual rainfall increases from north to south. This is
4
characterized by distinct wet and dry seasons. Most of the rain in the area comes as short
duration high intensity storms between May and October. The peak of the rains is in August and
September. A long dry season is experienced from November/December to March/April, with
January and February being the driest months. An increasingly erratic rainfall pattern is without
doubt the most limiting factor to crop production in the region. Mean monthly temperatures are
high throughout the year ranging between 25 and 31O C.
Majority of the farmers in the UWR are engaged in subsistence food production. The principal
cereals grown in the region are maize (Zea mays) sorghum [Sorghum bicolor (L.) Moenth] and
pearl millet [Pennisetum americanum] which are consumed locally as staple food. Sorghum and
millet are resilient to the environment of the region. The legumes, cowpea [Vigna unguiculata
(L.) Walp.], groundnuts [Arachis hypogaea L.] and bamabara groundnut [Voandzeia
subterranean (L.) Thou] are both subsistence and cash crops. Early cowpea is harvested in
August to break the hunger gap. Other major crops grown in the region include yam [Dioscorea
spp.] and cotton [Gossypium hirsutum L.]. Although a large portion of these crops is consumed
directly in the region, regional self-sufficiency is rarely attained. Recently, soybean (Glycine
max) has gained prominence as a cash crop in the region due to its increasing importance both in
the domestic and export markets, and its products (oil and cake) for both domestic and industrial
uses. Soybean has an average protein content of 40-45% and is more protein-rich than any of the
common vegetables or animal food sources found in the region.
.
5
Figure 1: Agro-Ecological Zones of Ghana and the distribution of the Project Sites
6
Figure 2: Annual Rainfall distribution in Ghana
1.2. Objectives
The objectives of the study were to:
Establish the initial available plant nutrient levels for the selected fields in the various
communities within each of the 5 districts.
Examine the chemical properties and fertility status of the soils
Find out whether the pH of soils for the selected fields is suitable for soybean cultivation.
7
Examine the major physical characteristics of the soils within the communities in each
district and their effect on soybean production
Make recommendations on appropriate management practices including fertilization
programme for soybean production in the communities based on the initial soil test levels
of the various nutrients.
1.3 Methodology
The study mainly involved the examination of soils and sampling of three project communities
each from four districts (Wa East, Nadowli, Lambussie/Karni and Sissala West) and four from
Wa West district. In each community, a field to be cultivated was identified and soil samples
taken. In the field, soil observation was made at one project site in each community. It involved
auger bores to examine the soil for depth, drainage, texture and coarse fragment content. Bulk
samples were taken at 3 randomly selected points at a depth of 0-20 cm. Secondary soil
information was derived from detailed reconnaissance soil surveys of Lawra-Wa (Adu and
Asiamah, 2003).
2.0 RESULTS OF THE STUDY
2.1 Soils of the Upper West Region
Soils in the Upper West Region are largely developed over granite and few areas developed over
Lower Birimian phyllite. Most of the soils vary in depth ranging from < 30 to > 80cm with the
latter being dominant. In most cases, the soil types that dominate in UWR are laterite, sandy and
sandy loam (Savannah Ochrosols). They are generally poor in organic matter and nutrients as a
8
result of the absence of high vegetative cover, due to indiscriminate annual bush burning,
overgrazing, over-cultivation and protracted erosion, and the soils are heavily leached.
In all the communities where soils were sampled in this study, the soil texture is generally loamy
sand or sand for the topsoil (0-20 cm). Most of the sites occur on the middle slopes of 2 – 3%
and are moderately well drained. The major limitation of the soils is the sandy nature,
particularly in the topsoil (see Appendix 1 for particle size analysis). It makes them highly
susceptible to erosion.
2.2 Assessment of the observed sites for crop (soybean) production
Assessment of the suitability of the soils for soybean production is considered in the context of
other factors such as climate and relief. Soybean grows well under a wide range of temperatures,
but prefers a mean monthly maximum temperature above 20oC. The vegetative growth is slow
or nil at 10oC and optimum at 30
oC. Temperatures above 40
oC have an adverse effect on the
growth rate, flower initiation and pod formation. There are two critical periods regarding water
requirements in the growing cycle of soybean (and other food legumes): - the periods from
planting to emergence and the pod filling stage. The water consumption of soybean varies from
about 250 mm in dry situation to approximately 850 mm under optimal conditions. Only 25-30%
of the water consumed by the crop is used before flowering; 45% is used during the pod filling
period. Soybean recovers better than other crops from water deficits during the vegetative growth
stages, with its deep root system and relatively long flowering period, it can tolerate short
periods of moisture stress. The loss of early flowers and pods may be compensated for by those
flowers produced later when moisture becomes available again.
9
Rainfall and temperature in the UWR are adequate for the production of soybean and other
legumes and cereals. Although total annual rainfall is generally adequate, the onset and end of
the rainy season and the erratic distribution causes major problems in rain-fed crop production.
Historical rainfall figures show a consistent decrease in total amount of rainfall. Other than the
total amount of rainfall received in any particular year, rains in the region are characterized by
their unreliability and unpredictability, as well as their year-to-year variability, which has
important consequences on crop establishment. Thus measures to mitigate water deficit created
by the low rainfall are indispensable.
Soybean grows on a wide range of soils ranging from loamy sands to clay loams, provided they
are deep and well drained. Clay soils and soils with a tendency to cap may cause problems of
germination. The soil pH should be in the range of 5.0-5.2 for the best utilization of fertilizers
and the improvement of the soil environment. Acid soils should be limed to produce high
soybean yields. Although soybean varieties differ in their tolerance to soil acidity and
Aluminium toxicity, they will never yield as much on acid soils as on soils without acidity
constraints. In general, soils that are poorly drained should be avoided. Also, it should not be
grown in sandy, gravely, or shallow soils to avoid drought stress. Soil depth is a major limitation
in the UWR as the soils have shallow soil depth up to 50 cm which is rated marginal. Soil texture
is generally loamy sand or sand in the topsoil (Appendix 1). Only seven sites had clay content of
6% and above (Fig. 3). The soils are therefore highly susceptible to erosion and have low
moisture and nutrient holding capacity. This situation is aggravated by the generally low and
erratic rainfall.
10
Fig. 3: Clay content of the selected communities in the various districts
Note: The A, B, C, D, E labels for the districts are the communities as indicated in Table 1
2.3 Soil chemical properties
Soil Reaction:
The top soil pH ranged from 5.35 to 6.25 (Fig. 4) and this is generally suitable for legume
(soybean, cowpea and groundnut) production. Soil pH near 6.0 is desirable for producing optimum
soybean yields. Three sites (Wechiau, Kojokpere and Pulbaa) had top soil pH values greater than
6.0 and are therefore considered slightly acidic. Nonetheless majority (56%) of the sites had pH
values between 5.6 and 6.0 and are therefore considered to be moderately acidic. Furthermore,
five sites (Poyentanga, Naawie, Lambussie, Sorbelle and Jeffesi) had top soil pH values between
the range of 5.3 and 5.5 and are considered to be acidic and hence will require proper
management to ensure that these values do not decline further. Maintaining soil pH between 5.5
and 7.0 will enhance the availability of nutrients such as nitrogen (N) and phosphorus (P) as well
0
2
4
6
8
10
12
14
16
18
Cla
y c
on
ten
t (%
)
District
A B C D
11
as microbial breakdown of crop residues. However, soil acidity can present a limitation or stress
to soybean production. Low soil pH can limit soybean yields. Under low pH conditions, toxic
concentration of Aluminium (Al) and manganese (Mn) will occur in the soil solution and the
availability to the plants of nutrients such as calcium (Ca), magnesium (Mg), P and molybdenum
(Mo) becomes suboptimal. A low soil pH also adversely affects the N2 fixation. By regulating
soil microbial activities, the pH affects the mineralization of organic matter and the subsequent
availability of N, P and S and some of the micronutrients
Fig. 4: Top soil pH for the various sites
Note: The A, B, C, D, E labels for the districts are the communities as indicated in Table 1
Organic matter and Nitrogen status:
Top soil organic matter and N status of the various sites are presented in Figures 5 and 6. The
organic matter content ranged from 0.64 to 1.45%. and this is generally rated low The highest
organic matter content was obtained at Chogsie in the Wa East district where traditionally,
0
1
2
3
4
5
6
7
8
So
il p
H
District
A B C D
12
farmers can afford to restore soil fertility by long periods of bush fallow as the population
density is low and land is relatively not scarce. Five other sites (Poyentanga, Vieri, Loggu,
Goripie and Pulbaa) had organic matter values of >1.0%. On the whole, the organic matter
status of all the project communities is not encouraging and these data only buttress the fact that
in most parts of the region, soil nutrient depletion is a principal concern. Moreover, most of the
cultivated soils are inherently low in natural fertility and even the relatively better soils are
increasingly being depleted through many years of continuous cropping. The situation is most
critical in the Bulenga, Yaruu, Nyimatin and Sorbelle communities. It is worthy of note that soil
organic matter is critical in both nutrient and water retention. It is also a nutrient reservoir
holding and releasing nutrients during mineralization. Soil organic matter is even more critical
when the soils are sandy as in the project communities. Organic material is not easily available in
the savanna environment due to bush burning, the use of crop residue as fuel and animal grazing.
Soil nitrogen mostly originates from decomposing organic matter and explains the similarity in
Figures 5 and 6. . Total N of 0.10 % and above is good enough for plant growth. Most of the
sites showed rather very low values (<1.0%) emphasizing the need for adequate N supply for
better crop performance. Only the Pulbaa and Jeffisi communities had moderate levels of total N.
13
Fig. 5: Organic matter content of the various districts
Note: The A, B, C, D, E labels for the districts are the communities as indicated in Table 1
Fig. 5: Total nitrogen content of the various districts
Note: The A, B, C, D, E labels for the districts are the communities as indicated in Table 1
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2O
rga
nic
ma
tter
(%
)
District
A B C D
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
To
tal
N (
%)
District
A B C D
14
Available phosphorus:
About 88% of the sites have soils with very low to low P content (Fig. 7). Only two sites (Pulsaa
and Lambussie) had medium levels of available P. The availability of P is low in most savanna
soils with a high P-fixation capacity and the problem becomes more serious when the organic
matter status of the soil are low. P defiency reduces the efficiency of biological nitrogen fixation.
Figure 7: Available phosphorus for the various districts
Note: The A, B, C, D, E labels for the districts are the communities as indicated in Table 1
Exchangeable Potassium:
Exchangeable K for the sites are presented in Figure 8. Exchangeable K levels for most of the
communities are high. Only two sites (Goripie and Yarru) had moderate K values. Normally
even in areas where soils are believed to be well supplied with K, deficiencies may occur after a
few years of soybean cropping. Potassium deficiency cause retarded maturation, an increase in
the incidence of seed diseases and a reduction in seed quality.
0
1
2
3
4
5
6
7
8
9
10
11
12
Bra
p N
o 1
P (
mg
/kg
)
District
A B C D
15
Fig. 8. Exchangeable K for the selected districts
Note: The A, B, C, D, E labels for the districts are the communities as indicated in Table 1
3.0 CONCLUSIONS AND RECOMMENDATION
Generally, the soils in all the communities are suitable for the production of soybean but most of
the sites are marginal with shallow soil depth as the major limitation. Soils in the region have a
sandy texture (with 56% of the sites having clay content of less than 6 %.), low nutrient contents
and consequently a low moisture retention capacity. The soils therefore are prone to erosion. As
a result crops grown in the region are adversely affected by any least drought.
In general, the soils are low in plant nutrients such as N, P and contain little organic matter. Crop
residue removal can exacerbate soil nutrient depletion and hence soil productivity. Removal of
crop residue and natural vegetation, overgrazing, bush burning, indiscriminate cutting of trees for
fuel and construction have hastened erosion and degradation of the fragile soils of the region.
Traditionally, farmers can no longer afford to restore soil fertility by long periods of bush fallow
0
20
40
60
80
100
120
140
160
Exch
an
gea
ble
K (
mg
/kg
)
District
A B C D
16
as population increases and land becomes increasingly scarce. Crop residues are used as
livestock feed, fuel and construction materials. Calcium (Ca) and magnesium (Mg) also serve
many functions in the soybean plant and may be supplied in the soil. Application of Actyva™
(23-10-5+3+2+0.3 as N, P2O5, K2O, S, MgO and Zn) supplies the major nutrients N,P and K as
well as Mg, S and Zn. When Ca is also needed Yara legume™ (0+18+13+31+4+2 as N, P2O5,
K2O, CaO, S and MgO) can be used to suppy both Ca and Mg. Nevertheless, Yara legume™
may be used in addition to Rhizobium inoculants as this fertilizer does not contain N. Despite the
fact that soybean fixes atmospheric N for plant use, it is recommended that a small starter
fertilizer amount (25 kg/ha) be applied as basal dressing. The application of fertilizer is also
necessary because until nodulation occurs, the soybean plant depends on soil N for growth.
Adition of Ca and Mg in the form of liming should be done with caution as most of the soils in
the communities are poorly buffered. Organic sources (cow dung, fertisoil, compost,
incorporation of crop residue) should be preferred.
On the basis of the above, it is recommended that
1. MEDA-GROW Project takes cognizance of soil fertility improvement particularly on
organic matter build up and integrated soil fertility management.
2. Soybean is known for its efficient use of residual fertility and will therefore use any
residual fertilizers when it is grown in rotation with a cereal whereby the fertilizer is
applied to the cereal.
3. In case of direct fertilization of a soybean crop, nitrogen is usually recommended only if
the N status of the soil is low as in the case in all the project communities. The combined
use of mineral fertilizer with NPK and micronutrients (e.g. one bag Actyva fertilizer per
17
acre or Yara Legume fertilizer plus inoculants) and organic fertilizers (e.g., compost,
fertisoil, and farm yard manure) is necessary in order to increase yields and maintain soil
health. Any strategy to build up organic matter will depend on prevailing conditions in
that locality which will have to be explored by researchers.
4. One way by which N can be added to the soil is by biological nitrogen fixation (BNF) by
symbiotic N-fixing legumes, such as soybean, in symbiosis with rhizobial bacteria. The
soybean rhizobia are naturally found in large numbers in the soil close to the roots of the
plant. However, the bacteria can also be artificially introduced into the soil by a process
called inoculation. In many soils, the nodule bacteria are not adequate in either number or
quality, it is therefore necessary to apply the rhizobia (Rhizobium japonicum) as
inoculum to the seed before planting. If soybean is to be sown in any of the fields in the
various communities for the first time or where soybeans have not been successfully
grown within three years, inoculants containing nitrogen-fixing bacteria should be
applied at planting.
5. Erosion prevention practices be taken seriously firstly to maintain or preserve the current
precarious soil depth and secondly to prevent the washing away of the already depleted
soil nutrients. Of particular concern on erosion inducement is the inappropriate use of
tractors during ploughing. Animal traction as well as conservation agriculture practices
should be encouraged.
6. The project should use improved promiscuous soybean cultivars (cultivars that nodulate
well with diverse native rhizobia) together with organic and mineral fertilizers and
biological nitrogen fixation to increase yields and profits.
18
References
Adu, S. V. and Asiamah, R. D. 2003. Soils of the Lawra – Wa Region, Upper West
Region, Ghana. Memoir No. 18, soil Research Institute, Kumasi
Bray, R. H. and L. T. Kurtz 1945 Determination of total organic and available forms of
phosphorus in soil. Soil Science, 599: 39-45
Bouyoucous, G. J. 1962 Hydrometer method improved for making particle size analysis of soils.
Agron. Jour. 54: 464-465
Nelson, D. W. and Sommers, L. W. 1982 Total carbon, organic carbon and organic matter. In:
Page, A. L., R. H. Miller and D. R. Keeney (eds.). Methods of soil analysis. 2. Chemical and
Microbiological Properties. Agronomy 9: 301 – 312
Soils Laboratory Staff. Royal Tropical Institute 1984. Analytical methods of the service
Laboratory for soil, plant and water analysis. Part 1: Methods of soil analysis. Royal Tropical
Institute, Amsterdam
19
Appendix 1: Chemical and physical analysis of soil samples of the selected project sites
District community pH O.C (%) OM (%) TN (%) Bray P
(mg/kg)
Available
K (mg/kg)
Particle size Analysis
% Sand %
Silt
% Clay Texture
Wa West 0-
20 cm
Wechiau 6.06 0.46 0.80 0.09 8.94 123.04 93.64 0.16 6.20 Sand
Poyentanga 5.52 0.77 1.32 0.07 9.20 125.30 95.60 0.36 4.04 Sand
Vieri 5.95 0.69 1,20 0.06 7.86 113.58 95.20 0.88 3.92 Sand
Chogsie 5.75 0.92 1.58 0.07 9.04 123.95 93.20 2.84 3.96 Sand
Wa East
0-20 cm
Bulenga 5.63 0.37 0.64 0.08 9.77 130.26 87.20 4.88 7.92 Loamy sand
Loggu 5.72 0.73 1.26 0.09 8.99 123.49 77.20 10.88 11.92 Sandy loam
Goripie 5.97 0.66 1.14 0.09 9.41 98.71 83.20 8.88 7.92 Loamy sand
Nadowli
0-20 cm
Kojokpere 6.04 0.41 0.71 0.09 9.56 113.58 97.36 0.72 1.92 Sand
Yaruu 5.89 0.38 0.66 0.05 7.86 98.25 97.40 0.68 1.92 Sand
Pulbaa 6.25 0.84 1.45 0.11 10.34 137.47 89.28 4.84 5.88 Sand
Lambussie-
Karni
0-20 cm
Samoa 5.81 0.48 0.82 0.07 8.17 116.28 97.28 0.84 1.88 Sand
Lambussie 5.40 0.52 0.90 0.07 10.08 127.10 80.04 14.04 5.92 Loamy sand
Naawie 5.37 0.44 0.76 0.06 9.82 112.23 87.28 4.84 7.92 Loamy sand
Sissala West Nyimatin 5.98 0.38 0.66 0.08 8.63 120.34 97.28 0.80 1.92 Sand
Sorbelle 5.39 0.38 0.66 0.06 9.15 124.85 87.28 4.80 7.92 Loamy sand
Jeffisi 5.35 0.43 0.75 0.10 8.22 116.73 87.28 4.80 7.92 Loamy sand
20
Appendix 2: Methods of laboratory analyses
The following parameters were determined in the laboratory:
Soil pH was determined in a 1:1 suspension of soil and water using a HI 9017 microprocessor glass electrode pH meter.
Organic matter was determined by a modified Walkley and Black procedure as described by Nelson and Sommers (1982).
Total nitrogen was determined by the Kjeldahl digestion and distillation procedure as described in Soil Laboraotry Staff
(1984).
Exchangeable bases (calcium, magnesium, potassium and sodium) in the soil were determined in 1.0 M ammonium acetate
(NH4OAc) extract (Black, 1986).
Exchangeable acidity (hydrogen and aluminium) was determined in 1.0 M KCl extract as described by Page (1982).
Available phosphorus was determined by the Bray-1 method as described by Bray and Kurtz (1945). Particle size distribution
was determined by the hydrometer method.
Texture (sand, silt and clay) was determined by the hydrometer method as described by Bouyoucos (1962).
21
Appendix 3: Upper West Region Soil suitability map
