Hydrogeological Studies on Soils Developed Over Granitic Deposits

IJAAR 2 (2014) 29-40 ISSN 2053-1265

Hydrogeological studies on soils developed over granitic deposits

Gyamera E. A.1, Kuma J. S.2 and Okae-Anti D.1*

1Department of Soil Science, School of Agriculture, University of Cape Coast, Cape Coast. Ghana. 2Department of Geological Engineering, University of Mines and Technology, Tarkwa, Ghana.

Article History ABSTRACT Received 23 July, 2013 The objective of the study was to investigate whether soils derived from granitic Received in revised form 08 deposits held a clue to moisture availability and retention in a relatively dry January, 2014 Accepted 15 January, 2014 ecology and hence able to sustain agricultural production. A parcel of land covering 400 acres in Twifo Nwomaso of the Twifo Hemang Lower Denkyira Key words: District of the Central Region was assessed for its hydrogeological potential. Topography, Twenty sample locations were tested for particle size distribution, bulk density, Cape Coast granite, moisture content, infiltration rate, hydraulic conductivity, Atterberg limits and Physical analysis, pH; at depths of 0.5 m and 1.0 m in each location. Meteorological characteristics Contouring, and topographic survey were also analyzed and conducted respectively to Twifo Hemang Lower identify the run-off pattern, as well as, the direction of flow. Results obtained Denkyira District. indicate that the topography of the survey area was relatively undulating with elevations between 260 and 400 m above mean sea level. In view of this, the direction of runoff flow is expected to be distributed over the entire land. The site is dominated by well graded mineral particles of sandy loam to loamy sand -1 textures. Infiltration of precipitation into the subsurface is at 0.026 cm s . Soils located in the low relief areas were expected to be the discharge points. Rainfall pattern is grossly consistent over the area. The site would be suitable for Article Type sustainable agricultural activities since the hydrogeological attributes are fairly Full Length Research Article consistent and stable. The pH of soils is within moderate acidity. ©2013 BluePen Journals Ltd. All rights reserved

INTRODUCTION

The Twifo Hemang Lower Denkyira District (THLDD) lies harmattan conditions during which visibility reduces within Latitude 05° 37’ N and Longitude 01° 32’ W on considerably. The major rainy season begins from May to altitudes of 60 to 1000 m above mean sea level. The area July while the minor season begins in August through to is generally hot with a temperature ranging between 26ºC November. Figure 1 shows a rainfall pattern over a 10- and 32ºC with relative humidity ranging from 65-75%. year period, taken at the Cape Coast Regional The highest mean temperatures occur between March Meteorological Station, some 30 km away. Wind direction and April whereas the lowest are recorded in August. is mainly south westerly with a speed of about 5 knots. The annual average rainfall is between 900 and 1600 The area consists of secondary forests and large tracts of mm with the heaviest occurring in June. There is however forest reserves, covering about 24% of the entire district. a dry period from December to about the month of April The area is drained by River Pra and its tributaries, which when the North East Trade Winds set in, bringing take their source from the top of the series of ridges cutting across the strike of rocks. The courses of these rivers have been attributed to faulting, jointing and softening of rock by weathering. Basic granitic intrusives *Corresponding author. E-mail: [email protected]; Tel. and granites underlie almost all the study area. Major +233 24 472 1136; Fax. +233 33 213 2709. rock types comprise well - foliated, medium - grained,

Int. J. Adv. Agric. Res. 30

350

300

250

200

150 Rainfall (mm) Rainfall 100

Month

Figure 1. Rainfall pattern inclusive of the study area over a period of ten years.

potash-rich muscovite-biotite granites, grano-diorites and MATERIALS AND METHODS pegmatites. Granites found in the study area are post Tarkwaian and can be divided into three groups: Bongo Soil sampling Granites, Dixcove Granite Complex and Cape Coast Granite complex. The Cape Coast granites are often A base line (BL) was constructed that stretched along the associated with schists and gneisses, and intrude the northern end of the study site. A number of transects lower Birimian meta-sediments. One characteristic of the (cross lines – CL) were then established perpendicular to granite is that it is not inherently permeable, but the base line at a constant interval of 200 m. Appropriate secondary permeability and porosity have developed as a sample sites were located and pegged along the base result of fracturing and weathering. The hydraulic line and transects. The number of samples (S) needed to potential depends on the degree of fracturing and on the be taken at the field was determined based on the potential recharge of the aquifer, which is directly related amount of variability within the field. The following factors to the annual rainfall and water streaming. Groundwater were carefully considered: The size of the field, slopes, occurs mainly in fractured portions of the bedrock. primary and secondary vegetation, cropping history, However, some amount of water may be obtained from history of manure application, drainage and erosion. the overburden and at the interface between the Once the sample points were defined, they were marked overburden and the bedrock. Borehole yields are and then labelled with unique numbers such as CL1S1, variable, varying between 0.2 and 15 m3 h-1 depending BL1S4 and BL1S2, etc. Forty (40) representative sam- upon the degree and intensity of fractures in the ples were collected from 20 profile pits at the 0.5 and 1.0 underlying bedrock. Borehole depths are medium, m depths, plus additional 10 for quality control analysis in ranging between 20 and 50 m. Aquifers have been the laboratory. intercepted at various depths ranging from 7 to 30 m with However, in a few cases, the depth of 1.0 m was not a mean value of 27 m. A mean static water level of 5.20 achieved because ground water was intercepted at about m has also been found from existing borehole records 0.6 m. The Stratus Geographic Positioning System (GPS) (Anon, 2008). was used to ascertain the coordinates of all sample

Gyamera et al. 31

points for plotting purposes. The study covered the Assin North and South Districts. The District has a total period, November 2010 to April 2011. land area of 1,199 km2 and 1,510 community settlements, Standard field and laboratory techniques were followed eight Area Councils and four paramountcy, namely: at the Geotechnical Laboratory and the Soil Science Hemang, Denkyira, Twifo and Atti Morkwa. Laboratory at the University of Mines and Technology, The study area is also rich in mineral deposits (Figure Tarkwa and the University of Cape Coast, Cape Coast, 3). The minerals found in the district include: Gold at respectively. The following parameters were determined: Mfuom, River Botro and Afiafiso, Diamond at Afiafiso; particle size distribution - by dry sieving and sedimen- and Manganese at Asamang and Mampong. Birimian tation method; bulk density - soil specimens were slashed and Tarkwaian rocks can be found within the Pra River into regular shapes and pieces, weighing between 80 to which holds the potential for the exploitation of Gold and 150 g. At least for each sample, three labelled specimens Manganese. The bed of River Pra also contains alluvial were prepared for the density test while three were also gold deposits. The rocks in the Pra River (for example, prepared for moisture content test. The specimens were Wamaso albitized granodiorite) can also be used for then coated with paraffin wax and again weighed. A piece quarrying. The Pra River could also be used for fishing. of thread was tied around the specimens and gently However, this activity is limited by the presence of large lowered into beaker containing the water until it was fully rock outcrops, which prevent the use of canoes on a submerged. Care was taken such that the specimens did large scale. not touch any part of the beaker. The volume of water Tables 1 and 2 give summaries of the physical displaced in cm3 was recorded; moisture content - by properties and chemical composition of the Cape Coast measurement of wet and oven-dried weights of the test granite. Chemically, granitic rocks are either of igneous or specimens, using a 0.01 sensitivity electronic balance; metamorphic origin, composed of quartz, feldspar and infiltration rate - by the double ring infiltrometer; hydraulic ferromagnesian minerals. Typical granite will have the conductivity - by Darcy’s law, where the volume rate of chemical composition shown in Table 2. flow of water was measured across a plane normal to the Figure 4 shows results of the topographic survey of the direction of flow; Atterberg limits - by the Cassagrande study area at a scale of 1:2500. It is observed that the liquid limit and the plastic limit method; pH - determined elevations between 260 and 400 m above mean sea level by weighing 10 g of air-dry soil sample into a centrifuge dominate the study area. The topography is relatively bottle, and adding 25 ml of distilled water after which the undulating. In view of this, the direction of runoff flow is bottle was shaken horizontally for 15 min: the resulting expected to be uniformly distributed over the entire study suspension was measured using a potentiometric electric area. pH meter after the meter had been calibrated using a Since the gradient of the ground surface of the study buffer of pH 4 and 7; meteorological data was obtained area is undulating, and runoff is expected to flow over from the regional meteorological station, located about 30 most of the land, it will enhance infiltration of precipitation km from the study site; topographic survey - by grids into the subsurface and that will enhance plant growth. formed out of the base line and cross lines at intervals of Low relief areas were associated with ground water 50 m: wooden pegs were used to mark out all points that discharge points. were considered and with the Stratus Global Positioning However with better sorting coefficient and Ks value, System, the x, y and z coordinates of points were picked precipitation recharge will be better in those areas and which were then plotted at a scale of 1:2500 using the are expected to act as low-yielding regolith aquifers software SURFER. compared to the high relief areas. Isolated swamps observed may be ‘outcrops’ of shallow water tables in areas underlain by sandstones. Kuma and Younger RESULTS AND DISCUSSION (2002) noted that some of the possible reasons, in

As shown in the Figure 2, Twifo Nwomaso, hosting the addition to outcropping water tables, which may account study site, is located in the south central portion of for these swamps were: Ghana. It is within the THLDD in the Central Region. The study site is about 15 km North-West of the Pra River . weathering of the rocks, in part, to clay soils resulting from Twifo Praso, the District Capital, along the main in low infiltration capacities, Twifo Praso–Dunkwa-on-Offin road. . annual rainfall of over 1750 mm exceeding the THLDD is one of the thirteen (13) Districts in the holding capacity and/or transmissive properties of the Central Region of Ghana. THLDD is bounded on the regolith aquifers, and; North by the Upper Denkyira District; to the South by the . unweathered bed rocks being closed to the surface Abura-Asebu-Kwaman-Kese District, Cape Coast District and its storage, and transmissive properties being too low and Komenda-Edina-Eguafo-Abirem District; on the West to accommodate large volumes of recharge during short by the Wassa-Mpohor District; and on the East by the periods of time.

Int. J. Adv. Agric. Res. 32

Figure 2. Map of Ghana showing the study area. Source: Ghana Geological Survey Department.

Gyamera et al. 33

Figure 3. A section of the geological map of Ghana showing the study area.

Int. J. Adv. Agric. Res. 34

CL1S2 202800N CL1S1 BL1S1 202600N CL1S13 CL1S3 BL1S2 BL1S3 202400N CL2S4 CL4S7 BL1S4 CL2S3 CL3S6 202200N CL4S1 CL4S8

202000N CL6S10 CL5S9 BL1S6

CL5S10 201800N BL1S7

CL6S12 201600N 114000E 114200E 114400E 114600E 114800E 115000E 115200E

0 200 400 600 800

* Sample • Control Direction of flow Lowest relief zone

points. Figure 4. A detailed contour map of thepoints study area showing direction of flow.

Gyamera et al. 35

Table 1. Physical properties of the Cape Coast granite. soils. These were calculated from the effective size D10,

D30 and D60 of the soil. The formulae are stated below: Property Scaling Hardness 6 to 7 on Moh's Scale Cu = D60/ D10 (1) Density 2.6 to 2.8 kg cm-3 -2 2 Compressive strength 140 to 210 N mm Cc = (D30) /D10* D60 (2) Modulus of rupture 15 to 25 N mm-2 Water absorption 0.1-0.6% The textural class of the soils at each location is shown in Average wear Less than 1% Table 4. While the bulk densities of the soils are Porosity Quite low displayed in Table 5. Weather impact Resistant The bulk density of a soil plays an important role in determining if the soil has the physical characteristics Source: Anon (1996). necessary for plant growth, building foundations and

other uses. One significant inference of bulk density of soil is the amount of surface area a soil has. Large Table 2. Chemical composition of Cape Coast granite. surface area of the soil implies greater ability to retain water and nutrients. Lower bulk density implies greater Property Scaling surface area. The bulk density of soils greatly depends on the mineral makeup and the degree of compaction. Silica (SiO2) 70-75% Bulk densities are always equal to half the soil particle Al O 10-15% 2 3 density and inversely related to its porosity. Typical CaO + MgO Less than 0.5% organic soils are those with densities between 1.1 and FeO + Fe2O3 2-4% 2.0 ton m-3. Alkalis 4-6% From Table 5, the average bulk densities for the soils -3 TiO2 Less than 0.5% are 1.88 and 1.92 ton m at the depths of 0.5 and 1.0 m Loss on ignition (LOI) Less than 0.5% respectively. It is observed that, in most of the sample

Source: Anon (1996). points, the bulk density values increases with depth. This is due to the effect of cultivation and the decrease of organic matter content with depth. The bulk density values for the soils are relatively high and may cause Figure 5 shows the grain size distribution curves for hindrance to root penetration if the ground is not sample BL1S1 at 0.5 and 1.0 m depth from the surface. It prepared well for cultivation. This increase in density will is observed from Figure 5 that less than 50% of the cause a decrease in permeability, thereby making field samples passed through the 0.075 mm sieve for both crops more susceptible to the adverse effects of water depths, indicating: coarse grained soil with about 30-40% logging. fines. The size fraction indicates that both the plasticity The infiltration rate test was conducted on the soils in and grain size distribution might have a significant effect order to determine field capacity levels for irrigation on the engineering properties of the soil. The graphs also purposes. The field observation was conducted in the dry show well grading of the soil at both levels (Shahid et al., season, because at that time, all the macro pores open to 2012). Similar graphs were plotted for the remaining the surface and are available to conduct water into the samples. From the results of the various graphs, the soils soil. In the soil with expanding type of clays, the initial have been characterized as either as distinctly well infiltration was particularly higher as water poured into the graded or uniformly graded (Table 3). network of the shrinkage cracks. Consequently, the The grading of the soil was determined by direct sudden decrease in infiltration rate was due to the closing observation of the particle size distribution curve. That is: up of shrinkage cracks because many macro pores would if the shape of the curve is not too steep but more or less have been filled with water. constant over the full range of the soil’s particle sizes, A graph of infiltration rate (cm s-1) was plotted against and the particle size distribution extends evenly over the time in seconds to determine the infiltration rate of the range of the particle sizes within the soil with no soil (Figure 6). Similar graphs were plotted for the deficiency or excess of any particular particle size, then sampling sites. The temperature and the relative humidity the soil is said to be well graded. Any other form of of the soils were determined by using a digital thermo- distribution curve than the former is said to be poorly hydrograph. graded. However, for some guidance, the uniformity The average infiltration rate for the site was found to be coefficient (Cu) and coefficient of curvature (Cc) of the 0.026 cm s-1 which seemed to support the observation soils were also calculated in order to aid in the that the site was predominantly of sandy loam textures. It characterization based on the uniformity and grade of the also meant that in the dry season, the application rate of

Int. J. Adv. Agric. Res. 36

Clay Silt Sand Gravel

)

(

passing

entage

erc P

Particle size (mm)

Figure 5. Grain size distribution curve for sample BL1S1.

Table 3. Cu and Cc of the soils.

Sample No. D10 D30 D60 Cu Cc Sample no D10 D30 D60 Cu Cc BL1 S1 0.5 m 0.006 0.060 2.90 483.3 0.21 BL1S5 0.5 m 0.005 0.600 5.00 925.9 13.33 BL1 S1 0.9 m 0.017 1.40 BL1 S5 1.0 m 0.016 0.75

CL1 S1 0.5 m 0.009 0.21 CL4 S7 0.5 m 0.013 0.30

CL1 S1 1.0 m 0.014 2.50 CL4 S7 1.0 m 0.150 1.800 3.50 23.3 6.17

CL1 S2 0.5 m 0.061 2.00 CL4 S8 0.5 m 0.007 0.13

CL1 S2 1.0 m 0.042 0.40 CL4 S8 1.0 m 0.018 0.59

BL1 S2 0.5 m 0.013 2.30 BL1 S6 0.5 m 0.008 0.600 6.00 750.0 7.50

BL1 S2 1.0 m 0.005 0.06 BL1 S6 1.0 m 0.013 0.21

CL1 S3 0.5 m 0.003 0.400 2.00 666.7 26.67 CL5 S9 0.5 m 0.050 1.80

CL1 S3 1.0 m 0.015 2.20 CL5 S9 1.0 m 0.021 0.21

BL1 S3 0.5 m 0.009 0.150 6.00 666.7 0.42 CL5 S10 0.5 m 0.090 0.300 2.90 32.2 0.34 BL1 S3 1.0 m 0.060 1.50 CL5 S10 1.0 m 0.021 2.00

CL1 S4 0.4 m 0.075 0.240 0.55 7.3 1.40 BL1 S7 0.5 m 0.008 0.055 0.33 41.3 1.15 CL1 S4 0.6 m 0.075 0.190 0.47 6.3 1.02 BL1 S7 1.0 m 0.017 0.29

BL1 S1 0.5 m 0.003 0.085 0.78 300.0 3.56 CL6 S11 0.5 m 0.002 0.20

BL1S4 1.0 m 0.003 0.040 0.69 230.0 0.77 CL6 S11 1.0 m 0.004 0.097 0.65 154.8 3.45 CL3 S5 0.5 m 0.005 0.240 1.60 320.0 7.20 CL6 S12 0.5 m 0.002 0.010 0.25 138.9 0.22 CL3 S5 1.0 m 0.014 1.25 CL6 S12 1.0 m 0.006 0.15

CL3 S6 0.5 m 0.090 0.230 0.49 5.4 1.20 CL1 S13 0.5 m 0.017 3.00

CL3 S6 1.0 m 0.180 0.390 0.90 5.0 0.94 CL1 S131.0 m 0.004 0.220 0.90 225.0 13.44

If Cu < 4.0 then the soil is uniformly graded. If Cu > 4.0 then the soil is well graded.

Gyamera et al. 37

Table 4. Textural classes of the soils.

Sample Percentage grain fraction Texture Sample No. Location Gravel Sand Silt Clay 0.5 m 8.63 68.30 11.57 11.50 Sandy Loam CL1 S1 1.0 m 41.38 37.41 14.71 6.50 Loamy Sand 0.5 m 39.40 43.34 13.56 3.70 Loamy Sand CL1 S2 1.0 m 24.87 40.54 15.09 19.50 Sandy Loam 0.5 m 41.88 33.25 16.56 8.30 Sandy Loam BL1 S2 1.0 m 11.51 55.62 22.77 10.10 Sandy Loam 0.5 m 49.24 34.47 5.39 10.90 Loamy Sand CL1 S3 1.0 m 18.24 49.94 22.02 9.80 Sandy Loam 0.5 m 49.28 44.87 2.92 2.93 Sand BL1 S3 1.0 m 41.88 36.53 14.94 6.64 Loamy Sand 0.5 m 4.72 92.54 1.74 1.00 Sand CL1 S4 1.0 m 4.25 93.17 1.07 1.50 Sand 0.5 m 17.68 66.35 7.97 8.00 Loamy Sand BL1 S4 1.0 m 17.48 62.98 5.64 13.90 Sandy Loam 0.5 m 30.58 58.71 7.90 2.81 Sand CL3 S5 1.0 m 22.81 54.61 22.58 0.00 Loamy Sand 0.5 m 5.49 93.32 0.00 1.20 Sand CL3 S6 1.0 m 11.06 88.25 0.09 0.60 Sand 0.5 m 63.27 25.76 2.97 8.00 Sand BL1 S5 1.0 m 31.78 45.88 14.30 8.04 Loamy Sand 0.5 m 8.70 70.07 16.70 4.53 Loamy Sand CL4 S8 1.0 m 6.67 49.29 39.44 4.60 Sandy Loam 0.5 m 63.27 28.76 3.97 4.00 Sand BL1 S6 1.0 m 12.10 65.20 8.30 14.41 Sandy Loam 0.5 m 35.71 40.02 19.17 5.10 Sandy Loam CL5 S9 1.0 m 11.19 65.18 15.03 8.60 Sandy Loam 0.5 m 52.38 40.80 3.94 2.88 Sand CL5 S10 1.0 m 39.32 43.04 11.24 6.40 Loamy Sand 0.5 m 5.17 87.09 3.90 3.84 Sand BL1 S7 1.0 m 3.39 74.68 17.23 4.70 Sandy Loam 0.5 m 7.30 55.92 29.00 7.78 Sandy Loam CL6 S11 1.0 m 12.82 74.32 4.30 8.56 Sand 0.5 m 18.31 55.34 13.20 13.15 Sandy Loam CL6 S12 1.0 m 13.29 59.18 9.20 18.33 Sandy Loam 0.5 m 49.24 28.97 14.99 6.80 Loamy Sand CL1 S13 1.0 m 13.50 74.71 7.30 4.50 Sand 0.5 m 7.26 65.18 21.10 6.46 Sandy Loam CL4 S7 1.0 m 63.98 31.94 1.47 2.60 Sand 0.5 m 49.94 38.93 6.18 4.95 Sand BL1 S1 1.0 m 33.34 48.99 10.60 7.07 Loamy sand

water that would be sufficient to saturate the soil for plant amount of clay might be present at such locations. support should be 0.026 cm s-1. The range falls within Conversely, the high value of 9.9 × 10-1 cm s-1 was an 0.013 to 0.041 cm s-1 and that corresponds to soil types indication of the presence of coarse grained sand. from clay loam to sandy loam (Brady and Weil, 2002; If the soil supports natural vegetation, particularly Singer and Munns, 2006). However, the lower values (8 × forest, the ground surface will usually consist largely of 10-3 and 9 × 10-3 cm s-1) indicate that a relatively high leaf litter, humus, and other organic matter that has a

Int. J. Adv. Agric. Res. 38

)

(

rate

Infiltration

Time (s)

Figure 6. Graph for the determination of infiltration rate of the soil at BL1S2.

Table 5. Bulk and dry densities of soil samples.

At 0.5 m At 1.0 m Location Av. bulk density Av. dry bulk density (t m-3) Av. bulk density Av. dry bulk density (t m-3) BL1 S1 0.5 m 1.89 1.58 2 1.79 CL1 S1 0.5 m 1.77 1.49 1.87 1.59 CL1 S2 0.5 m 1.78 1.45 1.89 1.65 BL1 S2 0.5 m 1.84 1.48 1.79 1.44 CL1 S3 0.5 m 1.8 1.45 1.71 1.45 BL1 S3 0.5 m 1.94 1.7 1.95 1.64 CL1 S4 0.4 m 2.12 1.84 2.09 1.77 BL1 S4 0.5 m 1.89 1.7 1.94 1.77 CL3 S5 0.5 m 2.09 1.87 2.01 1.83 CL3 S6 0.5 m 1.89 1.68 1.98 1.71 BL1 S5 0.5 m 1.76 1.41 2.07 1.81 CL4 S7 0.5 m 1.87 1.6 1.88 1.64 CL4 S8 0.5 m 1.83 1.55 1.91 1.67 BL1 S6 0.5 m 1.85 1.57 1.82 1.52 CL5 S9 0.5 m 1.86 1.54 1.85 1.57 CL5 S10 0.5 m 1.9 1.63 1.95 1.72 BL1 S7 0.5 m 1.92 1.64 1.97 1.7 CL6 S11 0.5 m 1.77 1.39 Particle size (mm) 1.82 1.51 CL6 S12 0.5 m 1.77 1.4 1.81 1.43 CL1 S13 0.5 m 2.08 1.87 2.09 1.9 Mean 1.88 1.59 1.92 1.66 Maximum 2.12 1.87 2.09 1.9 Minimum 1.76 1.39 1.71 1.43 Std. deviation 0.108 0.150 0.104 0.137 95% Conf. Int 0.047 0.066 0.0457 0.060 Std. Error 0.024 0.034 0.023 0.031

Gyamera et al. 39

Table 6. Hydraulic conductivities of the soils.

Sample location Depth (m) Hydraulic conductivity (cm hr-1) 0.5 0.183 ± 0.090 CL1S1 1.0 0.163 ± 0.112 0.5 0.189 ± 0.093 CL1S2 1.0 0.183 ± 0.112 0.5 0.178 ± 0.090 CL1S3 1.0 0.129 ± 0.112 0.5 0.124 ± 0.093 CL1S3 1.0 0.220 ± 0.112 0.5 0.250 ± 0.090 CL3S5 1.0 0.252 ± 0.112 0.5 0.264 ± 0.090 CL4S7 1.0 0.360 ± 0.112 0.5 0.380 ± 0.090 CL4S8 1.0 0.385 ± 0.112 0.5 0.372 ± 0.090 CL5S9 1.0 0.369 ± 0.112 0.5 0.395 ± 0.093 CL5S10 1.0 0.252 ± 0.112 0.5 0.265 ± 0.093 CL6S11 1.0 0.272 ± 0.112 0.5 0.248 ± 0.090 CL6S12 1.0 0.244 ± 0.112 0.5 0.241 ± 0.090 BL1S1 1.0 0.517 ± 0.112 0.5 0.131 ± 0.090 BL1S4 1.0 0.145 ± 0.112 0.5 0.132 ± 0.090 BL1S5 1.0 0.146 ± 0.112 0.5 0.160 ± 0.090 BL1S6 1.0 0.184 ± 0.112 0.5 0.192 ± 0.090 BL1S7 1.0 0.178 ± 0.112 0.5 0.144 ± 0.003 BL1S2 1.0 0.146 ± 0.112 0.5 0.351 ± 0.090 BL1S3 1.0 0.365 ± 0.112

For 0.5 m depth For 1.0 m depth Average 0.234 cm hr-1 0.245 cm hr-1 Maximum 0.395 cm hr-1 0.518 cm hr-1 Minimum 0.124 cm hr-1 0.119 cm hr-1 Range 0.271 cm hr-1 0.398 cm hr-1 Std. error 0.021 0.027

large number of large openings, and hence, a high surface porosity and permeability and limit infiltration hydraulic conductivity, regardless of the texture of the (Dingman, 1994). mineral soil. During the rainy season or during a single Table 6 presents the average hydraulic conductivity rain storm, clay minerals swell reducing the effective values for soil of the study area. The average hydraulic

Int. J. Adv. Agric. Res. 40

Table 7. Summary statistics of pH of the soils.

Statistic 0.5 (m) 1.0 (m) Mean 4.8 4.6 Maximum 6.4 7.4 Minimum 3.6 3.6 Std. deviation 0.944 1.205 95% Conf. Interval 0.449 0.573 Std. Error 0.229 0.292

conductivity is 0.234 cm hr-1 for the 0.5 m depth. This mean sea level. In view of this, the direction of runoff flow result is indicative of the soil texture of the site. The value is expected to be distributed over the entire land. Since of 0.234 cm hr-1 is very slow according to the conductivity the gradient of the land is gentle and runoff is expected to classification of FAO (1963), which gave conductivity flow over most of the land, it will enhance infiltration of classes and their respective values as: very slow = < 0.8; precipitation into the subsurface and that will enhance slow = 0.8 – 2.0; moderately rapid = 6.0 – 8.0; rapid = 8.0 plant growth. Soil located in the low relief areas are the – 12.5 and very rapid = > 12.5 cm hr-1. Again, the discharge points. average hydraulic conductivity value of 0.234 cm hr-1 2. Well-graded mineral particles constituting sandy loam recorded at the site also implies that the texture of soil textures mainly. These soils are capable of allowing might be clay, silty clay, clay loam or sandy clay loam. water to pass through at a rate of 0.026 cm s-1 over the Sandy clay loam seems to dominate the site. This value dry period. also implies that when drainage is necessary, close 3. The rainfall pattern is fairly consistent and uniformly drainage spacing is required and where necessary, sub- distributed. soiling is advocated to facilitate drainage at the site. The 4. At the level of soil reaction (pH) mobility of ions will sub-layer hydraulic conductivity value of 0.245 cm hr-1 is be enhanced. equally categorised as very slow. Should such soils be inundated with flood water, drainage gutters may be required in order to facilitate drainage. REFERENCES Plants have different tolerances for soil acidity. The pH Anon (1996). Detailed environmental impact assessment report for level of the soil directly affects soil life and the availability Goldfields Ghana Limited, Tarkwa Mine. Steffen, Roberts and Kirsten of essential soil nutrients for plant growth. Table 7 gives a Report 207102. 140p. summary statistics of the data on soil pH at the site. The Anon (2008). Technical report on the small towns’ water supply and most common range of soil pH is 4.0 to 8.0 and the range sanitation project in central and western region of Ghana. Pp. 10-17. Brady N. C. & Weil R. R. (2002). The nature and properties of soils, 13th for optimal availability of plant nutrients for most crops is Edition. Prentice-Hall Inc. New Jersey. 6.5 – 7.0. The average pH value of the 0.5 and 1.0 m Kuma J. S. & Younger P. L. (2000). Conceptual ground water model depth of soil sample is 4.8 and 4.6 with standard and related environmental concerns in the Tarkwa area, Ghana. deviations of 0.944 and 1.205 units, respectively. The Ghana Mining Journal 6:42-52. Shahid S. A., Taha F. K. & Abdelfattah M. A. (2012). Developments in values fall within the most common range of soil pH. soil classification, land use planning and policy implications. When soil is acidic, minerals such as zinc, aluminium, Innovative Thinking of Soil Inventory for Land Use Planning and manganese, copper and cobalt are soluble and available Management of Land Resources. Springer, ISBN: 978-94-007-5331- 0. 766p. for plant uptake. However, they can also be present in th Singer M. J. & Munns D. N, (2006). Soils: An introduction, 6 Edition. excessive amounts and therefore toxic to plants. Alkaline Prentice Hall. New York. soil on the other hand, may contain a higher quantity of bicarbonate ions and this can affect optimum growth in plants by interfering with the normal uptake of other ions. The study area is strongly acidic with small portions being medium to slightly acidic.

Conclusions

1. The topography of the survey area is relatively undulating with elevation between 260 and 400 m above