Characteristics and classification of soils derived from Awi ......Characteristics and...

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( Received 28 September 2018; Accepted 11 October 2018; Date of Publication 13 October 2018 )

WSN 112 (2018) 142-152 EISSN 2392-2192

Characteristics and classification of soils derived from Awi sandstone formation in Awi, Akamkpa

local government area of Cross River State, Nigeria

E. E. Aki* and V. E. Ediene

Department of Soil Science, University of Calabar, Calabar, Nigeria

*E-mail address: [email protected]

ABSTRACT

Soils derived from Awi sandstone formation in Awi, Akamkpa LGA of Cross River State, Nigeria

were studied along a toposequence with a view to classifying them taxonomically, assessing their

potentials and suggesting appropriate management strategies. Three profiles were dug at the crest,

middle slope and lower slope of the landscape. The morphological properties of these soils: colour, soil

structure, soil consistence, drainage, boundaries and root inclusions were recorded in the field. These

soils were deep (>100 cm), with sandy loam surface texture over sandy clay to sandy clay loam

subsurface textures. These soils had hues of 10 YR - 5 YR with sub angular blocky structure and a sticky

consistence (wet) and bulk density of 1.0 - 1.7 g/cm3 with total porosity of 22 - 38 %. Soil reactions in

H2O were acidic (pH 4.7- 5.8). These soils have Organic Carbon of 14.4 - 38.1 g/kg; total nitrogen 1.2

- 3.3 g/kg; available phosphorus 4.1- 8.3 mg/kg; exchangeable acidity (H+) 0.5 - 11.9 cmol/kg; Cation

Exchange Capacity (CEC) 2.0 - 6.0 cmol/kg and base saturation 20.0 - 52.5 %. The soils were classified

according to the USDA Soil Taxonomy as Typic Kandiudults and correlated as Dystric Acrisols as per

FAO- WRB for soil resources. It is recommended that soils fertility management practices should focus

on reducing leaching of basic cations from the soils through mulching, planting of cover crops, crop

rotation, adoptions of zero tillage as well as planting of acid tolerant crops and application of liming

materials to reduce the strong acidity in these soils.

Keywords: Awi sandstone, toposequence, soil taxonomy, soil morphology, Nigeria

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World Scientific News 112 (2018) 142-152

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1. INTRODUCTION

Sand stone are coarse grained, sedimentary rock consisting of consolidated masses of

sand deposited by moving water or by wind. The chemical constitution of sandstone is the same

as that of sand owing to the nature of the parent material (rock) which is basically composed of

quartz. The cementing material binding together the grains of sand is usually composed of

silica, calcium carbonate, or iron oxide.

The colour of the rock is often imparted largely by the cementing material, with iron

oxides causing red or reddish brown sandstones, and the other materials producing white,

yellowish or grayish sandstone. When sandstone splits, the cementing is fractured but the

individual grains remain whole, thus giving a granular surface appearance. The soils of Awi

though developed on sand stone parent materials fit into the order Utisols [1].

The Surfaces of these soils have been reported to have grayish brown (10YR5/2), fine

sandy loam texture with moderate crumb structure over subsurface strong brown to yellowish

brown (7.5 YR 4/1- 10YR5/6), fine sandy loam with weak sub-angular blocky structure [2, 3].

Ultisols are generally characterized by low fertility status with low chemical properties (pH,

CEC, organic matter) and low to very low total nitrogen, phosphorus and basic cations [1].

Acidic reactions and low activity clays are predominant in these soils, probably due to

high amounts of rain fall and other climatic conditions [3]. Clay fractions in these soils consist

almost entirely of well crystalized kaolinite, microcline, muscovite, sepiolite and some gibbsite

[1]

Ultisols of Awi are predominantly originate from sedimentary rock deposits. They are

crystalline in nature, easily weathered and deep under tropical humid conditions to depth greater

than 100 cm [4]. This is owing to the high rain fall intensity and adequate effective precipitation

resulting in Udic to marginally Ustic soil moisture regime but isohyperthermic in soil

temperature [5]. Soils derived from sandstones in Awi are cropped with oil palm, rubber and

gmalina) and arable crops namely: cassava, plantain and vegetables [6]. Presently,

industrialization, establishment of large plantations and increase in human population in this

area has exerted tremendous pressure on these soils. This study seeks to determine the

morphological and physico-chemical characteristics of soils derived from sandstone in Awi,

Akamkpa Local Government Area with the aim of suggesting appropriate management

measures for these soils.

2. MATERIALS AND METHODS

Location of the study

The study was carried out in Awi, Akamkpa Local Government Area of Cross River State,

Nigeria (Fig. 1). The study area lies between 5º00” and 5º51” N; 8º06” and 9º00” E). The

climate is tropical humid with annual rainfall of 2500 – 3000 mm, mean annual temperature of

26 – 31 ºC and relative humidly of 80-90 % at raining season [7].


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The soils of the area are derived from Awi sandstone formation consisting predominantly

of sand deposited by moving water or wind [4]. The topography was gently to strongly

undulating in some places. The original rainforest in the area has been tampered by human

activities.


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2. 1. Soil sampling

Three profile pits were dug along a toposeqence (crest, middle slope and lower slope) in

Awi, Akamkpa LGA. The coordinates for each profile pit location was recorded with the aid of

a Germain etrex (2000) global positioning system (GPS). The depth of the profile for sampling

was dictated by impenetrable layers or up to 200 cm, whichever was first encountered. The

profile description and sampling was done according to the FOA guidelines for soils profile

description. Undisturbed core cylinder soil samples were collected for bulk density

determination. Soil morphological features including: soil depth, colour, soil texture, structure

consistence, pores, boundary and miscellaneous were described in the field. Site environmental

features were also recorded. Soil samples were collected from each pedogenic horizons. The

soil samples were labeled and then transported to the laboratory for physicochemical analysis.

2. 2. Laboratory analysis

Soil samples were air-dried and sieved through a 2 mm mesh. Particle size analysis was

carried out by hydrometer method [8] using sodium hexametaphosphate (calgon) as the

dispersant. Soil pH was determined in soil water ratio 1:2.5 using a grass electrode pH meter.

Organic carbon was determined by the Walkley and Black method as out lined by [9] while

total nitrogen was by the micro-kjedahl digestion method [8]. Available phosphorus was

determined by Bray and Kurtz N 0.1 method as outlined by [10], exchangeable bases (Ca, Mg,

K and Na) were extracted with 1N NH4OAc at pH 7. Exchangeable potassium and sodium were

determined with a flame photometer while Ca and Mg were determined by the EDTA titration

method as outlined by [8, 11].

Exchangeable acidity was determined by titration method using 1N KCl extract as

outlined by lachat [11]. Cation Exchange Capacity was by the 1 M ammonium acetate

(NH4OAc) method at pH 7. Base saturation (%) was obtained by dividing the total

exchangeable bases (Ca, Mg, K and Na) by the effective cations exchange capacity.

3. RESULTS AND DISCUSSION

3. 1. Morphological Characteristics

The morphological characteristics of the three profiles on the different landscape

positions are presented in Table 1. The surface soils were brownish with Munsel notations of

7.5YR 3/2 and 10YR 3/3 while the subsurface soils yellowish brown, yellowish red to reddish

yellow. The dark brown for the surface soils indicates the presence of high humus content in

the soils while yellow and reddish subsurface indicate the presence of iron oxides. Similar

observations were reported by [12] and [2].

The soils were deep (>100 cm) and sandy clay to sandy clay loam texture in the

subsurface horizon; weak medium sub angular structure; slightly sticky-sticky and slightly

plastic-plastic consistency under wet condition. Profile depths of over 100 cm confirms the

assertion of [5], that soils overlay sandstone are deep. There are abundance of macro and micro

pores; many fine and medium roots as well as organisms such as termites, ants and worm casts

(Fig. 1A&B). Fragments of quartzite and weathered rocks with clear smooth boundaries of

horizon delineation are observed in the surface while gradual smooth to diffuse smooth

boundaries are noted in the subsurface [13].


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3. 2. Physical Characteristics

Particle size distribution (Table 2) indicates that the surface are sandy with sand content

of 59.3 to 70 % and 49.3 - 68.3 % (subsurface) resulting in an overall texture of sandy 1oamy

over sandy clay 1oam subsurface. Clay fraction (1-3) is varied from 7.7-8.7 % surface and 17.7-

37.7 % subsurface with mean of 8.2% and 27.7% respectively. The soils were well drained,

with clay content more than 20 % in the subsurface horizons. These soils can retain considerable

amount of water for crop production. The clay accumulation in the subsurface indicates

dominant pedogenic process of illuviation in the Bt horizons.

Fig. 1A. Profiles of soils developed on Awi sandstone formation in Akamkpa Local

Government Area of Cross River State-Nigeria.


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Fig. 1B. Profiles of soils developed on Awi sandstone formation in Akamkpa Local

Government Area of Cross River State-Nigeria.

Bulk density values increased with soils depth with a total surface and subsurface mean

values of 1.2 Mgm3 and 1.5 Mgm3 respectively. This value indicates that soils have no

mechanical impedance for plant roots and also have adequate aeration. The overall total

porosity of the soil varies from 22.0-28.6 % and 31.9 % for both surface and subsurface

respectively.


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Table 1. Morphological properties of soils developed on Awi Sandstone formation in

Akamkpa Local Government Area of Cross River State-Nigeria.

Note Texture: s = sand; c = clay: l = loam: Structure: 1 = weak; 2 = moderate; 3 = strong; f = fine; m = medium; c =

coarse; gr = granular; sbk = subangular blocky; Consistence; ns = non sticky, vf = very friable; ss = slightly sticky;

fi = firm; s = sticky; f = friable; Boundary: cw = clear wavy; cs = clea smooth; gs = gradual smooth.

Table 2. Physical properties of soils developed on Awi sandstone formation in Akamkpa

Local Government Area of Cross River State-Nigeria.

Note Texture class: sl = sand loam; scl = sandy clay loam


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This range of values typifies sandy loam material and can enhance easy movement of

moisture in the soils. These findings collaborates an earlier study of total porosities of these

soils by [12, 13] who noted that the soils were well granulated and have high moisture retention

for crop plants.

3. 3. Chemical Characteristics

The soils are generally strongly acid with average pH of 5.0 and 5.4 for the surface and

subsurface soil respectively (Table 3). The exchangeable acidity (sum of Al3+ and H+) values

(0.5 - 2.2 cmolkg-1) in the soils are comparable to the threshold value of 0.5-2.0 cmolkg-1 for a

productive soil as documented by [14, 15]. Organic carbon showed a decreasing trend with soil

depth. The Organic carbon varied from 14.4-38.1 g/kg and 2.4-18.6 g/kg with means of 26.3

g/kg and 10.5 g/kg in the surface and subsurface soils respectively. The result indicates a higher

level of organic carbon in the surface soils due to accumulation of organic matter in the surface

than in the subsurface soils. These results are in line with the finding of [15, 16,]. Total nitrogen

is varied from 1.2-3.3 g/kg and 0.1-1.5 g/kg in the subsurface soils with means of 2.3 g/kg and

0.8 g/kg respectively. The soils are rated as high to medium in total nitrogen content indicating

that the soils can respond positively to the application of organic and inorganic nitrogenous

fertilizers.

Table 3. Chemical properties of soils developed on Awi sandstone formation in Akamkpa

Local Government Area of Cross River State, Nigeria.

Available phosphorus is varied from 5.9-8.0 mg/kg and 4.1-8.3 mg/kg in the surface and

subsurface soils respectively with means of 7.0 mg/kg and 6.2 mg/kg. These values are

generally low, according to [16, 17] rating and these soils may require application of inorganic

phosphate fertilizers. Exchangeable cations Ca (1.0 - 1.2.8 cmolkg), Mg (0.1 - 2.8 cmo/kg), K

(0.07-0.11cmo/kg) and Na (0.06-0.09 cmo/kg) are generally low when compared with their

threshold values of 3.5, 1.0 and 0.1 cmol/kg [14, 17] for each cation respectively.


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This is an indication that the soils are highly leached and under advanced level of

weathering. Rapid leaching of basic cations has earlier been reported for soils developed from

sandstones in Mizoram North-East India [17]. The Effective Cation Exchange Capacity

(ECEC) is varied from 5.1-7.1 cmol/kg and is rated medium as most values are higher than 4.00

cmolkg-1 in most of the horizons (Table 3). The mean base saturation of 73.1 % and 46.1 %,

suggests that basic nutrients occur in available forms in soil solution for plant uptake despite

the low cations reserves in these soils.

3. 4. Classification

On the basis of morphological and physic-chemical properties, the soils are classified

under the USDA Soil Taxonomy and FAO-World Reference Base for soil Resources. The three

profiles have low base saturation (by summation of cations) of less than 50 % in the Bt horizon,

umbric epipedion (value of 3 or less, moist) and fit into the ultisols order of the USDA soil

Taxonomy. The profiles have Udic soil moisture regime and brown/brownish yellow kandic

horizons under humid tropical conditions therefore fit into the sub order of Udults. With Kandic

horizon, increasing in clay content with depth of 150 cm from the mineral soil surface, and

irregular decrease of organic carbon with depth, the three profiles are place in the Great group

Kandiudults and Typic kandiudults at the subgroup level. The soils are correlated with FAO-

UNESCO for WRB as Dystric Acrisols.

4. CONCLUSION

The investigation highlights the morphological and physico-chemical properties of soils

derived from sandstones in Awi, Akamkpa Local Government Area of Cross River State,

Nigeria. The soils are well developed, well drained with sandy loam texture. The soils are

characterized by very strongly acidic reactions, high organic carbon and nitrogen as well as low

available P and basic cations. The soils are classified as Typic Kandiudults and correlated as

dystric Acrisols. Therefore, the soil fertility management should focus on reducing leaching of

basic nutrients from the soils through mulching, planting of cover crops, crop rotation,

adoptions of zero tillage as well as application of liming materials to reduce the strong acidity

of the soils.

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