Physicochemical Properties as Affected by Concretionary Nodules of Oxic Rhodustalf of Southern Guinea Savanna Agroecological Zone of Nigeria

Physicochemical Properties as Affected by Concretionary Nodules of Oxic Rhodustalf of Southern Guinea Savanna Agroecological Zone of Nigeria

David Emmanuel^1,3, Adeyemo Adebayo Jonathan^1*, Oluwagbemi, Israel Adegbile¹, Omalle, Joy Afor⁴, Osakwe Uju Chinwe⁴, Adebayo Mathew Ayorinde², Ewulo Babatude Sunday¹

¹Department of Soil, Crop and Pest Management, Federal University of Technology, Akure, Nigeria.

²Department of Industrial Chemistry, Federal University of Technology, Akure, Nigeria.

³Agricultural and Rural Management Training Institute, Ilorin, Nigeria.

⁴Federal University Oye Ekiti, Ekiti, Nigeria.

*Corresponding Author

DOI: https://doi.org/10.51244/IJRSI.2024.1110059

Received: 10 October 2024; Accepted: 18 October 2024; Published: 20 November 2024

ABSTRACT

Diverse concretion types are prevalent across diverse soil types in the savanna region. However, its chemistry, mineralogy, profile, dimension, and abundance can significantly vary, influenced by the distinct weathering processes characteristic of each location. The accumulation of concretions in soil can have a considerable impact on its physical and chemical properties, especially at high concentrations. This effect largely depends on the chemical composition and mineralogy of the oxide components present [1]. Despite the potential significance of these effects, the influence of concretionary nodules on soil physicochemical properties remains underexplored. Existing studies are few and often lack detailed insights. Therefore, this study aims to investigate the physicochemical properties of soil influenced by concretionary nodules in the Oxic Rhodustalf of Southern Guinea Savannah, Nigeria. Results obtained from our analysis revealed interesting variations obtained. Three distinct textural classes were identified regarding physical properties: Sandy Loam, Sandy Clay Loam, and Loamy Sand. At various sites, the soil generally exhibited a slightly higher clay content (20.06 %) and sand content (74.04 %) compared to the concretions. However, the concretions had a higher silt content, at 7.34 %. Obbo Ile recorded the highest clay content (24.09 %) but the lowest silt and sand content among the locations. In contrast, Owu Isin had a significantly higher sand content (75.04 %). Clay content increased with depth, while sand content decreased. Although silt content generally increased, it dropped significantly after the 90-120 cm depth. Analysis of the chemical properties revealed significant variations (p < 0.05) for the parameters evaluated. The conductivity, pH in water, and CaCL₂ were higher in Soil than in concretions.   Similarly, the elements Na, K, Ca, and Mg also displayed higher values in soil. OM, SOC, Ex. Acidity and CEC except N (%) were significantly (p < 0.05) higher in soil than in concretions. The pH in H₂O was stable across depths and locations, with the highest value at 60-90 cm in Obbo Ile for soil and the lowest at the same depth in Owu Isin for concretions. pH measured with CaCl₂ mirrored this trend, peaking at 5.93. Conductivity decreased with depth, reaching its highest at 0-30 cm in Osi for soil. Base cations (Na, K, Ca, and Mg) were significantly higher in Obbo Ile and Osi compared to Owu Isin, with values consistently higher in soil than in concretions. Total nitrogen was highest (1.31 %) at 90-120 cm in Obbo Ile’s concretions. Soil organic carbon (SOC) peaked at 1.11 % at 0-30 cm in Owu Ile, and exchangeable acidity was highest at 90-120 cm there. Cation exchange capacity (CEC) was highest (0.35 meq/100 g) at 30-60 cm in Osi’s soil.

Keywords: Concretions, Nodules, Physical and Chemical properties, Guinea Savannah, Equilibrium Concentration.

INTRODUCTION

Concretionary nodules are integral components of the soil matrix, arising from the convergence of multiple, simultaneous geochemical and physical processes. These nodules are characterized by irregular and discontinuous growth patterns, with varying formation rates across different parts of the same nodule [2]. The internal structure of these nodules reflects a complex network of interactions within the soil system, embodying the cumulative effects of soil formation and environmental conditions [3]. Typically, nodules exhibit concentric, though not always continuous, layers that differ in their manganese (Mn) and iron (Fe) content, with the Mn-rich layers being bright or metallic and the Fe-rich layers appearing dull or black [4,5].

For instance, forming Fe-Mn concretions and nodules is a gradual process occurring over extended periods, closely tied to the pedogenetic development of soils. These structures’ shape, composition, and internal distribution patterns reveal the redox history of the soil environment [1]. Typically ranging in size from 1 to 15 cm in diameter [4,6], nodules are heavily influenced by the predominant source solutions from which they derive their composition [2].

Fluctuations in soil redox potential play a crucial role in the formation of these concretions. Under saturated conditions, iron and manganese oxides are reduced and dispersed throughout the soil. As the soil dries, oxygen levels increase, leading to the oxidation and reprecipitation of these elements, which line or occlude the soil’s pores [1]. The resultant concretions encapsulate a variety of soil matrix components, including skeletal grains, clay minerals, and pore spaces, which are cemented by the precipitated oxides. This process leads to a geochemical enrichment of iron and manganese oxides within the concretions, differentiating them from the surrounding soil matrix [7,8.9].

The distribution of nodules is highly variable, both regionally and locally, even within small-scale areas. For instance, in areas with a high overall abundance of nodules, coverage can vary significantly within a few hundred square meters, with some areas exhibiting no nodules and others having coverage exceeding two-thirds [10]. The spatial arrangement and frequency of these concretions within the soil matrix significantly impact soil porosity and its capacity to retain air and water. Dense accumulations of large concretions can disrupt pore networks and impede water infiltration, leading to increased surface runoff and exacerbating soil erosion, particularly on sloped surfaces [11]. In contrast, smaller, more evenly distributed concretions tend to have a less pronounced impact on soil porosity, thus mitigating negative effects on water movement and erosion.

Some studies highlight the structural differences between concretions and nodules, with concretions possessing well-defined concentric rings around a central point or plane, indicative of different pedogenetic processes [12,13]. Further research has identified ferrihydrite, goethite, or hematite as the primary mineral components of concretions, with variable amounts of aluminum substituting within the structure [14,15]. These minerals’ presence and specific compositions underscore the complexity of concretions and their significant influence on the chemical and physical properties of soils. Concretions from Greek Alfisols, for example, are enriched in thermodynamically unstable Fe oxides, further illustrating their dynamic role in soil processes [8].

MATERIALS & METHODS

A brief description of the Study Area

The research involved collecting soil samples using specialized equipment from various locations within the Southern Guinean savannah. Specifically, samples were collected from three communities in Kwara State: Owu Isin (latitude 08°16.58’N, longitude 05°55’6”E), Obbo-Ile (latitude 08°77.5’N, longitude 05°18’7”E), and Osi (latitude 07°3’6”N, longitude 05°08’7”E). These areas are located within the Southern Guinea savannah ecological zone of Nigeria.

Climate of the Study Area

The study areas experience a bimodal rainfall pattern, receiving approximately 1600 mm of precipitation, with peak periods in July and September and a dry spell in August. The mean daily maximum temperature ranges from 28°C to 34°C, while the mean daily minimum temperature fluctuates between 24°C and 26°C. Relative humidity is about 75% during the day and rises to 96% at night.

Land Use of the Study Areas

The study areas are predominantly characterized by arable and livestock farming as the main land-use types. Subsistence farming is prevalent in arable farming, involving intensive and continuous cultivation practices. The primary crops grown in these areas include sorghum, maize, cowpea, groundnuts, soybeans, and vegetables.

Map of the Study Area

Soil Mineralogy of the Study Areas

The study areas are defined by a combination of crystalline Precambrian basement complex rocks, including both metamorphic and igneous formations, along with sedimentary rocks [16]. In some locations, these rocks are overlain by substantial deposits of ferruginous tropical soils. The region is characterized by highly weathered red and yellowish-brown ferralsols in various spots. The soil profile typically consists of a moderately deep, reddish sandy clay loam with plinthite at depth, well-drained, and identified as Ferric Luvisol [17] and Oxic Rhodustalf [18]. Overall, the soil is a leached tropical ferruginous type, resting on a deeply weathered Precambrian basement complex, with ironstone gravels and ferruginized sandstone commonly present at higher elevations, which contribute to the formation of well-drained soils.

Soil Sampling Method

Soil samples were collected from three communities experiencing poor fertilizer efficacy. Farms with prominent concretionary nodules were selected within these communities. Soil profiles were excavated on these farms, and samples were taken at various depths: 0-30 cm, 30-60 cm, 60-90 cm, 90-120 cm, and 120-150 cm. Each profile was carefully delineated with horizon boundaries and measured. Comprehensive laboratory analyses were performed on samples from each genetic horizon, with triplicate samples for accuracy. The samples were air-dried, sieved, and stored for subsequent analysis of soil nutrient content and texture composition.

Separation of Concretionary Nodules

After air-drying and sieving through a 2-mm mesh, the soil samples were divided into concretionary nodules and fine soil fractions. Both fractions were then ground to a particle size of 2 mm or smaller and stored in plastic cups for further analysis.

Laboratory Analyses

To comprehensively evaluate the physical and chemical properties of concretionary nodules and fine soils, we employed internationally standardized analytical techniques. These analyses included particle size distribution, soil pH, organic carbon (OC) content, exchangeable bases (Ca²⁺, Mg²⁺, K⁺, and Na⁺), conductivity, exchangeable acidity, nitrogen (%), and cation exchange capacity (CEC).

Particle Size Distribution 

Soil particle size distribution was assessed using the modified Bouyoucos hydrometer method, as delineated by Gee and Or [19]. A 40 g soil sample was transferred to a beaker and mixed with 60 mL of water. To ensure thorough dispersion of soil particles and removal of organic matter, 100 mL of a 5% sodium hexametaphosphate (Calgon) solution was introduced. The mixture was allowed to stand for approximately 10 minutes, followed by vigorous agitation with a mechanical stirrer for 30 minutes. The resulting suspension was carefully decanted into a graduated sedimentation cylinder, with distilled water used to rinse the beaker and adjust the cylinder volume to 1 liter. The temperature of the suspension was recorded upon reaching equilibrium. The suspension was then homogenized using a plunger, and hydrometer readings were obtained at 5 minutes and 5 hours to determine the clay and silt fractions. Following the final hydrometer measurement, the suspension was filtered through a 45-µm sieve. The retained particles were washed with distilled water, dried in an oven at 105 °C for 24 hours, and classified as the sand fraction. Blank hydrometer readings of the sodium hexametaphosphate solution were also recorded at equivalent intervals. The particle size distribution was subsequently computed using the provided formulas.

The temperature effects on the soil particles were accounted for using the relation provided by Day (1966). Thus, for every 1-^oC rise in temperature above 19.5 ^oC, there is an increase of 0.3^oC in the density of the particles in suspension.

Correction for temperature = blank hydrometer reading – increase in weight of particles.

Soil pH and Electrical Conductivity

The soil pH was assessed using a glass electrode pH meter, as per the method delineated by Hendershot and Lavkulich [20]. A soil-to-water ratio of 1:1 was employed, wherein 20 g of soil was placed in a 50 mL beaker, and 20 mL of deionized water was added. The suspension was agitated for 30 minutes to ensure thorough mixing and then left to equilibrate at ambient temperature. The pH meter was pre-calibrated with standard buffer solutions of pH 4.0 and 7.0 to ensure accuracy. The calibrated pH electrode was subsequently inserted into the supernatant to obtain the pH measurement of the soil sample. In addition, the electrical conductivity (EC) was determined using the same suspension. After calibrating the conductivity meter, the electrode was immersed in the supernatant to measure the EC, reflecting the soil’s soluble ion concentration.

Exchangeable Cations 

A 5 g soil sample was precisely measured and placed into an extraction bottle. To extract exchangeable cations, 50 mL of a 1M ammonium acetate (NH₄OAc) solution, buffered to pH 7, was added to the sample. The extraction bottle was then subjected to vigorous agitation on a mechanical shaker for one hour, ensuring thorough interaction between the soil and the extractant. Post-extraction, the suspension was filtered using Whatman No. 42 filter paper to separate the solid and liquid phases. The resultant filtrate was collected in clean, labeled containers for analysis. The exchangeable calcium and magnesium concentrations in the filtrate were quantitatively determined using an Atomic Absorption Spectrometer (AAS), offering high sensitivity and specificity for these elements.

Potassium (K) determination 

The flame photometer was calibrated such that a concentration of 10 mg/kg of potassium (K) produced a full-scale reading of 100. Following calibration, the flame photometer was utilized to determine the potassium concentration in a 10 mL sample. The resulting data were then used to calculate the total potassium content in the soil, as outlined in the formula below:

Where:

W = Flame photometer reading for K (μg/mL)

Z = Charge on K

H = Atomic mass of K

Sodium (Na) determination 

The flame photometer was calibrated such that a concentration of 10 mg/kg of sodium (Na) resulted in a full-scale deflection of 100. After calibration, the photometer was used to measure the sodium concentration in a 10 mL aliquot. The obtained result was then applied to calculate the total amount of sodium present in the soil, as demonstrated by the formula below.

Where:

Y = Flame photometer reading for Sodium (μg/mL)

D = Charge on Na

F = Atomic mass of Na

Calcium (Ca) Determination

Calcium was measured from the filtered solution using an Atomic Absorption Spectrophotometer (AAS). The instrument was calibrated with standard calcium solutions containing concentrations of 2, 6, and 10 μg/mL at a wavelength of 422.7 nm, with a slit width of 0.07 nm and a current of 10 A. The values obtained were then used in the formula below to estimate the amount of calcium present in the soil sample(s):

Where:

A = AAS reading (μg/mL)

B = Charge on Ca

C = Atomic mass of Ca

Magnesium (Mg) Determination

Magnesium (Mg) was determined from the filtered solution using the Atomic Absorption Spectrophotometer (AAS). The instrument was calibrated with standard magnesium solutions of 0.2, 0.6, and 1.0 μg/mL, at a wavelength of 422.7 nm, with a slit width of 0.07 nm and a current of 10 A. The obtained readings were then used in the formula below to estimate the amount of magnesium present in the soil sample(s):

Where:

M = AAS reading (μg/mL)

G = Charge on Mg

Q = Atomic mass of Mg

Exchangeable Acidity (H⁺ and Al³⁺)

Aluminium and hydrogen ions were extracted from soil samples using 1 M KCl, as described by Thomas [21]. Approximately 10 g of soil was transferred to a 100 mL extraction bottle, and 50 mL of 1 M KCl solution was added. The bottle was placed on a mechanical shaker and agitated for 30 minutes. Following agitation, the soil suspension was filtered through Whatman No. 40 filter paper into a clean, empty bottle. A 25 mL aliquot of the filtrate was pipetted into a 100 mL conical flask, and 2-3 drops of phenolphthalein indicator were added. The solution was titrated with 0.01 M NaOH until a persistent pink endpoint was reached, and this titre was recorded as the combined amount of H+ and Al³⁺. To measure aluminium specifically, 10 mL of NaF was added to the solution at the endpoint, and the solution was then back-titrated with 0.01 M HCl until the endpoint became colorless. The titre value from this back-titration was recorded as the amount of Al³⁺.

Effective cation exchange capacity (ECEC) and base saturation 

The effective cation exchange capacity is equal to the sum of the exchangeable (Ca²⁺,  Mg²⁺, Na⁺, K⁺, H⁺, and Al^3+. (i.e., ECEC = Ca²⁺ + Mg²⁺ + Na⁺ + K⁺ + H⁺ + Al³⁺) ……… (9)

Base saturation was calculated as the sum of bases (Ca, K, Mg, and Na) expressed as a percentage of effective CEC.

Statistical Analysis

Significant differences in physicochemical properties of soil and bulk soil with concretions, sieved soil without concretions, and the concretions alone were investigated using an ANOVA. Statistical analyses were conducted utilizing Excel 2007 [22] and SAS Statistical Software version 9 (2002).

RESULT

Physical properties of the soils under the influence of concretion nodules in the study area.

Main Effect of Concretionary Nodules on Soil Physical Properties in the Study Areas

The effect of concretionary nodules on soil physical properties at two distinct sites is detailed in Table 1. It shows that the soil has higher clay (20.06 %) and sand (74.04 %) content compared to the concretions, with significant differences between the means. In contrast, the silt content is significantly higher in the concretion sites (7.34 %) than in the soil sites (5.97 %). Despite these differences, both the soils and concretions share the same textural classification of Sandy Loam.

Main Effect of Location on Soil Physical Properties in the Study Areas

All three locations were classified under the same textural class, yet they exhibited significant differences in soil particle proportions, as shown in Table 2. Obbo Ile had the highest clay content at 24.09 %, followed by Owu Isin at 18.89 % and Osi at 18.86 %. Osi had the highest silt content at 8.09 %, whereas Obbo Ile had the lowest silt content at 5.81 %. Additionally, Osi had the lowest sand content at 70.10 %, while Owu Isin recorded the highest sand content at 75.04 %.

Main Effect of Soil Depth on Soil Physical Properties in the Study Areas

Table 3 assesses the main effect of soil depth on soil physical characteristics. Soil depths of 0-30 cm, 30-60 cm, and 60-90 cm all exhibited the same textural class. However, at depths of 90-120 cm and 120-150 cm, the textural class shifted to Sandy Clay Loam. Significant variations in soil particle proportions were observed with depth. The 90-120 cm depth had the highest clay content at 22.47 %, while the 0-30 cm depth had the lowest clay content at 16.25 %. A similar trend was noted for silt, with the highest content at 90-120 cm (10.13 %) and the lowest at 0-30 cm (5.17 %). Conversely, the sand content was highest at 0-30 cm (78.58 %) and lowest at 90-120 cm (67.40 %).

Interaction Effect of Farm Sites and Location on Soil Physical Properties in the Study Areas

The interaction effect of farm site and location on the study area is summarized in Table 4. All sites, except Obbo Ile at the concretion sites, exhibited the same textural class of Sandy Loam. However, there were significant differences in the proportions of soil particles. Obbo Ile had the highest clay content at both soil (22.94 %) and concretion (25.20 %) sites, while the lowest clay content was observed at the concretion sites in Owu Osin (14.73 %). The highest silt content was recorded in Osi at the concretion sites, which was 3.61% higher than the highest silt value recorded at the soil sites in Obbo Ile (6.44 %). Conversely, the lowest silt content was found in Obbo Ile at the concretion sites (5.19 %). Regarding sand content, the highest values were recorded in Owu Osin at the soil sites (78.48 %), followed by the same location at concretion sites. Overall, the lowest sand content was recorded in Obbo Ile, with a value of 69.61 %.

Interaction Effect of Sites and Soil depth on physical properties in the Study Areas

The interaction effects of sites and soil depth, as detailed in Table 5, revealed significant differences. At soil sites, the depths of 0-30 cm, 30-60 cm, and 60-90 cm all exhibited the same textural class of Sandy Loam, whereas the depths of 90-120 cm and 120-150 cm were classified as Sandy Clay Loam. Concretion sites generally followed a similar textural classification at all depths, except for the 120-150 cm depth, which was also classified as Sandy Clay Loam.

Significant variations were observed in the proportions of soil particles. The highest clay content was recorded at the soil sites with a depth of 120-150 cm, reaching 25.58 %. In contrast, the lowest clay content was found at the 30-60 cm depth at both soil (15.49 %) and concretion (15.46 %) sites. The highest silt content of 11.61 % was observed at the 60-90 cm depth at concretion sites, followed by 7.20 % and 7.27 % at the 30-60 cm depth at soil and concretion sites, respectively. The lowest silt content of 4.92 % was recorded at the 90-120 cm depth at soil sites. Regarding sand content, the highest values were observed at the 0-30 cm, 30-60 cm, and 60-90 cm depths at soil sites (77.47 %, 77.31 %, and 78.71 %, respectively) and at the 30-60 cm and 90-120 cm depths at concretion sites (77.27 % and 73.51 %, respectively), with the highest value of 79.71 % recorded at the 0-30 cm depth.

Interaction Effect of Location and Soil depth on soil physical properties in the Study Areas

The interaction effect of site and location on soil physical properties, as outlined in Table 6, revealed significant differences. In Owu Isin, the soil texture class consistently remained Sandy Loam across all depths. In contrast, Obbo Ile displayed a change in texture: Sandy Loam at depths of 0-30 cm and 30-60 cm, transitioning to Sandy Clay at depths of 60-90 cm, 90-120 cm, and 120-150 cm. Obbo Ile had the highest clay content at 32.30 % at the 120-150 cm depth. In Osi, the silt content was notably higher at 15.40 % at 30-60 cm, whereas Obbo Ile had lower silt content at depths of 90-120 cm and 120-150 cm, with values of 62.23 % and 61.05 %, respectively. The highest silt content of 79.76 % was recorded at the 0-30 cm depth in Osi.

Interaction Effect of Farm Site, Location, and Soil depth on soil physical properties in the Study Area.

Table 7 reveals significant interaction effects of site, location, and depth on soil physical properties. Except for Obbo Ile, where the textural class remained consistent between soil and concretions, variations were observed across other locations and sites. Clay content was higher at deeper depths (90-120 cm and 120-150 cm) across all locations, with the highest value of 34.78 % recorded at a depth of 120-150 cm in concretions. Silt content showed variable trends with depth in both soil and concretions at all three locations. The highest silt content of 10.13 % was found in Osi at 90-120 cm in concretions, while the lowest, at 2.64 %, was measured at a depth of 0-30 cm in Obbo Ile. Conversely, sand content was generally higher than both silt and clay across the study area. The highest sand proportion of 84.57 % was recorded at 0-30 cm in both soil and concretions in Obbo Ile, whereas the lowest sand proportion of 60.78 % was observed at 90-120 cm in soil at Obbo Ile.

Chemical properties of the soils under the influence of concretion nodule

Main Effect of Concretionary Nodules on Soil Chemical Properties in the Study Areas

The analysis of soil and concretions revealed notable differences in chemical properties. Soil sites exhibited significantly higher values for pH in water (6.51) and pH in CaCl₂ (5.08), as well as electrical conductivity (14.47 µS/cm), compared to the concretions. Conversely, base cations such as sodium (0.65 cmol/kg), potassium (0.60 cmol/kg), calcium (0.60 cmol/kg), and magnesium (0.74 cmol/kg) were found in greater concentrations in the concretions than in the soil. Organic matter content was 64 % higher in soils compared to concretions. Additionally, soil organic carbon, cation exchange capacity (3.01 meq/100 g), and exchangeable acidity (0.42 meq/100 g) were higher in soils. In contrast, nitrogen levels were higher in the concretions, with a concentration of 0.62 % (Table 8).

Main Effect of Location on Soil Chemical Properties in the Study Areas

The chemical properties of the soil across different locations, as detailed in Table 9, displayed significant variations. Osi recorded the highest pH values in both H₂O (6.53) and CaCl₂ (5.42). Electrical conductivity and soil organic matter concentrations increased from Owu Isin, which had the lowest values, to Osi, which had the highest. Total nitrogen levels were lowest in Owu Isin (0.55 %) and highest in Obbo Ile (0.72 %). Base cations sodium (0.60 cmol/kg) and magnesium (0.64 cmol/kg) were notably higher in Osi, while Owu Isin had lower values for these cations (0.38 cmol/kg for sodium and 0.40 cmol/kg for magnesium). Conversely, potassium (0.60 cmol/kg) and calcium (0.59 cmol/kg) were at their highest in Obbo Ile, whereas Owu Isin had the lowest levels of potassium (0.25 cmol/kg) and calcium (0.29 cmol/kg). Soil organic carbon (SOC) was highest in Osi (0.55 %) and lowest in Owu Isin (0.45 %). Exchangeable acidity followed a similar trend to SOC, with lower values in Obbo Ile (0.36 %) and higher values at the other two locations.

Main Effect of Soil depth on soil Chemical Properties in the Study Areas

The impact of soil depth on chemical properties, as shown in Table 10, reveals notable variations. Both conductivity and pH in CaCl₂ decreased with increasing depth throughout the soil profile. The behavior of base cations (Na, K, Ca, Mg) and organic matter (OM) exhibited inconsistent patterns, alternating between increases and decreases across different depths. Nitrogen percentage, soil organic carbon (SOC), and exchangeable acidity initially decreased but then increased at mid-depths before declining again at greater depths. Cation exchange capacity (CEC) followed a similar downward trend, though differences among treatment means were not statistically significant. Overall, Na, K, Ca, Mg, OM, nitrogen, and SOC were more concentrated in the top 0-30 cm and 30-60 cm layers compared to deeper layers.Top of FormBottom of Form

Interaction Effect of Sites and Location on Soil Chemical Properties in the Study Areas

The interaction effects of sites and locations on various soil properties revealed significant differences. As shown in Table 11, the pH values for both H₂O and CaCl₂ peaked at Obbo Ile with values of 6.69 and 5.53, respectively. In contrast, lower pH values were found at Owu Isin, with pH H₂O at 5.68 and pH CaCl₂ at 4.12 in concretion sites. Conductivity was notably higher in Obbo Ile and Osi, with the highest value (17.7 µS/cm) recorded in Osi soil samples. For base cations, Na, K, and Ca reached their maximum concentrations in Obbo Ile soil samples (0.82, 0.82, and 0.94, respectively), while the lowest values for Na (0.34) were found in Owu Isin soil samples, and for K (0.20) in Owu Isin, and Ca (0.14) in Osi, all in concretion samples. Magnesium levels were lowest in Obbo Ile concretion samples (0.25). Organic matter (OM), soil organic carbon (SOC), and cation exchange capacity (CEC) were highest in Obbo Ile soil samples, with values of 1.25 %, 0.73 %, and 3.99 meq/100, respectively. OM and SOC were at their lowest in Owu Isin concretion samples (0.41 % and 0.24 %, respectively), while CEC was lowest in Osi concretion samples (1.58 meq/100). Total nitrogen (N) was highest in Obbo Ile concretion samples (0.81 %), and lowest in Osi. Exchangeable acidity was highest in Owu Isin soil samples (0.46), with higher values (0.36) in concretion samples.

Interaction Effect of Sites and Soil depth on chemical properties in the Study Areas

Table 12 highlights the significant effects of site, soil depth, and their interactions on soil chemical properties. A notable interaction (P < 0.05) between site and location was observed. For pH in H₂O, values decreased with increasing depth in soil samples but increased in concretions. The highest pH values were recorded at 60-90 cm depth in soil, while the lowest were at 0-30 cm in concretions. A similar trend was noted for pH in CaCl₂, which showed a pronounced decline with depth in both soil and concretions. Conductivity was higher at depths of 0-30 cm and 30-60 cm for both soil and concretions, with soil exhibiting values of 26.50 µS/cm and 15.83 µS/cm, respectively, and concretions showing 23.67 µS/cm and 17.83 µS/cm. Significant differences (P < 0.05) in base cations were observed across sites and depths. Sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) reached their highest values (0.78, 0.73, 0.69, and 0.85, respectively) in soil. In contrast, the lowest values for these cations were found in concretions, with Na (0.26) and K (0.25) at 120-150 cm depth, Ca (0.21) at 0-30 cm and 60-90 cm, and Mg (0.27) at 90-120 cm.

Soil organic matter (SOM) and soil organic carbon (SOC) decreased with depth, with the highest values (1.51 % for SOM and 0.88 % for SOC) at 0-30 cm and 60-90 cm in soil, and the lowest (0.36 % and 0.21 %, respectively) at 120-150 cm in concretions. Total nitrogen showed variable trends across depths in both soil and concretions, peaking at 0.86 % at 90-120 cm and dropping to 0.41 % at 120-150 cm in concretions. Cation Exchange Capacity (CEC) was significantly higher in soil, ranging from 3.55 to 2.76 meq/100, compared to concretions, which ranged from 1.97 to 1.69 meq/100.

Interaction Effect of Location and depth on soil chemical properties in the Study Areas

Significant interactions between site and soil depth on soil chemical properties were observed in the study area. A notable finding is the stable pH in H₂O with increasing depth across all locations. In contrast, pH measured with CaCl₂ consistently declined with depth in both soil and concretions at Owu Isin, Obbo Ile, and Osi (Table 13). Soil conductivity was markedly higher at depths of 0-30 cm, 30-60 cm, and 120-150 cm in Osi compared to other locations, with respective values of 33.75 µS/cm, 23.00 µS/cm, and 12.50 µS/cm. Significant differences (P < 0.05) were found for base cations across locations and depths, excluding sodium (Na). Potassium (K) displayed a decreasing trend with depth, peaking at 0.71 at 30-60 cm in Osi and falling to 0.17 at 120-150 cm in Owu Isin. Calcium (Ca) decreased in Owu Ile and Osi but increased in Obbo Ile, with the highest values (0.73) recorded at 120-150 cm in Obbo Ile and the lowest at 90-120 cm in Owu Ile. Sodium (Na) and magnesium (Mg) were highest at depths of 30-60 cm and 0-30 cm, respectively, in Osi, while their lowest values (0.19 for Na and 0.36 for Mg) were recorded at 120-150 cm in Owu Isin.

Both Soil Organic Matter (SOM) and Soil Organic Carbon (SOC) exhibited decreasing trends with increasing depth. Higher values were observed at 0-30 cm and 30-60 cm for SOM, and at 60-90 cm for SOC. Total nitrogen levels peaked at 0.99 % at 90-120 cm in Obbo Ile. Exchangeable acidity was highest at 0.72 at 90-120 cm in Owu Isin and lowest at 0.25 at 30-60 cm in Obbo Ile. The Cation Exchange Capacity (CEC) was highest at 3.28 meq/100 at 30-60 cm in Osi. The interaction between site and soil depth highlights the need for tailored soil management practices. The stable pH in H₂O with increasing depth, contrasted with the declining pH in CaCl₂, indicates varying chemical dynamics within soil profiles. Higher conductivity in Osi at specific depths suggests differences in soil composition and moisture content. The variations in base cations, organic matter, and nitrogen levels across sites and depths emphasize the importance of localized soil analysis for effective agricultural and land management.

Interaction Effect of Sites by Location by Soil depth on soil chemical properties in the Study Areas

The study revealed significant interactions between farm site, location, and soil depth, impacting various soil chemical properties (Table 14). The pH in H₂O remained relatively stable across different depths and locations for both soil and concretions. The highest pH in H₂O was found at a depth of 60-90 cm in Obbo Ile for soil, while the lowest was at the same depth in Owu Isin for concretions. Similarly, pH measured with CaCl₂ followed a comparable trend, with elevated values observed at the same depth and location for both soil and concretions, reaching up to 5.93. Conductivity exhibited a decreasing trend with increasing depth, peaking at 0-30 cm in Osi for soil. In terms of base cations, Na, K, Ca, and Mg were significantly higher (P<0.05) in Obbo Ile and Osi compared to Owu Isin for soil, with minor differences between locations. These base cations were consistently higher in soil compared to concretions.

Total nitrogen, soil organic carbon (SOC), exchangeable acidity, and cation exchange capacity (CEC) showed variable trends, with both increases and decreases depending on the depth and location. Total nitrogen was highest (1.31 %) at 90-120 cm in concretions at Obbo Ile. SOC reached its peak at 1.11 % at 0-30 cm in Owu Ile for soil, while exchangeable acidity was highest at 90-120 cm at the same location. CEC values were highest (0.35 meq/100) at 30-60 cm in Osi for soil.

DISCUSSION

Enhancing agricultural productivity requires the optimization of crop nutrition, which is closely tied to the chemical, physical, and biological processes occurring in the soil. These processes are influenced by factors such as mineral composition, organic content, fertilization practices, and soil management strategies [23,24]. However, in the Nigerian Guinean Savannah, these efforts are often undermined by widespread soil degradation, largely due to unsustainable land use practices and the impacts of climate stress [25,26,27,28]. Exacerbating these challenges, the highly weathered tropical soils in this region are distinguished by the presence of abundant iron (Fe) and aluminum (Al) oxides, hydroxides, and oxyhydroxides [29,30,31]. These compounds often manifest as concretionary nodules, which are prevalent in such soils [32,33].

The distribution, nature, and abundance of these concretions play a crucial role in determining the soil’s nutrient status [29,34]. Concretions are known for their diverse characteristics, which provide valuable insights into their origins and formation processes. These processes can be diagenetic, epigenetic, metamorphic, metasomatic, sedimentary-hydrothermal, or hydrothermal. Concretions can vary in composition such as carbonate, siliceous, phosphoritic, baritic, sideritic, and ferromanganese. In terms of texture, they can range from simple to composite, dense homogeneous, or bedded forms [35,36]. Furthermore, their shapes vary widely, with forms such as globular, flattened, lenticular, columnar, and conical being commonly observed [Dietzel, 2000; 38]. Previous studies have documented a variety of morphological forms for soil concretions and nodules, including spherical, oval, subangular, tubular, and irregular shapes [8,39,40,41,42]. These structures vary in size, typically ranging from 0.25 mm to 4 cm. The mineralogical composition of these concretions is often reflected in their coloration, for instance, darker hues are associated with higher concentrations of manganese (Mn), whereas red, yellow, orange, or brown hues with elevated chroma values are indicative of increased iron (Fe) oxide content [7,43].

Physical Properties

Ferruginous and ferruginous-manganese concretions, for instance, differ significantly from the properties of the host soil horizons, characterized by higher particle density, reduced moisture, lower porosity, and the presence of a significant volume of extremely small pores [44]. Concretionary nodules can have several effects on soil properties. These effects can vary depending on the organization and dispensation of the nodules within the soil profile. Our analysis revealed a noticeable disparity in soil texture and concretions across different depths and locations. While the soil exhibited a slightly higher sand content at 74.04% compared to 73.57% in concretions, this variation was not statistically significant (P < 0.05). The clay content was 20.06% in the soil and 19.16% in concretions, both classified as Sandy Loam (SL). This is consistent with Abekoe & Tiessen’s [45] research, which found that soils from upper slopes exhibited higher contents of lateritic nodules and sandy loam textures, while soils from lower slopes had fewer nodules and sandy or silt loam textures. Regardless of location differences, the highest clay content (18.89%) and sand content (75.04%) were discovered in Owu Isin, while Osi had the highest silt content (8.09%). The impact of concretions on soil physical properties is often contingent upon the soil’s inherent texture and clay mineralogy. In coarse-textured soils, such as sands, concretions tend to have a minimal effect on porosity and drainage due to the naturally large pore spaces [46]. However, in fine-textured soils with higher clay content, the presence of concretions can further restrict pore space and exacerbate drainage issues.

Chemical Properties

(pH, conductivity, Na, K, Ca, Mg, Ex. Acidity, CEC, N (%), and SOC)

The impact of concretions on soil chemical properties was analyzed comprehensively across various locations and depths. The analysis revealed that concretions contributed to more acidic conditions in the soil, with slightly lower pH values than soils, potentially affecting nutrient availability and soil biological activity. This coincides with the findings of Abdu & Emmanuel [47], who observed that the concretionary nodules were slightly acidic and fairly consistent across all fields, ranging from pH 4.9 to 5.9. These soils are moderate to highly acidic due to the removal of bases, leading to an appreciable accumulation of sesquioxide minerals, such as iron and aluminum oxides, as well as significant amounts of lateritic concretions or nodules [23] (Asomaning et al,, 2018; Ahmed et al,, 2017; Abdu et al,, 2012).

Soils exhibited higher electrical conductivity (14.47 µS/cm) compared to concretions (13.80 µS/cm), indicating greater retention of soluble salts, which is essential for nutrient mobility and plant uptake. Additionally, soils had higher levels of exchangeable bases and a significantly greater cation exchange capacity (3.01 meq/100g) compared to concretions (1.65 meq/100g). This finding contradicts previous studies, which characterized these soils as having low native fertility due to low nutrient content, low CEC, and high phosphorus retention by oxide minerals [48]. Soil organic carbon was higher in soil than in concretions with a significant difference (P < 0.05). Abdu & Emmanuel [47] reported similar findings, noting that sieved soils without concretion had more organic carbon content than soils with concretions. Miltner and Zech [49] observed that elevated temperatures can lead to a substantial reduction in organic carbon, with up to 40% of the total organic carbon being released as CO₂, and can cause significant changes in the composition of organic matter. The organic matter content was significantly higher in soils (1.20%) compared to concretions (0.62%), highlighting the soil’s superior capacity for maintaining fertility and structure. Additionally, soils demonstrated slightly elevated levels of exchangeable acidity. This observation is consistent with the work of Potter-McIntyre et al, [50], who emphasized that concretions often form within organic-rich environments, where the role of organic matter in guiding mineral precipitation is well-established [51,52,53].

CONCLUSION

The investigation into soil texture and concretions across varying depths and locations provides valuable insights into their influence on soil physicochemical properties. While the observed differences in sand and clay content between the soil and concretions were not statistically significant, the role of concretions in soil structure and functionality remains critical. Concretions are easily identified in soil profiles [54], and their distinct morphological characteristics such as shape, color, and size underscore their heterogeneity compared to surrounding soil materials.

Their distinct morphological features, such as variability in shape, color, and size, highlight the heterogeneity of concretions compared to the surrounding soil matrix. This heterogeneity, along with the potential for recrystallization influenced by climatic factors like humidification [55], suggests that concretions play a complex and significant role in shaping soil physicochemical properties. Given these findings, further research is necessary to expand our understanding of the morphology and fabric characteristics of concretionary nodules and their broader implications for soil health and management.

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Table1. Main Effect of Concretionary Nodules on soil Physical Properties in the Study Areas

Farm Sites	%Clay	%Silt	%Sand	Textural Class
soil	20.06a	5.97b	74.04a	SL
concretion	19.16b	7.34a	73.57b	SL

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test

Table 2. Main Effect of Location on soil Physical Properties in the Study Areas

Locations	Clay	Silt	Sand	Textural Class
	—————%——————-
Owu Isin	18.89c	6.07b	75.04a	SL
Obbo Ile	24.09a	5.81c	70.10c	SL
Osi	18.86b	8.09a	73.05b	SL

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test SL-Sandy Loam

Table3. Main Effect of Soil Depth on soil Physical Properties in the Study Areas

Soil depth	Clay	Silt	Sand	Textural Class
	——————–%—————-
0-30	16.25e	5.17e	78.58a	SL
30-60	16.40d	5.52d	78.08b	SL
60-90	17.75c	6.84b	75.41c	SL
90-120	22.47b	10.13a	67.40e	SCL
120-150	25.17a	5.62c	69.21d	SCL

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test SL-Sandy Loam SCL-Sandy Clay Loam

Table 4. Interaction Effect of Farm Sites and Location on soil physical properties in the Study Areas

Farm Site	Location	Clay	Silt	Sand	Textural Class
		————– %————–
Soil	Owu Isin	17.05e	5.35e	77.60b	SL
	Obbo Ile	22.94b	6.44c	70.62e	SL
	Osi	20.15c	6.13d	73.72c	SL
concretion	Owu Isin	14.73f	6.79b	78.48a	SL
	Obbo Ile	25.20a	5.19f	69.61f	SCL
	Osi	17.56d	10.05a	72.39d	SL

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test SL-Sandy Loam SCL-Sandy Clay Loam

Table5. Interaction Effect of Sites and Soil depth on physical properties in the Study Areas

Farm Site	Depth	Clay	Silt	Sand	Textural Class
	cm	———— % —————
Soil	0-30	16.71g	5.82g	77.47c	SL
	30-60	15.49i	7.20d	77.31d	SL
	60-90	17.51f	3.78j	78.71b	SL
	90-120	25.01c	4.42i	70.57f	SCL
	120-150	25.58a	8.64b	65.78i	SCL
Concretion	0-30	15.76h	4.53h	79.71a	SL
	30-60	15.46i	7.27c	77.27d	SL
	60-90	19.36e	11.61a	69.03g	SL
	90-120	20.01d	6.48f	73.51e	SL
	120-150	25.17b	6.83e	68.00h	SCL

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test SL-Sandy Loam SCL-Sandy Clay Loam

Table 6. Interaction Effect of Location and Soil depth on soil physical properties in the Study Areas

Location	Soil depth	Clay	Silt	Sand	Textural Class
	cm	————– %—————
Owu Isin	0-30	15.35n	6.29m	78.36a	SL
	30-60	15.99j	8.91b	75.10i	SL
	60-90	15.60l	7.40c	77.00f	SL
	90-120	18.63h	5.78k	75.59g	SL
	120-150	16.81i	4.25m	78.94d	SL
Obbo Ile	0-30	15.64l	4.71l	79.65c	SL
	30-60	18.82g	5.86h	75.32h	SL
	60-90	21.87d	6.81d	71.32k	SCL
	90-120	31.70b	6.07g	62.23n	SCL
	120-150	32.30a	6.65j	61.05o	SCL
Osi	0-30	13.77m	6.47e	79.76b	SL
	30-60	19.68f	15.40a	64.92m	SL
	60-90	15.61k	6.30f	78.09e	SL
	90-120	20.76e	6.52e	72.72j	SL
	120-150	24.36c	5.75i	69.89l	SCL

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test SL-Sandy Loam SCL-Sandy Clay Loam

Table 7. Interaction Effect of farm Site, Location and Soil depth on soil physical properties in the Study Area.

Farm Sites	Locations	Soil depth	% Clay	% Silt	% Sand	Textural class
		cm	—————– %————
Soil	Owu Isin	0-30	16.76n	5.30	77.94c	SL
		30-60	16.27q	9.38d	74.35m	SL
		60-90	15.77s	7.48gh	76.75i	SL
		90-120	19.52k	3.40	77.03gh	SL
		120-150	19.80j	3.17	77.03h	SL
	Obbo Ile	0-30	18.53n	6.77mn	74.70l	SL
		30-60	18.94l	4.86s	76.20j	SL
		60-90	14.86	6.87l	78.27f	SL
		90-120	32.84b	7.08k	60.08	SCL
		120-150	29.77d	6.65o	63.58t	SCL
	Osi	0-30	17.86o	7.39hi	74.75l	SL
		30-60	13.60	3.31	83.09c	LS
		60-90	15.69r	7.25j	77.06gh	SL
		90-120	27.63f	9.48c	62.89	SCL
		120-150	25.68g	3.21	71.11n	SL
Concretion	Owu Isin	0-30	10.94	5.74q	83.32b	LS
		30-60	13.77	5.33q	80.90d	LS
		60-90	15.55t	7.34i	77.11g	SL
		90-120	15.70s	8.45e	75.85k	SL
		120-150	17.67p	7.55g	74.78l	SL
	Obbo Ile	0-30	12.76	2.67	84.57a	LS
		30-60	18.84m	6.85lm	74.31m	SL
		60-90	28.81e	6.74n	64.45r	SCL
		90-120	30.64c	5.06b	64.30s	SCL
		120-150	34.78a	4.65t	60.57	SCL
	Osi	0-30	23.67h	5.66p	70.67o	SCL
		30-60	13.78	9.63b	76.59i	SL
		60-90	15.52t	5.35q	79.13e	SL
		90-120	21.63	11.32a	67.05q	SCL
		120-150	23.05i	8.28f	68.67p	SCL

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test SL-Sandy Loam SCL-Sandy Clay Loam LS- Loamy Sand

Table 8. Main Effect of Concretionary Nodules on soil Chemical Properties in the Study Areas

Sites

pH water

pH CaCl2

Conductivity (µscm)

Na

K

Ca

Mg

OM

N (%)

SOC (%)

Ex. Acidity

CEC (meq/100)

soil

6.51a

5.08a

14.47a

0.65a

0.60a

0.60a

0.74a

1.20a

0.57b

0.70a

0.42a

3.01a

concretion

6.17b

4.87b

13.80b

0.38b

0.32b

0.24b

0.32b

0.56b

0.62a

0.32b

0.40b

1.65b

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test

Table 9. Main Effect of Location on Soil Chemical Properties in the Study Areas

Locations

pH water

pH CaCl2

Conductivity

Na

K

Ca

Mg

OM

N (%)

SOC (%)

Ex. Acidity

CEC

µscm

————- Cmol/kg—————-

———- % ———-

Cmol/kg

meq/100

Owu Isin

6.02c

4.41c

10.95c

0.38b

0.25c

0.29c

0.40c

0.78c

0.55b

0.45c

0.43a

1.95b

Obbo Ile

6.46b

5.10b

14.05b

0.58a

0.60a

0.59a

0.55b

0.91b

0.72a

0.53b

0.36b

2.88a

Osi

6.53a

5.42a

17.40a

0.60a

0.54b

0.38b

0.64a

0.95a

0.52b

0.55a

0.43a

2.77a

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test

Table 10. Main Effect of Soil Depth on Soil Chemical Properties in the Study Areas

Soil depth

pH water

pH CaCl2

Conductivity (µscm)

Na

K

Ca

Mg

Na

OM

N (%)

SOC (%)

Ex. Acidity

CEC (meq/100)

0-30

6.21b

5.17b

25.08a

0.57a

0.50b

0.43b

0.57b

0.57a

1.15a

0.72a

0.67a

0.37c

2.6a

30-60

6.27b

4.90c

16.83b

0.60a

0.56a

0.47a

0.60a

0.60a

0.98b

0.51c

0.57b

0.33d

2.6a

60-90

6.14a

5.20a

10.39c

0.44a

0.46c

0.42b

0.46d

0.44a

1.03b

0.66b

0.60b

0.42b

2.4a

90-120

6.38a

4.88d

9.56d

0.55a

0.40d

0.34c

0.49c

0.55a

0.62c

0.65b

0.37c

0.51a

2.4a

120-150

6.42a

4.73e

8.81e

0.43a

0.39d

0.43b

0.50c

0.43a

0.61c

0.43d

0.36c

0.42b

2.7a

Table 11. Interaction Effect of Sites and Location on Soil Chemical Properties in the Study Areas

Sites

Location

pH water

pH CaCl2

Conductivity (µscm)

Na

K

Ca

Mg

Na

OM

N (%)

SOC (%)

Ex. Acidity

CEC (meq/100)

soil

Owu Isin

6.37b

4.70e

10.8e

0.34b

0.29d

0.25d

0.51b

0.34b

1.15b

0.48c

0.66b

0.46a

2.05b

Obbo Ile

6.69a

5.53a

14.9c

0.82a

0.82a

0.94a

0.84a

0.82a

1.25a

0.63b

0.73a

0.37cd

3.99b

Osi

6.47b

5.03d

17.7a

0.80a

0.69b

0.62b

0.86a

0.80a

1.19ab

0.61b

0.69ab

0.43ab

3.60a

concretion

Owu Isin

5.68d

4.12f

1.11e

0.41b

0.20e

0.33c

0.29d

0.41b

0.41e

0.62b

0.24e

0.41bc

1.84b

Obbo Ile

6.23c

5.32b

13.2d

0.34b

0.37c

0.24d

0.25e

0.34b

0.56d

0.81a

0.33d

0.36d

1.76ab

Osi

6.59a

5.17c

17.1b

0.40b

0.40c

0.14e

0.41c

0.40b

0.71c

0.43c

0.41c

0.44ab

1.58ab

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test

Table 12. Interaction Effect of Sites and Soil depth on Chemical Properties in the Study Areas

Sites

Soil Depth

pH water

pH CaCl2

Conductivity (µscm)

Na

K

Ca

Mg

Na

OM

N (%)

SOC (%)

Ex. Acidity

CEC (meq/100)

soil

0-30

6.47bc

5.17b

26.50a

0.70ab

0.65b

0.65b

0.77b

0.70ab

1.51a

0.61c

0.88a

0.37e

3.34a

30-60

6.54b

5.11d

15.83d

0.78a

0.73a

0.69a

0.85a

0.78a

1.21b

0.60c

0.70b

0.30f

3.55a

60-90

6.72a

5.27a

12.17e

0.54a-d

0.57c

0.63b

0.65d

0.54a-d

1.51a

0.76b

0.88a

0.46bc

3.05a

90-120

6.43bc

4.96e

9.00g

0.65ab

0.52c

0.46d

0.70c

0.65ab

0.89c

0.45d

0.52c

0.54a

3.07a

120-150

6.39bc

4.93f

8.33g

0.60a-c

0.53c

0.28e

0.72c

0.60a-c

0.88c

0.45d

0.51c

0.43b-d

2.76a

concretion

0-30

5.96d

5.17b

23.67b

0.44b-d

0.35d

0.21f

0.37f

0.44b-d

0.79cd

0.83ab

0.46cd

0.37de

1.94b

30-60

6.00d

4.70h

17.83c

0.42b-d

0.38d

0.25e

0.36e

0.42b-d

075d

0.44d

0.43d

0.36ef

1.97b

60-90

6.10d

5.14c

8.61g

0.34cd

0.35d

0.21f

0.28c

0.34cd

0.55e

0.57c

0.32e

0.39de

1.77b

90-120

6.33c

4.81g

10.11f

0.45b-d

0.28e

0.22f

0.27f

0.45b-d

0.35f

0.86a

0.20f

0.48b

1.90b

120-150

6.44d

4.53i

8.78g

0.26d

0.25e

0.28e

0.29f

0.26d

0.36f

0.41d

0.21f

0.41c-e

1.69b

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test

Table 13. Interaction Effect of Location and depth on Soil Chemical Properties in the Study Areas

Location

Soil depth

pH water

pH CaCl2

Conductivity (µscm)

Na

K

Ca

Mg

OM

N (%)

SOC (%)

Ex. Acidity

CEC (meq/100)

Owu Isin

0-30

6.17de

4.51i

17.75c

0.47a-c

0.35h

0.36e

0.40fg

1.26a

0.64bc

0.73a

0.39de

2.17ab

30-60

6.00ef

4.53i

14.00de

0.47a-c

0.29i

0.35ef

0.40g

1.15ab

0.61bc

0.67ab

0.36ef

2.04b

60-90

6.00ef

4.45j

7.75ij

0.25bc

0.24ij

0.28g

0.44ef

0.81d-f

0.66bc

0.47d-f

0.41c-e

1.82ab

90-120

5.91f

4.34k

8.25hi

0.51a-c

0.20jk

0.21h

0.39g

0.33h

0.56c

0.19h

0.72a

2.23ab

120-150

6.09ef

4.24l

7.0j

0.19c

0.17k

0.24h

0.36g

0.33h

0.26e

0.19h

0.30fg

1.46ab

Obbo Ile

0-30

6.44c

5.70b

23.75b

0.62ab

0.61cd

0.53c

0.56d

1.10bc

0.90a

0.64bc

0.36d-f

2.88ab

30-60

6.49bc

5.23d

13.50ef

0.62ab

0.69ab

0.54c

0.67b

0.71e-g

0.37d

0.42e-f

0.25g

2.97ab

60-90

6.49bc

5.91a

14.92d

0.56a-c

0.63bc

0.67b

0.48e

1.02c

0.68b

0.59c

0.35ef

2.84ab

90-120

6.40c

5.09f

11.17g

0.51a-c

0.46fg

0.51c

0.45e

0.87d

0.99a

0.50d

0.37d-f

2.50ab

120-150

6.47bc

5.17e

6.92j

0.59ab

0.59cd

0.73a

0.59cd

0.83de

0.65bc

0.48de

0.29b

2.99ab

Osi

0-30

6.03ef

5.31c

33.75a

0.63ab

0.55de

0.41d

0.77a

1.08bc

0.61bc

0.63bc

0.36ef

2.92ab

30-60

6.34cd

4.96g

23.00b

0.71a

0.70a

0.54c

0.75a

1.07bc

0.57c

0.62bc

0.38de

3.28a

60-90

6.77a

5.24d

8.50h

0.51a-c

0.50ef

0.31fg

0.48e

1.26a

0.65bc

0.73a

0.52b

2.52ab

90-120

6.83a

5.22d

9.25h

0.62ab

0.56de

0.31fg

0.63c

0.66g

0.40d

0.38g

0.44b-d

2.76ab

120-150

6.69ab

4.78h

12.50f

0.53a-c

0.41g

0.33e-g

0.67d

0.69fg

0.38d

0.40fg

0.48bc

2.62ab

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s test.

Table 14. Interaction Effect of farm Sites, Location and depth on P fraction in the Study Areas

Farm Sites

Locations

Soil depth

H20

NaHCO3 (mg/Kg)

NaOH (mg/Kg)

1M HCL (mg/Kg)

Conc. HCL (mg/Kg)

0.5M H2SO4 (mg/Kg)

NaHCO3 (mg/Kg)

NaOH (mg/Kg)

1M HCL (mg/LKg)

Conc. HCL (mg/Kg)

soil

Owu Isin

0-30

0.26l-n

268.61

322.99h

200.29f-h

1.47n-p

1212.63i-k

176.09

11.56s

164.05h

0.71b

30-60

0.24mn

487.00l

342.30f

127.09o

3.66g-j

977.76r

443.72f

36.96k

89.06p

0.04j-l

60-90

0.28k-m

208.17

192.91p

143.50n

4.97c-f

1572.55b

148.78

313.68b

113.95l

0.46cd

90-120

0.37j

903.91c

210.54mn

226.51d

5.10c-f

1197.61jk

376.85j

39.21g

166.15g

0.49c

120-150

0.37dj

385.95o

185.93q

157.63m

4.62d-g

1735.41a

406.53h

31.23l

61.28t

0.01l

Obbo Ile

0-30

0.24m-o

216.23

388.78b

197.61f-i

2.35l-n

1376.17e

650.68b

13.78qr

216.12c

0.87a

30-60

0.20no

497.90k

216.66l

113.20q

2.01m-p

1333.01f

212.07s

14.77q

147.16i

0.24f-i

60-90

0.35jk

299.06r

178.76r

166.67lm

3.64g-j

1064.11no

298.68p

41.87i

98.20n

0.12i-l

90-120

0.28k-m

276.84t

188.73q

202.20e-g

2.67j-m

1118.38lm

477.83e

17.18p

83.90q

0.04jl

120-150

0.47i

220.75

158.02s

225.47d

1.09p

1065.72no

310.64n

4.58t

222.78b

0.72h

Osi

0-30

1.56a

616.68j

14.64

174.07kl

2.54k-n

1416.18d

305.66o

16.72p

212.17d

0.29e-h

30-60

1.24c

905.35c

15.82

188.08ij

4.49d-h

926.92s

70.66

19.87o

91.65o

0.07j-l

60-90

1.28c

729.06f

368.23d

308.10bc

1.22op

1294.54g

93.00

14.58q

212.84d

0.42c-e

90-120

1.31c

888.72d

251.25j

193.66g-i

2.33l-n

941.61s

64.33

201.09d

105.91m

0.23f-i

120-150

1.27c

963.91b

125.13t

204.68ef

3.16i-l

1133.88l

72.67

202.27d

22.36o

0.30e-g

concretion

Owu Isin

0-30

0.22m-o

693.86h

373.68b

192.69g-i

2.19l-o

1203.10i-k

770.06a

36.45k

45.65

0.16g-k

30-60

0.26l-n

212.61

329.13g

174.46kl

1.63m-p

1245.40h

392.38i

12.61rs

302.79a

0.91a

60-90

0.33j-l

460.10m

202.66o

178.12jk

4.26e-h

1006.89qr

543.13c

26.41n

56.96

0.03j-l

90-120

0.40ij

305.73p

211.68m

29.99r

4.05f-i

1091.84mn

421.96g

25.04n

143.98j

0.32d-f

120-150

0.35jk

643.69j

116.89

212.32e

5.26c-e

1287.18g

338.56l

37.89k

91.37o

0.17g-j

Obbo Ile

0-30

0.16o

107.90

398.55a

133.08no

6.54a

1033.55pq

342.11k

426.21a

77.79s

0.02kl

30-60

0.24mn

60.09

207.76n

314.61bc

6.36ab

1304.40fg

198.94

96.09f

115.88l

0.33d-f

60-90

0.74gh

179.88

231.05k

232.04d

5.09c-f

1061.02op

313.95m

48.18h

143.01j

0.17g-j

90-120

0.67h

276.84t

252.79j

12.59r

4.59d-g

1221.19h-j

498.04d

29.21m

97.16n

0.02jk

120-150

0.75fg

71.67

116.89

127.03o

4.90c-f

947.59s

296.17q

29.99lm

80.73r

0.04j-l

Osi

0-30

0.82f

442.09n

295.05i

306.66c

5.98a-c

1088.31no

152.33

39.77j

190.95f

0.68b

30-60

0.71gh

303.51q

216.46l

129.82o

3.46h-k

1071.60no

113.99

197.09e

222.34b

0.65b

60-90

0.93e

873.72e

13.80

317.68ab

5.48a-d

1229.03hi

218.64r

31.24l

163.30b

0.16g-k

90-120

1.40b

968.00a

251.25j

190.67hi

5.38b-d

1183.95k

44.81

40.35ij

122.10k

0.25f-i

120-150

1.13d

708.43g

25.13

327.99a

4.02f-i

1535.23c

206.82t

291.87c

195.23e

0.15h-l

Means with the same superscript along the same column are not significantly different (p>0.05) based on Turkey’s