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Phosphorus Sorption in Soils Overlying Basement Complex Rock, Alluvium, Coastal Plain Sand and Imo Shale Parent Materials

This study aimed at evaluating phosphorus (P) sorption capacities in Soils overlying basement complex Rock (A), Alluvium (B), coastal plain sand (C) and Imo shale (C) parent materials. Completely randomized design was used to collect soil samples from 5 depths in 3 replications from Idanre, Koko, NIFOR and Uhomora in Nigeria. Samples collected were analyzed in the central analytical laboratory of the Nigerian Institute for Oil palm Research, Benin City, Nigeria between march 2016 and September 2017. 60 soil samples were equilibrated in 25 ml of 0.01 M CaCl2 containing various concentration of P as KH2PO4 to give 0, 50, 100, 150, 200 and 250 mg/L P for 24 hours (h) at room temperature 25 ± 2 o C. Genstat statistical package was used to calculate Analysis of variance, correlation of Original Research Article Orhue et al.; AJSSPN, 7(3): 41-54, 2021; Article no.AJSSPN.68638 42 Phosphorus sorption index (PSI) with soil properties, coefficient of variation, means separation and Least Significant difference (LSD). The rate and %P adsorption increased with increasing concentration of P added to the soils. The P sorption capacities of the soils considering Freundlich model decreased in the order of D > B > C >A. %P adsorbed was highest in D soils with value of 15.19% for 100 mg/kg P added. The PSI correlated with organic carbon r = -0.58 P ≤ .05 in C soils, r = 0.44 P ≤ .05 in D soils, it also correlated with N r = -0.58 P ≤ .05 in C Soils, K r = 0.57 P ≤ .05, r = 0.49 P ≤ .05 in C and D soils respectively. D soils sorbed more P than other soils hence the D soils will require more P fertilization to attain optimum P concentration in soil solution, however further study is required to determine the form of P sorbed by these parent materials.


INTRODUCTION
Phosphorus (P) is an essential macronutrient elements needed for plant growth, as it increases the physiological efficiency of crops. When phosphate fertilizers are applied to soils or dissolved by soil water, a substantial amount of the applied Phosphate are adsorbed on the solid phase reducing the use efficiency of the phosphate fertilizers [1]. P sorption can be said to occur when P added to soils or sediments undergo a fast surface reaction and slow reaction of P on solid phase [2]. Many tropical soils adsorb large amount of applied phosphates applied as fertilizers, P sorption is greatest in soils containing oxides, clay and allophane, followed by kaolinitic and lastly montmorillonitic clays [3,4].
In Acid soils P can largely be fixed by oxides, hydroxides and oxyhydroxides of iron (Fe), Aluminum (Al), Manganese (Mn) and clay minerals which makes it less available or effectively unavailable to plants. The availability of both native and applied P is largely controlled by sorption and desorption which makes phosphorus unavailable to plants. Such is the case of most Nigerian soils as it is dominated by sesquioxides and low activity clay [5,6]. The wide spread occurrence of P deficiency in most arable land in Nigeria has led to intensive use of P fertilizer. Nigerian soils may act as source or sink of P and may exhibit different P sorption capacities. While studies have been conducted on phosphorus sorption status of Nigerian upland soils [7,8,2,4]. None have been reported on the influence of Parent materials on P sorption characteristics thus there is paucity of research information on phosphorus sorption capacities of soils developed on different parent materials. This study was undertaken to provide information on Phosphorus Sorption in Soils Overlying Basement Complex Rock, Alluvium, Coastal Plain Sand and Imo Shale Parent Materials in Ondo, Delta and Edo states, Nigeria.

Description of Study Area
This study was conducted in Idanre, Koko, Nifor and Uhomora in Ondo, Delta and Edo state of Nigeria (Fig. 1)

Soil Sampling
Soil samples were collected randomly from five depths (0-15, 15-30, 30-60, 60-90 and 90-120) cm in three replications from four locations of the study area using the soil Auger. Sixty soil samples collected were stored in labeled polythene bag and taken to the laboratory for further processing and analysis.

Laboratory Analysis
The soils were air-dried at room temperature for 1 week, ground and sieved through a 2mm sieve for analysis. pH was determined in a 1:2 soil to water suspension using a glass electrode pH meter (Tan 1996 [14] respectively. Soil excheangeable bases were extracted by ammonium acetate method buffered at pH 7 [15]. From the extract, Ca and Mg was determined using Bunk scientific USA atomic absorption spectrophotometer (AAS), while K and Na were read with Jenway Germany flame photometer. Effective cation exchange capacity (ECEC) was determined by summation of CEC and EA [16,17].

Phosphorus sorption studies
1g air dried soil was weighed into series of 50 ml plastic bottles and the samples were equilibrated in 25 ml of 0.01 M CaCl 2 containing 0, 50, 100, 150, 200 and 250 mg/L P for 24 h at room temperature as prescribed by Nair et al. [18]. Three drops of CHCl 3 were added to inhibit microbial activities responsible for organic P mineralization during equilibration. The suspension was shaken for 24 h on a B. Bran scientific and instrument company England reciprocating mechanical shaker. After equilibration, the soil suspension was centrifuged at 7000 rpm for 5 minutes and the clear supernatant was decanted and Phosphorus concentration determined colorimetrically [19] at 882 nm after 1h using the 1205 Vis spectrophotometer.. The difference between the quantity of P added and the quantity of P in solution after shaking with soil was calculated as the quantity of P sorbed. The P sorption data were calculated from linear Freundlich and Langmuir sorption isotherm. Freundlich equation is given by X = a + C n . Linearizing the equation it becomes log X = Log a + 1/n log C. Where X is the amount of P sorbed per unit weight of soil (mg P kg -1 soil), C is the concentration of P in the equilibrium solution (mgL -1 ) a is constant related to sorption capacity, it is the Y-intercept of the plot, n is the phosphate sorption energy obtained from dividing the slope of the plot by 1. A plot of log X against log C gives a straight line with slope 1/n. Langmuir equation is given by C/x = 1/Kb + C/b Where, C = Concentration of P in soil solution at equilibrium (mg P L -1 ), x = Amount of P adsorbed (mg kg -1 soil), b = Adsorption maximum (mg P kg -1 soil), 1/K b = Y-Intercept and K = Constant, i.e. adsorption affinity (L mg -1 P) K was obtained by dividing the slope (1/b) by intercept (1/K b). Plots of C/x versus C produce a straight line with a slope 1/b.PSI was determined according to procedure of Bache and Williams [20]. Adopted by Aghimien et al. [2] where the amount of P sorbed (x) mg kg -1 from addition of 1.5 g P kg -1 soil was determined after shaking with B. Bran scientific and instrument company England reciprocating mechanical shaker for 24 h at a water to soil ratio of 10 : 1. The PSI was then calculated using the quotient X /log C. where C is the solution equilibrium P concentration.

Statistical Analysis
Data obtained were subjected to analysis of Variance (ANOVA), correlation of PSI and soil physical and chemical properties, Duncan multiple range test at 5% level of probability and LSD at α = .05 using the VSN international Ltd 12.1 (PC/windows vista) UK Genstat statistical package (8 th Edition). Difference between means ≥ LSD value were reported to be significantly different while difference between means < LSD value were not significantly different

Physical and Chemical Properties
The physical and chemical properties of the soils are shown in (Table 1 and 2). The chemical properties were moderately acidic in the D and A soils, and strongly acidic in B and C soils, which could be due to the nature of the Parent material overlying the soils. The Organic carbon content of the soils varied and decrease significantly down the soils depths amongst the parent materials in the order of A > C > B > D. The high Organic carbon content at the surface soil could be due to high liter fall from vegetations growing on the location. The soils total N and available P were also low. The low total N and available P status of the soils may be attributed to low organic matter contents as organic matter is a major reservoir of soil P and N. Particle size distribution showed that Sand is the dominant soil fraction and tends to decrease with soils depths in all the parent materials except in B soils. The dominant sand fraction could be attributed to the nature of the parent materials as reported by Brady and Weil [21]. The textural classes were sandy clay loam in all the parent materials except in B soils which was loamy sand.

P Adsorption Isotherms
The relationship between amount of P adsorbed versus amount of P in solution at equilibrium are shown in Fig. 2. It was observed that the amount of P adsorbed increased with increased amount of P added. At specific amount of P in concentration the amount of P adsorbed by soil B was higher than other soils parent material, this could be due to high adsorbtion capacity of B soils. A close linear relationship between P adsorbed and P remaining at equilibrium was established and the correlation coefficient obtained from the plot were 0.93, 0.89, 0.94 and 0.93 for A, B, C and D soils respectively. The P adsorbed by the soils is shown in (Tables 3 and  4). The amount of P adsorbed increased with increase in the concentration of P added to the different soils this could be due to difference in the maximum P adsorption capacities of the different parent materials. At 0, 50, 100 mg/L P added, mean amount of P adsorbed varied in all the soils. However it was very close. The mean amount of P sorbed by B soils was highiest when 150 and 200 mg/kg P was added. It had values of 97.20 and 133.20 mg/kg P respectively. In A and B Soils (Table 3), C and D (Table 4), %P adsorbed increased with the increased amount of P added. The %P adsorbed was highest in D soils with values of 9.14% and 15.19% at 50 and 100 mg/kg P added. In A soil %P adsorbed had the highest values of 31.04% at 250 mg/L P added. The difference in the %P adsorbed could be attributed to differences in the capacities of the soils to adsorb P versus nature of parent material. C soil had the least CV value of 1.90% versus amount of P adsorbed. While A, B and D soils were more variable with CV values of 2.30%, 6.90% and 4.90% respectively. The Relationship between PSI versus soils physical ♦ A soil ■ B soil ▲ C soil X D soil and chemical properties have been reported by Aghimien et al. [2]. In this study PSI significantly correlated positively and negatively with some soil chemical properties in C and D soils at P ≤ .05 level of significance (Table 5). In C soils, the PSI was significantly and negatively correlated with organic carbon with r = -0.578 P ≤ .05, total N r = -0.578 P ≤ .05 and K r = 0.566 P ≤ .05. However, in D soils PSI significantly and positively correlated with organic carbon r = 0.438 P ≤ .05, K r = 0.497 P ≤ .05.
Langmuir and Freundlich generated parameter presented in (  [23] found that ability of the Freundlich model to describe P adsorption curves was superior to Langmuir model for calcareous soils. However, Amjad et al. [24] had reported comparable results for prediction of P adsorption by both Langmuir and Freundlich models. The Feundlich equation described P sorption satisfactorily in these soils. The goodness-of fit of Freundlich model to the sorption data may indicate that adsorbed P by the soils and the Concentrations of added P are within the range of validity of the isotherms. This is consistent with findings of Aghimien et al. [2], which found that P sorption data obtained from some hydromorphic soils of southern Nigeria fitted well to freundlich data with r 2 values > 0.95 indicating very high conformity of the adsorption data to the Freundlich model.

CONCLUSION
P sorption characteristics are important in designing best p management practice to reduce the risk loss or under application of p. the results obtained in this study reveal that estimation can be done on PSI as difference in the magnitude of change in PSI between the soils indicate that soil parent material in addition to the amount of P added to the soil will determine a soil potential to release P. the study reveal that D soils sorbed more P than soils of other parent materials studied indicating that soil d will need more p fertilization to attain optimum P concentration in soil solution. The results of the study showed that P adsorbtion increased with increased amount of P added indicating that the amount of P adsorbed versus P concentration at equilibrium gives an indication of the adsorption process in different soils. the result also showed that both langmuir and freundlich adsorption models are robust in predicting p adsorption however in comparing both models it may be concluded that the freundlich model is better fitted over the langmuir model considering the r