Phosphorus Sorption Research Articles

Phosphorus Sorption and Saturation in the Ganges Tidal Floodplain Soils of Bangladesh

The soils developed from the Ganges sediments in the coastal area of Bangladesh and India extend several thousand hectares and important from the view point of rice cultivation. Phosphorus, one of the important environmental and agricultural element, retention behavior of the Ganges floodplain soils is poorly reported. The objective of this study was to determine maximum phosphorus adsorption capacity (MPAC) and to develop Psat for 13 Ganges Tidal Floodplain soils of Bangladesh. The MPAC value and Psat based on Mehlich-3 extractions were determined. The conventional adsorption equations, such as the Langmuir, Freudlich and Temkin equations were used to describe the P sorption of the studied soils. The MPAC value varied from 1250 to 2000 mg/kg and correlated with EC (r = 0.59, p<0.05) and CEC (r = -0.74, P<0.01). The sorption capacity of the tested soils ranged from 511 to 545 mg/kg and the calculated energy of adsorption of the soils varied from 0.192 to 1.00 μg/mL and it was a positively correlated with clay (r=0.7, p<0.01) and CEC (r = 0.63, p<0.05) but negatively with silt (r= -0.80, p<0.01), pH (H2O) (r=-0.60, p<0.05) and with MPAC (r=-0.59, p<0.05) values. Phosphorus saturation indices of the studied sample demonstrated a far below the threshold critical limit of 25%.

Mechanism analysis of soil amelioration and phosphorus recovery by using a mineral soil conditioner in southern China

This study aims to identify the processes and mechanisms affecting physicochemical properties of soil following application of mineral soil conditioner and to investigate the behavior of PO4 sorption among 1:1 and 2:1 clay minerals and Fe/Al oxides in a ferralsol. Three replicates of five treatments, i.e., (1) a control without any application of inorganic P (CK), (2) inorganic P fertilization (CKP), and (3) combinations of inorganic P fertilization with mineral soil conditioner applied at 750 (M1), 975 (M2), and 1200 (M3) kg ha−1, were used to explore the influence of phosphate (PO4) sorption capacity and dynamic changes in clay mineralogy in the ferralsol, as examined using geochemical modeling (Factsage 6.1) and physical measurements (zeta potential, XPS, FTIR, and XRD analysis). We have found that the new formation of illite (a 2:1 phyllosilicate) was generated from the kaolinite (a 1:1 phyllosilicate) in the ferralsol after mineral soil conditioner (MSC) application. The iron in the ferralsol as well as the K+, Mg2+, and Si4+ in the MSC, played important roles in the clay mineral transformation. Meanwhile, the observed trends of phosphorus sorption competition suggested that the PO4 sorption capacity of the 2:1 clay minerals may be close to or even higher than that of the 1:1 clay minerals and Al oxides. The effects of Fe oxides on PO4 sorption could be ignored when Al oxides were present in the ferralsol. In comparison to the control and P-fertilized treatments, the PO4-binding capacity of the clay minerals in the MSC treatments could exceed that of the Al oxides because of the new formation of 2:1 clay minerals (illite). We demonstrate that the combination of zeta potential, XRD, FTIR, and XPS analysis is a promising strategy for distinguishing relationships between clay minerals and Al oxides in terms of phosphorus sorption. The MSC application was highly effective for soil amelioration and phosphorus sorption.

Phosphorus-mineralizing Communities Reflect Nutrient-Rich Characteristics in Japanese Arable Andisols.

Elucidating the soil phosphorus cycle driven by soil microbes is a vital question in soil microbial ecology. The Japanese arable Andisols, occupying half of the Japanese cropland, are known for their high phosphorus sorption capacity. However, limited information is currently available on microbially driven phosphorus mineralization in arable Andisols. We herein report that the phosphorus-mineralizing community in the Japanese arable Andisols showed characteristic distribution and composition patterns, from those in other types of soils. We performed a chemical analysis and microbial community analysis of 43 arable Andisols along the Japanese archipelago. Soil phosphomonoesterase activities measured at pH 11 were approximately 70% of those at pH 6.5, which indicates that alkaline phosphatase contributes to phosphorus cycling, although most soil samples were acidic. Functional gene predictions based on 16S rRNA gene sequencing indicated that the alkaline phosphatase gene phoD was more abundant than other alkaline phosphatase genes and, thus, plays major roles. Hence, amplicon sequencing targeting phoD was performed and the results obtained showed that alphaproteobacterial phoD was dominant. This is in contrast to previously reported phoD compositions in other soils and may be attributed to the nutrient conditions in arable Andisols, which favor copiotrophic Alphaproteobacteria. Furthermore, the composition of phoD correlated with soil pH and bioavailable phosphorus concentrations rather than carbon or nitrogen concentrations. These results were partly different from previous findings, varying in the soil types and geographic ranges of sampling sites. Collectively, the present results indicate that the phosphorus-mineralizing community in the Japanese arable Andisols is regulated differently from those in other soil types.

Kinetics and Thermodynamics of Phosphorus Sorption on Goethites: Effects of Biochar Application

Bioavailability of phosphorus (P) in soils is controlled by, inter alia, the presence of iron (Fe) and aluminum (Al) oxides, which readily bind with P. Biochar has been suggested for minimizing P sorption to oxides and, therefore, improving P availability to plants. However, the kinetics and temperature dependence of biochar influence on P sorption are poorly understood. The objective of this study was, therefore, to determine the kinetics and thermodynamics of P sorption by goethite as affected by biochar application at 0 and 40 g kg−1 oxide. Batch equilibration tests were run at 15, 25, and 35 °C, and solution P concentrations were measured 0.5, 1, 3, 6, 9, 12, and 24 h after the start of incubation. Sorption of P by the oxides followed pseudo-first-order kinetics. Biochar application enhanced cumulative P sorption by both oxides, and the increase was greater for Al-goethite. Phosphorus sorption increased as temperature increased from 15 to 25 °C but declined at 35 °C. Phosphorus sorption on biochar-amended oxides was associated with low activation energy (Ea) values, indicating that the sorbed P in soils containing goethite and Al-goethite could still be plant available. This information will contribute towards a better understanding of processes affecting biochar effects on P fate in soils.

Nano-rod Ca-decorated sludge derived carbon for removal of phosphorus.

Recovering phosphorus (P) from waste streams takes the unique advantage in simultaneously addressing the crisis of eutrophication and the shortage of P resource. A novel calcium decorated sludge carbon (Ca-SC) was developed from dyeing industry wastewater treatment sludge by decorating calcium (Ca) to effectively adsorb phosphorus from solution. The X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques were used to characterize the Ca-SCs, followed by isotherm and kinetic sorption experiments. A preferred design with CaCO3 to sludge mass ratio of 1:2 was found to have a sorption capacity of 116.82mg/g for phosphorus. This work reveals the crucial role of well-dispersed nano-rod calcium on the Ca-SC surface for the sorption of phosphorus. Moreover, the decoration of nano-rod calcium was found to further promote the uptake of phosphorus through the formation of hydroxylapatite (Ca5(PO4)3(OH)). Thus, the development of decorated Ca-SC for sorption of phosphorus is very important in solving the P pollution and resource loss.

Assessment of phosphorus availability in soil cultivated with ruzigrass

Growing ruzigrass (Urochloa ruziziensis) in crop rotation systems has been suggested as a strategy to increase soil phosphorus (P) cycling and P availability. However, despite increased P lability shown in routine soil analysis, decreased grain yields of crops grown after ruzigrass have been observed. The objective of this study was to evaluate soil P availability to maize (Zea mays) in low or high-P soil cropped to ruzigrass. Soil P lability was evaluated using Hedley fractionation and pearl resin extractions, and P desorption/adsorption was assessed by isothermal titration calorimetry (ITC). Phosphorus changes in soil-P fractions in the maize rhizosphere were studied in a greenhouse experiment. Growing ruzigrass resulted in higher resin-extractable P and soil organic matter (SOM) contents than fallow. However, in soil cropped with ruzigrass, maize P uptake and P desorption were lower, and P adsorption to soil was higher than soil under fallow. In general, organic P bound to Fe and Al was non-available. Phosphorus sorption as assessed with ITC was a better indicator of P bioavailability to maize than pearl resin and Hedley fractionation, and suggested that P was less bioavailable after ruzigrass due to increased SOM, which resulted in the formation of metal phytate and more effective organo-metal sites for ligand exchange. Greater P solubility and availability in fallowed soil appeared to be partly due to the dissolution of Ca-related P, greater P desorption, and less potential for P adsorption. Isothermal titration calorimetry is a useful semi-quantitative tool for understanding P sorption behavior.

Adsorption and risk of phosphorus loss in soils in Amazonia

Low availability of phosphorus in Amazonian soils is the result of both naturally occurring low levels and adsorption processes in the soil. These factors encourage the use of intensive phosphate fertilizations to increase productivity, which, in turn, increases P saturation and contamination risk. This study was designed to determine the adsorption capacity, as well as the risk of P loss and contamination of water bodies by P in Amazonian soils. Eleven soils located in zones free from any alteration were selected in order to set parameters for natural conditions for the local soils. Adsorption experiments were carried out in CaCl2 solution 0.01 mol L−1, containing 0 to 200 mg L−1 of P in the form of KH2PO4. The phosphorus sorption index (PSI) was determined, and soluble and available forms of P were extracted in water, Mehlich-1, Olsen, and CaCl2 solutions. The phosphorus saturation degree (PSD) was obtained by extraction with acid solution of ammonium oxalate. PSI was lower in the soil GL (Eutric Gleysol) and higher for NT (Rhodic Nitisol), while the maximum adsorption capacity (Smax) was lower in the soil AR (Ferralic Arenosol) and higher in AC1 (Haplic Acrisol 1). The PSD was higher in AT (Hortic Anthrosol) which also showed higher values of soluble and available P, while lower saturation values were observed in FR2 (Xanthic Ferralsol), FR4 (Rhodic Ferralsol), Haplic Acrisol 2, and Eutric Gleysol (< 5%). These soils presented low to medium maximum adsorption capacity and low P saturation; however, Ferralic Arenosol soil showed a high risk of P loss, making P management very difficult. Similarly, Hortic Anthrosol showed high susceptibility to P loss.

Phosphorus sorption to suspended sediment in freshwater

The effect of flow transport on phosphorus sorption to suspended sediment was investigated by combining field experiments with indoor experiments. The phosphorus distribution was found to be spatially variable and the phosphorus concentration gradient between pore water and overlying water decreased with sediment resuspension in the Huaihe River. Indoor experiments were conducted in a batch reactor and an elongated flume. Flow transport accelerated phosphorus sorption onto suspended sediment and the time to reach quasi-equilibrium decreased with an increase in flow velocity in dynamic water. Both phosphorus sorption amount and sorption rate were affected by the flow velocity, the initial phosphate concentration and suspended sediment concentration. The influence of flow velocity on phosphorus sorption amount was found to be controlled by the variance of the initial phosphate concentration. When compared with other isothermal adsorption models, the Langmuir equation provided the best description of the phosphorus sorption performance of the hydrodynamic experiments. Adsorption and desorption were not exactly equal, and the phosphorus sorption amount fluctuated with time in a quasi-equilibrium state in the flume experiments.

Phosphorus sorption with modified sediments from a malodoroussr iver:r: kinetics, equilibrium, and thermodynamic studies

Phosphorus sorption with modified sediments from a malodoroussr iver:r: kinetics, equilibrium, and thermodynamic studies

Bioretention Media for Enhanced Permeability and Phosphorus Sorption from Synthetic Urban Stormwater

AbstractA high-flow medium (HFM), modified with two aluminum-based amendments, alum and partially hydrolyzed aluminum (PHA), is used to achieve enhanced dissolved P removal and promote high infiltr...

Characterization of phosphorus interaction with sediments affected by acid mine drainage - relation with the sediment composition

Phosphorus sorption capacity was investigated in surface sediments derived from an abandoned zinc-lead mine area located in northeastern Algeria. The forms and the distribution of phosphorus in the raw sediment were identified using the sequential chemical extractions method. Batch experiments were done to study the adsorption kinetics and isotherms. The pH effect was evaluated by macroscopic and infrared analyses. In raw sediment, speciation results show that phosphorus is dominantly bound to oxyhydroxides. Sorption experiments demonstrate that phosphorus uptake is principally related to sediment composition. The nature of the dominant iron oxyhydroxide has a substantial role in the adsorption capacity and the mechanism interaction. The adsorption kinetics can be described by the second order and Elovich models. The isotherms data are successfully modeled by the Temkin equation. The maximum phosphorus removal is reached under acidic pH. Spectroscopic analyses reveal that the predominance of jarosite implies electrostatic interaction with sediment particles. However, in the case of schwertmannite predominance, phosphate ions are adsorbed by the ligand exchange mechanism.

Soil phosphorus sorption capacity after three decades of intensive fertilization in Mato Grosso, Brazil

Abstract Soil phosphorus (P) availability commonly limits the productivity of tropical croplands. While large fertilizer inputs can alleviate P limitation, this strategy is costly and relies on finite phosphate rock resources subject to price volatility. Nevertheless, high-P-input agriculture on P-poor and P-fixing soils is spreading rapidly in some regions of the tropics, particularly in Brazil, where farmers on average add twice as much P to soils as they harvest to ensure high yields. Here we ask whether P fertilizer inputs to tropical soils in excess of harvested P outputs will eventually build up a residual pool of soil P that crops can tap into if fertilizer inputs are decreased – a phenomenon observed in the U.S. and Western Europe, albeit on very different soils. We pose this question in Mato Grosso, Brazil, where we quantified soil P input-output budgets, total P, Bray-extractable P, P sorption capacity, P saturation, and other characteristics from a chronosequence of 31 plots that had been in soybean production for 0–31 years. Farmer interviews revealed ongoing annual additions of P fertilizer greater than P removals in crops, with an average farm P balance in the most recent year, including soybeans and a second harvest, of +14 kg P ha −1 y −1 . Soil total P and Bray-P 1 have increased, and P sorption capacity has decreased, with time in production. However, clayey soils rich in iron- and aluminum-oxides still have high P sorption capacity and low P saturation, even after three decades of intensive fertilization and residual P build-up. Our findings suggest that commodity crop producers farming on this soil type in Mato Grosso and other tropical regions may need to add annual inorganic P fertilizer inputs greater than the quantity of P recovered in harvests for up to a century or more before soil P budgets can be balanced without endangering yields. This result has implications for the sustainability of agricultural intensification in the tropics.

Phosphorus sorption-desorption and effects of temperature, pH and salinity on phosphorus sorption in marsh soils from coastal wetlands with different flooding conditions

Wetland soils act as a sink or source of phosphorus (P) to the overlaying water due to phosphorus sorption-desorption processes. Litter information is available on sorption and desorption behaviors of phosphorus in coastal wetlands with different flooding conditions. Laboratory experiments were conducted to investigate phosphorus sorption-desorption processes, fractions of adsorbed phosphorus, and the effects of salinity, pH and temperature on phosphorus sorption on soils in tidal-flooding wetlands (TW), freshwater-flooding wetlands (FW) and seasonal-flooding wetlands (SW) in the Yellow River Delta. Our results showed that the freshly adsorbed phosphorus dominantly exists in Occluded-P and Fe/AlP and their percentages increased with increasing phosphorus adsorbed. Phosphorus sorption isotherms could be better described by the modified Langmuir model than by the modified Freundlich model. A binomial equation could be properly used to describe the effects of salinity, pH, and temperature on phosphorus sorption. Phosphorus sorption generally increased with increasing salinity, pH, and temperature at lower ranges, while decreased in excess of some threshold values. The maximum phosphorus sorption capacity (Qmax) was larger for FW soils (256 mg/kg) compared with TW (218 mg/kg) and SW soils (235 mg/kg) (p < 0.05). The percentage of phosphorus desorption (Pdes) in the FW soils (7.5–63.5%) was much lower than those in TW (27.7–124.9%) and SW soils (19.2–108.5%). The initial soil organic matter, pH and the exchangeable Al, Fe and Cd contents were important factors influencing P sorption and desorption. The findings of this study indicate that freshwater restoration can contribute to controlling the eutrophication status of water bodies through increasing P sorption.

Phosphorus accumulation and sorption characteristics of P-enriched soils in the Dian Lake basin, southwestern China

The eutrophication of the Dian Lake is very serious. Phosphorus (P)-enriched soils in the southern basin can contribute significantly to the overall P loads in the Dian Lake. The objective of the present study was to investigate the distribution of P fractions and the P sorption properties in the P-enriched soils along the Chai river, southern of the Dian Lake. The information is essential to understanding P discharge from the intensively cropped field to waterways. Soil samples were collected in five sites located along the Cha river at the southern part of the basin of the Dian Lake, southwestern China, from the upstream cropped fields to the estuary buffer, respectively. Soil total phosphorus (TP), inorganic P fractions, organic carbon (SOC), N, pH, and particle size distribution were quantified. Phosphorus sorption was modeled with the simple Langmuir equations. Total P, loosely bound, and non-occluded inorganic P (Pi) concentrations at all soil depths (0–80 cm) were significantly higher in the upstream Ferrisols than that in the downstream Gleysols of the Chai river. However, the occluded Pi concentrations were significantly higher in the Gleysols than that in the Ferrisols. Phosphorus in the 0–80 cm soil profile of both Ferrisol and Gleysols are largely dominated by Ca-bound Pi (47–79%). The higher sorption maximum (Smax), binding energy (k), and equilibrium buffering capacity (PEBC) and lower zero equilibrium P concentration (EPC0) over all sampling depths were observed in the Gleysols than that in the Ferrisols. The increase of Smax, k, and PEBC and decrease of EPC0 as sampling depth increased suggest that there might be fewer P losses via leaching process both in the upstream and downstream areas of the Chai river. It is evident from this study that the upstream areas is actually acting as a source for dissolved P, whereas the downstream areas is acting as a sink. Moreover, management options to reduce P losses in land runoff may therefore be a more effective way to minimizing eutrophication risk in the P-enriched area.

Phosphorus Sorption Behavior of Torrefied Agricultural Byproducts under Sonicated Versus Non-Sonicated Conditions

The application of agrichar derived from organic feedstocks has the potential to improve soil fertility and crop production by providing major nutrients like phosphorus (P) to the crop, and in some cases also reducing P leaching. The effect of agrichar on the leaching of P in soils is not uniform and can vary depending on the type of agrichar and amount applied. The objective of this study was to (i) evaluate the behavior of four agrichars (rice hulls RH, palm fronds PF, horse bedding HB, and bagasse BG) for their ability to retain/release P and (ii) determine the effect of wet sonication on P sorption behavior. The feedstocks were torrefied at 500 °C using a top-lit updraft gasifier and used in multiple batch incubation experiments to evaluate equilibrium phosphorus concentration, maximum P sorption capacity (Smax), and adsorption/desorption potential. Both, RH (12.6 g kg-1) and HB (11.5 g kg-1) contained 10-15 times higher total P concentration than PF and BG, rendering RH and HB as potentially suitable products to be used as soil amendments. However, this initial P content of the agrichar seemed to have an overriding effect on the P sorption behavior of the agrichar. PF had Smax of 676 (±127) mg kg-1 for the non-sonicated agrichar, and 237 (±91) mg kg-1 following sonication. There was significant increase in CEC for PF and BG agrichar upon sonication. PF agrichar increased from 27 (±3) cmolc kg-1 to 41 (±4) cmolc kg-1 with sonication. Similarly, BG agrichar CEC increased from 21 (±2) cmolc kg-1 to 45 (±5) cmolc kg-1 with sonication. Initial total P and Ca concentration and their ratios was found to play significant roles on P adsorption and desorption. Major cations like Ca, Fe, Al and Mn are found to act as active sorption site for phosphorus controlling its fate and mobility along with compounding effects of other physicochemical parameters.

Polydentate Ligand-Like Substances in Manure Impacting Soil Sorption and Transport of Phytate Phosphorus

The mechanisms by which complex products released from the organic matrix of cattle manure impact phosphorus (P) behavior and transport are largely undefined. Effects of a dairy slurry isolate on sorption characteristics of three benchmark soils and the breakthrough of phytate-P were determined in short soil columns of Mattapex loam (fine-silty, mixed, active, mesic Aquic Hapludults) under saturated flow conditions. The manure liquid isolate was obtained after a 7-day incubation of reconstituted dairy manure (1.6:1, feces-to-urine) at 37 °C and centrifugation at 16,000×g. The liquid isolate, at dilutions of 20:1 to 4:1 water-to-isolate, decreased soil sorption of phytate-P, with reduction in loge K averaging 30%. Whether the influent contained artificial rainwater or the manure isolate at a water-to-isolate ratio of 20:1, P retention and breakthrough curves were differentially impacted. Only inorganic phosphate-P was eluted in a multiple-stage process, and breakthrough occurred after 16 pore volumes of rainwater. Both inorganic- and enzyme-labile P (TBIOP) appeared in the effluent when either a dilute solution of 0.05 M EDTA (ethylenediamine-N, N, N′, N′-tetraacetate) or one containing 5% of manure liquid isolate was used as influent. The polydentate ligand-like substances reduced (i) the soil’s affinity for phytate and (ii) the hydrolysis rate in soil, allowing phytate to be eluted. Therefore, dissolved components of the manure matrix played critical roles in controlling transport and dispersion of phytate-derived P forms in soil and may hold the key to the understanding of biogeochemical bases of persistent effects of legacy P in agricultural watersheds.

Distribution of phosphorus-solubilizing bacteria in relation to fractionation and sorption behaviors of phosphorus in sediment of the Three Gorges Reservoir.

Phosphorus (P) fractionation and sorption behavior as well as the abundance and community composition of phosphorus-solubilizing bacteria (PSB) in sediments, including inorganic phosphate-solubilizing bacteria (IPB) and organic phosphate-mineralizing bacteria (OPB), were investigated in 27 sampling sites of five sections in the Three Gorges Reservoir (TGR) in December 2012. The calcium-bound phosphorus (CaCO3∼P) accounted for the largest part for P fractions in the sediment of TGR, which was paralleled with IPB outnumbering OPB. Furthermore, some PSB isolates, such as Micromonospora sp., Aminobacter sp., and Arthrobacter sp., were shared by the IPB and OPB. Thus, some IPB species functioned as OPB and vise versa, which could be further reflected by a negative and significant relationship between PSB (IPB+OPB) number and content of CaCO3∼P together with acid-soluble organic phosphorus (ASOP). Spatially, the highest ASOP content in the section Mudong and the highest CaCO3∼P plus iron-bound phosphorus (Fe(OOH)∼P) as well as equilibrium phosphorus concentration (EPC0) in the sections of Yunyang and Zigui due to sediment sequestration by the dam, as well as the positive relationship between EPC0 and the ratios of different phosphorus species and phosphorus sorption maximum (Q max), jointly indicated pathway diversification and potential risk of phosphorus release mediated by PSB in TGR.

Inhibition of phosphorus sorption on calcite by dairy manure-sourced DOC

In confined animal feeding operations, such as dairies, manure is amended to soils at high rates leading to increases in P and organic matter in the soils. Phosphorus reacts with soil-Ca to form Ca-P minerals, which controls P availability for leaching and transport through the watershed. In this research, the effects of manure sourced dissolved organic matter (DOM) on P sorption on calcite were measured at different reaction times and concentrations. Reactions were monitored in 1% and 10% manure-to-water extract solutions spiked with P. When manure-DOM was present, a significant reduction in P sorption occurred (2–90% absolute decrease) compared to samples without manure-DOM. The greatest decrease occurred in the samples reacted in the 10% manure solution. XANES spectroscopic analysis showed that at 1% manure solution, a Ca-P phase similar to hydroxyapatite formed. In the calcite samples reacted in the 10% manure solution, K-edge XANES spectroscopy revealed that P occurred as a Ca-Mg-P phase instead of the less soluble hydroxyapatite-like phase. Results from this study suggest that in manure-amended calcareous soils, increased DOM from manure will decrease P sorption capacity and increase the overall P concentration in solution, which will increase the mobility of P and subsequently pose greater risks for impairment of surface water quality.

Influence of Granularity of Sediment from a Water Reservoir on Phosphorus Sorption Processes

This research was designed to investigate the mechanism of phosphorus adsorption behaviour on the fine- ( 0.063 mm) sediments of the Klusov water reservoir (Slovakia) due to the different particle cohesiveness. The study of the sediment physical parameters indicated that the clay/silt fraction dominates in fine-grained sediment sample and the silt/sand fraction in coarse-grained one. Based on the study of physico-chemical properties of sediments, it can be concluded that sediment particle size, specific surface area, organic content and aluminium content are the main sorption influencing factors. The Langmuir-Freundlich isotherm model was used to describe the phosphorus adsorption process of two different grain-size fractions of reservoir sediments. The R2 values of fitting (0.99 for fine- and 0.98 for coarse-grained sediments) revealed very well the description of the P sorption process by the Langmuir-Freundlich isotherm model. The results demonstrated a maximum phosphorus sorption capacity of 325 mg P/kg for fine-grained sediment and 207 mg P/kg for coarse-grained sediment. Reservoir sediments indicated maximum P sorption efficiency at low P content in solution and the release of phosphorus from sediment into water was observed without the addition of adsorbate. The results of this study indicate that the fine- and coarse-grained sediments of the Klusov water reservoir act as an efficient trap for phosphorus.

Phosphorus Sorption in Hydromorphic Soils Overlying Alluvium and Coastal Plain Sand Parent Materials in Delta State, Nigeria

ABSTRACTHighly weathered soils of the tropics are known to have great affinity for phosphate sorption with reportedly high values for affinity constant, k. This study evaluated soil samples from profiles dug at Agbor, Kwale, and Otegbo which overly alluvium and coastal plain sand parent materials for their capacities to sorb phosphorus (P). The samples were equilibrated in 30 ml of 0.01 M calcium chloride (CaCl2) containing various amounts of P as monopotassium phosphate (KH2PO4) to give 0, 25, 50, 100, 150, 200, 400, 800, and 1000 μg/L P for 6 days at a temperature of 25 ± 2°C. The rate of P adsorption increased with increased concentrations of P and was generally low in the soils. Affinity constant k was also low and did not compare with values earlier obtained for well-drained soils. P adsorption capacity decreased in the order: Agbor > Otegbo > Kwale. Percent phosphorus sorbed was highest at Agbor with values of 11.33%, 10.8%, and 10.12% for 50, 100, and 150 mg/kg P added, respectively. The adsorption maxima (b) of the soils was significantly correlated with the soils organic carbon with r = 0.817, p < 0.05; r = 0.883, p < 0.05, and r = 0.886, p < 0.05 for Agbor, Kwale, and Otegbo soils, respectively. Proper management of the soils organic matter content coupled with the addition of rock phosphate is recommended for P improvement in these soils for sustained cultivation of crops such as Raphia hookeri that are adapted to hydromorphic environment.