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Biochar (BC) is a soil fertility enhancer, regarded as a potential carbon sequester and nutrient leaching preventer. Various studies have shown better phosphorus (P) availability with adding biochar. However, limited reporting is available on absorption–desorption behaviour of added P and dose optimisation of biochar. Rice straw biochar (RSB) and acacia biochar (ACB), prepared by slow pyrolysis at optimised temperature and pyrolysis time, were incubated at different rates (0, 5, and 10 g kg−1) in loamy sand and clay loam soils to study P sorption compared to the unamended control. The data was observed to be best fitted into Langmuir adsorption isotherm for P adsorption. The effects on maximum P adsorption, bonding energy, and adsorption rate constants were lower in loamy sand compared to clay loam soil. The values of maximum P desorption (Dm) and desorption rate constant (Kd) decreased with the application of biochar. A linear regression equation optimised the amount of P addition for soil amendments. For the soil with inherent P content, rice biochar was the best option (5 g kg−1), while for soils lacking in P, ACB is optimised at 5 g kg−1 with external P input of 1 mg P kg−1 of test soil. This data can be recommended to the farmers as a best practice for the P addition, along with managing farm wastes as biochars to enhance nutrient availability.

Abstract Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g−1 from the solution at pH 7 and 192.8 mg g−1 from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L−1 NaNO3) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO4 and Mg(H2PO4)2 (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater. Graphical Abstract

The information on changes in phosphorus (P) sorption and desorption characteristics and transformations after biochar application to high P fixing soils is still unclear. In the present study, we evaluated the differential response of biochar derives from five different farm waste viz. Lucaena sp., Albbizia sp., Mangifera indica, Triticum aestivum and Oryza sativa applied at 1 and 3 g kg−1 (w/w) on P sorption and desorption in three texturally different (silt loam, clay loam and sandy loam) soils. The amount of P sorbed by the clay loam was significantly (p

Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g−1 from the solution at pH 7 and 192.8 mg g−1 from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L−1 NaNO3) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO4 and Mg(H2PO4)2 (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater. Highlights: Bio-assembled MgO-coated biochar composite (MTC) was prepared and used for P sorption MTC removed 58.8 mg P g−1 from P solution and 192.8 mg P g−1 from fermentation liquid Precipitation and ligand exchange governed P sorption in solution Struvite formation and ligand exchange controlled P sorption in fermentation liquid MTC can be effectively used for P removal from the fermentation liquids [ABSTRACT FROM AUTHOR]

This paper presents the results of a research on the impact of the composition of bottom sediments on their phosphate sorption capacity under aerobic and anoxic conditions. The research was carried out in 2013–2016 with the use of bottom sediments from two small-scale retention reservoirs (the Ożanna reservoir and the Rzeszów reservoir). A physical and chemical analysis of the bottom sediments was carried out, which led to the conclusion that the sediments deposited at the bottom of the examined water bodies differ both in terms of their physical properties and chemical composition. The isotherm best describing the course of phosphate sorption in the deposits of the examined reservoirs, as well as the theoretical maximum phosphate sorption capacity of the sediments (qmax) under close-to-real conditions (i.e., on undisturbed sediment cores), were determined. The analysis of the results allowed to conclude that the phosphate sorption capacity of the sediments is influenced both by the aerobic conditions and the physical and chemical properties of the sediments, such as the granulometric composition, pH, organic matter content and the content of metals with which phosphorus forms sparingly soluble compounds. [ABSTRACT FROM AUTHOR]

Permafrost thaw releases nutrients and metals from previously frozen soils and these nutrients may affect important biogeochemical processes including methane (CH4) production and oxidation. Here we assessed how concentrations of nutrients, solutes, and metals varied across four plant communities undergoing permafrost thaw and if these geochemical characteristics affected rates of CH4 production and oxidation. We tested nutrient limitation in CH4 production and oxidation by experimentally adding nitrogen (N), phosphorus (P) and a permafrost leachate to peat across these four plant communities. The upper 20 cm of permafrost contained 715 ± 298 mg m−2 of extractable inorganic N and 20 ± 6 mg m−2 of resin-extractable phosphorus (Presin), for a N:P ratio of 36:1. These low amounts of Presin coincide with high acid-digestible aluminum (Al), iron (Fe), and P concentrations in the permafrost soil and suggest that P may accumulate via sorption and constrain easily available forms of P for plants and microbes. Permafrost leachate additions decreased potential CH4 production rates up to 80% and decreased CH4 oxidation rates by 66%, likely due to inhibitory effects of N in the permafrost. In contrast, organic and inorganic P additions increased CH4 oxidation rates up to 36% in the tall graminoid fen, a community where phosphate availability was low and CH4 production was high. Our results suggest that (1) inorganic N is available immediately from permafrost thaw, while (2) P availability is controlled by sorption properties, and (3) plant community, nutrient stoichiometry, and metal availability modulate how permafrost thaw affects CH4 production and oxidation. [ABSTRACT FROM AUTHOR]

The paper presents new reactive materials, namely marl and travertine, and their thermal modifications and the Polonite® material, analyzing their phosphorus removal from water and wastewater by sorption. Based on the experimental data, an analysis of the factors influencing the sorption capacity of the materials, such as the material dose, pH of the initial solution, process temperature, surface structure, and morphology, was performed. Adsorption isotherms and maximum sorption capacities were determined with the use of the Langmuir, Freundlich, Langmuir–Freundlich, Tóth, Radke–Praunitz, and Marczewski–Jaroniec models. The kinetics of the phosphorus sorption process of the tested materials were described using reversible and irreversible pseudo-first order, pseudo-second order, and mixed models. The natural materials were the most sensitive to changes in the process conditions, such as temperature and pH. The thermal treatment process stabilizes the marl and travertine towards materials with a more homogeneous surface in terms of energy and structure. The fitted models of the adsorption isotherms and kinetic models allowed for an indication of a possible phosphorus-binding mechanism, as well as the maximum amount of this element that can be retained on the materials' surface under given conditions—raw marl (43.89 mg P/g), raw travertine (140.48 mg P/g), heated marl (80.44 mg P/g), heated travertine (282.34 mg P/g), and Polonite® (54.33 mg P/g). [ABSTRACT FROM AUTHOR]

Biochar (BC) is a soil fertility enhancer, regarded as a potential carbon sequester and nutrient leaching preventer. Various studies have shown better phosphorus (P) availability with adding biochar. However, limited reporting is available on absorption–desorption behaviour of added P and dose optimisation of biochar. Rice straw biochar (RSB) and acacia biochar (ACB), prepared by slow pyrolysis at optimised temperature and pyrolysis time, were incubated at different rates (0, 5, and 10 g kg−1) in loamy sand and clay loam soils to study P sorption compared to the unamended control. The data was observed to be best fitted into Langmuir adsorption isotherm for P adsorption. The effects on maximum P adsorption, bonding energy, and adsorption rate constants were lower in loamy sand compared to clay loam soil. The values of maximum P desorption (Dm) and desorption rate constant (Kd) decreased with the application of biochar. A linear regression equation optimised the amount of P addition for soil amendments. For the soil with inherent P content, rice biochar was the best option (5 g kg−1), while for soils lacking in P, ACB is optimised at 5 g kg−1 with external P input of 1 mg P kg−1 of test soil. This data can be recommended to the farmers as a best practice for the P addition, along with managing farm wastes as biochars to enhance nutrient availability. [ABSTRACT FROM AUTHOR]

The development of techniques for the rapid, inexpensive, and accurate determination of the phosphorus (P) availability and sorption index (PSI) in soils is important for P management in highly weathered tropical soils. The applicability of near- and mid-infrared reflectance spectroscopy (NIR and MIR) as tools for estimating P availability and PSI was assessed over a wide range of highly weathered soils in Madagascar. The predictions were based on chemometric methods using multivariate calibration models with partial least squares (PLS) regressions, and pedotransfer functions (PTFs). Chemometric methods failed to predict available P (Presin). However, a P sorption index, determined as the P remaining in solution (Prem), was estimated with acceptable accuracy with both NIR and MIR (R2cv = 0.70 − 0.73; R2v = 0.65 − 0.77; SEP(c) = 5.5 − 4.6 mg kg−1). The PTFs showed that the PSI was well explained by iron oxide, gibbsite, and sand contents, all of these compounds being well predicted by NIR or MIR (R2v > 0.70). These results indicate that NIR and MIR can be helpful for a rapid estimate of PSI of highly weathered ferralitic soils. [ABSTRACT FROM AUTHOR]

Due to non-renewable resources and the need to meet the world’s food needs, phosphorus is considered a strategic resource. As a component of agricultural fertilizers, phosphorus is the main factor causing the eutrophication process, which makes it necessary to the efficient removal of phosphorus from wastewater, will also enable the recovery of this element remove it in wastewater treatment plants. Currently used wastewater treatment methods, based on biological phosphorus binding or its chemical precipitation, force high investment and operating costs, with simultaneous insufficient phosphorus removal. Modern technologies designed to purify wastewater from phosphorus compounds are based on reactive materials that bind phosphorus in adsorption and precipitation processes, while allowing its recovery in subsequent stages. The paper presents an analysis of two natural marl and travertine materials, their thermal modifications and filter material Polonite® in terms of phosphorus binding by sorption and precipitation under static conditions. The research took into account the influence of the elemental composition of the materials, the initial concentration of P, fraction size, process conditions and the temperature of thermal treatment of natural materials in terms of phosphorus retention. Marl showed a higher phosphorus binding efficiency with increasing the initial concentration, reaching a maximum of 91.93% phosphorus reduction. At a concentration of 188.72 mg P/L, the marl showed the highest sorption capacity at the level of 8.72 mg P/g. Travertine achieved the highest phosphorus binding efficiency of 89.82% at an initial concentration of 20.26 mg P/L, while the highest sorption capacity of travertine equal to 7.10 mg P/g was demonstrated at the initial concentration of 188.72 mg P/L. Commercial material Polonite® achieved the highest phosphorus binding efficiency (95.09%) at the initial concentration of 20.26 mg P/L. In terms of the process parameters under static conditions, the most optimal for marl, travertine and Polonite® are 350 rpm shaking speed and 24 h shaking time. Research using materials with different fraction sizes have shown that the most appropriate particle size is 1–2 mm due to the best phosphorus removal efficiency. Thermal treatment of both marl (at temperatures between 600°C–1,000°C) and travertine (at temperatures between 650°C–1,000°C) clearly increases their phosphorus binding efficiency up to 99% reduction. The high efficiency of thermally modified materials was maintained regardless of the process conditions and the size of the fraction. [ABSTRACT FROM AUTHOR]

Increasing areas of agricultural land in high rainfall areas of Sub-Saharan Africa (SSA), where crop production used to be reliable, are affected by soil acidity. This review focuses on the extent, causes and effect of soil acidity on soil properties and crop yield and its management from the context of SSA. Studies showed that the detrimental effects of soil acidity can be mitigated through liming, integrated acid soil management and the use of acid-tolerant germplasms. Application of lime resulted in yield increments of 34–252% in wheat, barley and tef, 29–53% in faba bean and soybean, and 42–332% in potato in Ethiopia, 111–182% in maize in Kenya, and 45–103% in Mucuna in Nigeria under moderate to severe acid soil conditions. This was accompanied by a corresponding increase in soil pH up to 1.9 units and a decrease in exchangeable acidity and aluminum up to 2.1 cmol kg−1. Use of acid-tolerant crop varieties such as maize expressing superior tolerance to Al toxicity resulted in a yield increase of 51% under low soil pH in Cameroon and Kenya. Overall, soil acidity covering ∼35% of SSA should be reclaimed with lime and integrated acid soil management interventions, which could significantly increase crop yield and enhance the resilience of the tropical agroecosystems. .

Increasing areas of agricultural land in high rainfall areas of Sub-Saharan Africa (SSA), where crop production used to be reliable, are affected by soil acidity. This review focuses on the extent, causes and effect of soil acidity on soil properties and crop yield and its management from the context of SSA. Studies showed that the detrimental effects of soil acidity can be mitigated through liming, integrated acid soil management and the use of acid-tolerant germplasms. Application of lime resulted in yield increments of 34–252% in wheat, barley and tef, 29–53% in faba bean and soybean, and 42–332% in potato in Ethiopia, 111–182% in maize in Kenya, and 45–103% in Mucuna in Nigeria under moderate to severe acid soil conditions. This was accompanied by a corresponding increase in soil pH up to 1.9 units and a decrease in exchangeable acidity and aluminum up to 2.1 cmol kg−1. Use of acid-tolerant crop varieties such as maize expressing superior tolerance to Al toxicity resulted in a yield increase of 51% under low soil pH in Cameroon and Kenya. Overall, soil acidity covering ∼35% of SSA should be reclaimed with lime and integrated acid soil management interventions, which could significantly increase crop yield and enhance the resilience of the tropical agroecosystems.. [ABSTRACT FROM AUTHOR]

The paper presents new reactive materials, namely marl and travertine, and their thermal modifications and the Polonite® material, analyzing their phosphorus removal from water and wastewater by sorption. Based on the experimental data, an analysis of the factors influencing the sorption capacity of the materials, such as the material dose, pH of the initial solution, process temperature, surface structure, and morphology, was performed. Adsorption isotherms and maximum sorption capacities were determined with the use of the Langmuir, Freundlich, Langmuir–Freundlich, Tóth, Radke–Praunitz, and Marczewski–Jaroniec models. The kinetics of the phosphorus sorption process of the tested materials were described using reversible and irreversible pseudo-first order, pseudo-second order, and mixed models. The natural materials were the most sensitive to changes in the process conditions, such as temperature and pH. The thermal treatment process stabilizes the marl and travertine towards materials with a more homogeneous surface in terms of energy and structure. The fitted models of the adsorption isotherms and kinetic models allowed for an indication of a possible phosphorus-binding mechanism, as well as the maximum amount of this element that can be retained on the materials’ surface under given conditions—raw marl (43.89 mg P/g), raw travertine (140.48 mg P/g), heated marl (80.44 mg P/g), heated travertine (282.34 mg P/g), and Polonite® (54.33 mg P/g).

The development of techniques for the rapid, inexpensive, and accurate determination of the phosphorus (P) availability and sorption index (PSI) in soils is important for P management in highly weathered tropical soils. The applicability of near- and mid-infrared reflectance spectroscopy (NIR and MIR) as tools for estimating P availability and PSI was assessed over a wide range of highly weathered soils in Madagascar. The predictions were based on chemometric methods using multivariate calibration models with partial least squares (PLS) regressions, and pedotransfer functions (PTFs). Chemometric methods failed to predict available P (Presin). However, a P sorption index, determined as the P remaining in solution (Prem), was estimated with acceptable accuracy with both NIR and MIR (R2cv = 0.70 − 0.73; R2v = 0.65 − 0.77; SEP(c) = 5.5 − 4.6 mg kg−1). The PTFs showed that the PSI was well explained by iron oxide, gibbsite, and sand contents, all of these compounds being well predicted by NIR or MIR (R2v > 0.70). These results indicate that NIR and MIR can be helpful for a rapid estimate of PSI of highly weathered ferralitic soils.

Purpose: Nitrogen (N) and phosphorus (P) are the key elements leading to eutrophication, and it is important to jointly control N and P release from sediments into the water column. Methods: Different mixed materials including P sorbent, natural organic carbon (C), and an oxidizing agent were applied in a 1-year pilot-scale experiment. Results: The addition of iron-rich (IR) clay and Phoslock agent promoted the formation of iron bound P (Fe(OOH)~P) and calcium bound P (CaCO3~P) in sediments, respectively. IR clay offered more advantages in immobilization of phosphorus as refractory P, and the Phoslock agent more effectively reduced the risk of P release into water, which was expressed as a low equilibrium P concentration (EPC0). Mixtures of sugarcane (SU) detritus and IR clay exhibited high carbohydrate (CHO) contents, which further fuelled both denitrification and dissimilatory nitrate reduction to ammonium (DNRA). This indicated that the SU dosage should be controlled to avoid DNRA over denitrification. Attention should be given to the fact that SU introduction significantly promoted the generation of an anaerobic state, leading to the desorption and release of Fe(OOH)~P, which could be alleviated by using Oxone. Multienzyme activity analysis showed that P and N transformation shifted from P desorption to organic P hydrolysis and from ammonification to denitrification and DNRA, respectively. Conclusion: We recommend the use of P sorbent and organic C combined with oxidizing agents as effective mixed materials for sediment remediation, which could enhance P adsorption and provide electron donors for denitrification, while also avoiding the generation of anoxia. [ABSTRACT FROM AUTHOR]

The associations of elements upon a heterogeneous surface may control nutrients or pollutants sorption and release, having agricultural and environmental implications. This chemical behavior can be elucidated by spatial spectroscopy, followed by image analysis. The purpose of this paper is to present a working procedure for image analysis using the free program ImageJ that can be applied for dot maps of three or more elements produced by solid-state spectroscopy. Detailed step-by-step instructions lead to visual and quantitative information regarding elements associations. The working procedure was demonstrated for P, Al and Ca dot maps produced by scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) for surfaces of Al-based water treatment residuals (Al-WTRs), a by-product of drinking water pretreatment with alum coagulant. Al-WTR was reused to adsorb the macro-nutrient P from polluted soil leach and dairy wastewater (WW). Surficial P onto Al-WTR, SL-Al/O-WTR, and WW-Al/O-WTR (0.56, 0.93, and 2.15%, respectively) displayed sorption dynamics, mostly with Al and Ca. Quantification of the spatial proportions of individual elements and their associations indicated P-Al pool > P-Ca pool (45–24% and 17–7%, respectively). Upon introducing P-rich dairy wastewater, the behavior of P sorption by Al and Ca changed and became more clustered. A ternary phase of P-Al-Ca covered 38% of the area with signal, compared to 4.3 and 4.6% of the area in Al-WTR and SL-Al-WTR, where it was limited to particles edges only. Thus, the presented protocol may promote employing image analysis for geochemical applications, elucidating chemical behavior and affinities. Advantages and pitfalls are discussed.

Iron-rich phosphorus (P) sorption materials (PSMs) are often used in P removal structures, a best management practice able to sequester dissolved P from surface runoff, subsurface drainage, and wastewater. The use of bottom-upward flow in these structures is of great interest, but it creates an intrinsic complication: the presence of stagnant water between flow events may cause structures to develop anoxic conditions. It is unknown whether the redox sensitivity of iron (Fe), the predominant element in Fe-rich PSMs, will affect P binding under anoxic conditions. Understanding the potential impact of intermittent anoxic conditions on the solubility of previously adsorbed P is imperative for determining the feasibility of the bottom-up flow design. The objective of this research was to investigate the (1) development of anoxic conditions in the presence of Fe-rich PSM and tile drainage, (2) Fe-bound P mobilization and solubility, and (3) changes in P sorption capacity of Fe-rich PSMs after oxic conditions are restored. Three Fe-rich PSMs were tested in batch incubation studies: acid mine drainage residual, Fe-coated alumina, and steel metal shavings. Non-treated and P-treated PSM samples were incubated in biogeochemical reactors for as long as necessary to reach Eh = −200 mV. After incubation, dissolved P concentrations in P-treated samples and non-treated samples were similarly low, indicating stability of P retention of PSMs under anoxic conditions. The P removal ability of non-treated PSMs before and after undergoing incubation was not significantly altered, as determined in flow-through experiments. Potentially harmful trace metals were not detected in the incubated solutions. Our research shows that the development of anoxic conditions does not significantly impact PSMs Fe-bound P dissolution, and the P removal ability of PSMs persists after oxic conditions are reestablished. [Display omitted] • Incubated Fe-rich PSMs underwent anoxic conditions in the presence of tile drainage. • The effect of the reductive dissolution of Fe on P release and sorption was minor. • Among P-treated PSMs, only one sample released dissolved P beyond detection limits. • P sorption capacity of PSMs was not significantly different pre- and post-incubation. • Iron-rich PSMs can be used in bottom-up flow P removal structures. [ABSTRACT FROM AUTHOR]

Colloid-facilitated phosphorus (P) migration plays an important role in P loss from farmland to adjacent water bodies. However, the dynamics of colloidal P (P coll) release as influenced by irrigation in alkaline calcareous soil remains a knowledge gap. The present study, monitored the dynamic change of P coll under different water management strategies: 1) control, 2) flooding, and 3) alternating flooding and drying cycles. Soil water-dispersible colloids (0.6 nm-1 μm) were extracted by combining filtration and ultrafiltration methods. The contents of P, cation and organic carbon in the water-dispersible colloids were determined and the stability and mineral composition of colloidal fractions were characterized. The results showed that P coll ranged from 16.5 to 25.5 mg kg−1 and represented 42.8%–64.9% of the water-extracted P in the control. Flooding significantly decreased the P coll content by 16.0%–62.1% (mean 32.7%) and it may be attributed to the dissolution of colloidal iron (Fe) bound P. The alternating flooding and drying treatment significantly reduced the P coll content by 11.6%–88.0% (mean 67.6%). The P coll content of the flooding event was always greater than the P coll content of the drying event during flooding and drying cycles. Redundancy analysis and random forest modeling showed that the colloidal calcium (Ca) and ionic strength in soil solutions had negative correlations with the P coll content, and pH, ionic strength and truly dissolved P were the critical factors affecting P coll. Drying of the flooded soil led to the decrease of pH and the increase of ionic strength, colloidal Ca content and positive charges of colloid surfaces, which promoted colloid aggregation and enhanced soil P sorption capacity. This restricted the loss potential of P coll. In summary, controlled flooding and drainage when managed correctly have a role to play in mitigating P coll loss from P-enriched calcareous soils. [Display omitted] • Colloidal P accounts for 53.2% of water-extracted P in the calcareous soil. • Alternating flooding and drying cycles decrease the colloidal P by 67.6%. • Enhanced colloidal aggregation explains the decrease of colloidal P content. • The positive charges on colloid surface increased when soil moisture dropped. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is naturally present in soils. However, urbanization can promote additional inputs of P into the soil that lead to saturation of the binding sites exceeding the maximum sorption capacity. Soils saturated with P act as important diffuse sources of pollution of water resources. The flow of P from the soil to aquatic ecosystems is an aggravating factor for water scarcity, especially in the semiarid region. Knowing phosphorus dynamics in the soil is essential to protect water quality and ensure its multiple uses. In this paper, a total of fifty soil samples, twenty-five from natural soils and twenty-five from urban soils, were evaluated for the effect of urbanization on P sorption characteristics and their relationship with the physical and chemical attributes of the soil. The soil samples were characterized physically and chemically, and the P sorption characteristics were obtained from the adjustment of Langmuir and Freundlich equations by nonlinear regression. Urbanization results in increased soil P saturation and reduced P sorption capacity. Our results show that the sandy texture of the soils studied had a standardizing effect on the soil's physical properties, maintaining, even after urbanization, the physical quality similar to natural soil. In contrast, pH (in water and KCl), base saturation, sodium saturation, potential acidity, exchangeable Al3+, exchangeable Mg2+, available P, and P-rem are valuable indicators in the segregation between natural and urban soils. The reduction of P sorption capacity in urban soils increases the risks related to P loads in aquatic ecosystems that experience urban expansion worldwide. These data serve as a basis for decision-making regarding the appropriate soil monitoring and management of urban expansion areas in watersheds to control P flow to aquatic systems. [Display omitted] • Knowledge about P saturation index of soil leads to better water quality management. • Urban sandy soils have a lower P sorption capacity and a higher P saturation index. • After urbanization, risks of P pollution in water bodies should not be neglected. • P saturation index is associated with higher pH and base saturation. [ABSTRACT FROM AUTHOR]

The static fertilisation experiment conducted in Skierniewice (Central Poland) since 1923 investigates the effect of mineral fertilisation with lime (CaNPK) or without lime (NPK) on the accumulation and release of phosphorus in reference to phosphorus sorption properties in the sandy soil profile. In the case of application of same doses of mineral fertilisers, the content of total phosphorus was higher in NPK than CaNPK soil. Parameters related to sorption capacity and bonding energy from Langmuir and Freundlich model of P sorption were significantly lower in CaNPK than NPK soil profile. This was particularly caused by a lower content of poorly crystallised hydro(oxide) aluminium and iron forms in CaNPK than NPK soil. Higher content of oxide-extractable and bioavailable phosphorus extracted with double lactate solution, dissolved reactive phosphorus in water solution as well as degree of phosphorus saturation in the CaNPK soil profile suggests higher mobility and possibility of occurrence of losses of phosphorus from the profile of limed soil than from acidified soil. Therefore, management of phosphate fertilizers on permanently limed sandy soils requires the optimisation of phosphorus doses to a greater degree corresponding to the actual take-off of the element with crop. An additional finding of the study was evidence of the possibility of re-estimating contents of bioavailable phosphorus and, as a consequence, the degree of phosphorus saturation with Mehlich3 method in strongly acid soil receiving P mineral fertilisers, which can make it difficult to use the test for fertiliser recommendation.

Phosphorus leaching from soils is a major environmental concern leading to eutrophication of water bodies. Three different soil types namely black, red and alluvial soils from Nagpur, Raipur and Kanpur were taken for the study. Soil column leaching experiment was conducted during 2014–15 with different levels of P (0, 50, 100, 150, 300, 600 mg L−1) application with the objective to evaluate P buildup and vertical distribution in different soil types. Soluble reactive P (RP) content in three soils increased slowly with P application rates and decreased with increase in number of leaching events. Total P in leachate followed the similar trend. Phosphorus leaching mainly occurred during the initial seven leaching events accounting to 50–60% of total P leached over whole period. Among the various soil types RP content in leachate followed the order alluvial (0.01–0.23 mg l−1) followed by red (0.01–0.17 mg l−1), and black (0–0.1 mg l−1) soil. Soluble reactive P (RP) accounting for 75–80% leaching mainly during initial 10 leaching events with alluvial soil leached highest P followed by red and black soils. Vertical distribution and movement of Olsen and bray P content in all the soils were higher beneath 0–10 cm depth and increased with P application and decreased in untreated column section. Environmental test like water extractable P (WEP) and CaCl 2 P content were higher in alluvial soil, suggesting the greater potential of P leaching loss under chemical P fertilization. The result of the study can further be extended at field level for efficient P management in various soil types and thus could quantify the contribution of P from different sources to P leaching in agricultural land. [ABSTRACT FROM AUTHOR]

Purpose: The construction of riparian buffer strips has become increasingly important due to the effective phosphorus (P) retention of the strips, thus preventing eutrophication in freshwater ecosystems. The key mechanism is P sorption in soils. To provide some suggestions for increasing the sorption ability of P, the relationships between P sorption behavior and both land use patterns and distance from the shoreline were determined. Materials and methods: In April, July, and October 2013, field investigations were carried out along the shoreline of Lake Chaohu. Eleven sections, including 36 sampling sites at different distances from the shoreline, were chosen, and these sections contained different types of riparian buffer strips, such as grassland, farmland, forest, wetland, and forest/grassland. The P species, sorption parameters, and dominant vegetation species were analyzed. Results and discussion: The total P (TP) and P sorption maximum (Qmax) showed no recognizable seasonal variation and were closely correlated with the distance from the shoreline. The further the distance from the shoreline, the higher the TP and Qmax values, suggesting that soil traits could determine the P sorption extent. However, the Olsen-P content and equilibrium P concentration (EPC0) fluctuated greatly, with the peak occurring in spring and the minimum occurring in summer in the majority of the sampling sites. In addition, positive relationships existed between the TP content and the Qmax value as well as the Olsen-P content and the EPC0 value. Canonical correlation analysis (CCA) further showed that the Olsen-P content and EPC0 values were closely related to the dominant vegetation species, indicating that land use patterns played a decisive role in regulating the P sorption strength and the level of available P. Conclusions: To effectively adsorb P (increase Qmax) and prevent P leaching (reduce the EPC0), we recommend changing the land use patterns (more constructed wetlands and forests with grass) in riparian buffers. [ABSTRACT FROM AUTHOR]

Abstract Phosphorus (P) is usually enriched in urban soils but the environmental consequences of this P enrichment are not well understood. The objective of this study was to investigate P sorption characteristics as a measure of potential P loss from urban soils due to P enrichment via runoff and leaching. We collected soil samples at 0–5 and 5–15 cm soil depths from urban park areas in Nanchang, China, a rapidly expanding city with low P contents in its natural soils. Soil P sorption indices were characterized by a multiple-point isotherm batch experiment. The 0–5 cm layer had lower Langmuir P sorption maximum (S max) than the 5–15 cm layer, probably because of its lower amorphous Al oxide (Al ox) content and higher soil organic carbon (SOC) content. Stepwise multiple regression showed that the combination of Al ox and SOC were the two most important soil properties related to S max of the studied soils. A two-piece segmented linear regression was fitted to the relationships between labile P fractions (i.e., water extractable-P and anion exchange resin-extractable P) and binding energies (k) and the change point values were identified for k below which labile P decreased linearly. Soils below the change point had greater contents of SOC and exchangeable Ca and Mg and higher pH than those above the change point. These results suggest that parent materials played a major role in regulating P sorption capacities of the urban soils, particularly for the soils in urban green spaces. However, the enrichment of Ca and Mg derived from dissolution of calcareous materials in urban areas could significantly influence P bonding strength and saturation ratio of urban soils. Highlights • Urban soil showed stratification in P sorption between 0–5 and 5–15 cm soil layers. • Original soil and parent materials controlled P sorption capacity of urban soil. • Enriched Ca/Mg in urban soils increased P mobility. [ABSTRACT FROM AUTHOR]

Abstract Excess phosphorus (P) loading due to anthropogenic activities has been identified as a primary cause of surface water eutrophication, but it is controversial whether P is a contributor to groundwater contamination. In this study, subsurface transport of P to groundwater and its environmental risk across different land uses was investigated in a karstic springs basin, Florida, USA. Eleven sites including 5 agricultural sites, 5 urban, and 1 pine plantation were selected. Boreholes were drilled to collect soils from surface, vadose zone, and aquifer at 0.6 m depth intervals. Water-extractable P (WSP), Mehlich 3-P, Al, and Fe, soil P storage capacity (SPSC), and P sorption isotherm parameters were obtained for soils from selected depths. We found that agricultural sites particularly horse farms, and urban sites with golf courses and septic tanks showed high risk of P leaching with TP concentrations in the groundwater above the numeric criteria for streams in the north central Florida (0.3 mg L−1). Besides land use which reflected P loadings in the surface soils, significant positive correlations of P sorption maximum (S max) with M3-Fe, Al, and organic matter, and the precipitation of P by calcium bicarbonate, imply the mechanism regulating soil P attenuation in vadose and saturated zones, respectively. Negative SPSC values were significantly negatively correlated with WSP in all the zones, suggesting the applicability of SPSC in deep soils. Moreover, high TP concentration was observed in the groundwater at one site where the SPSC value changed from positive in the surface soils to negative in the subsoils, indicating that an additive SPSC value to water table would be more robust for evaluating the potential of P leaching before moving down to the limestone area. Highlights • The SPSC concept is valid for subsoils but additive SPSC values would be more robust. • P loading alone cannot decide the risk of P leaching to groundwater. • P was bound to Fe/Al-oxide, and organic matter in the vadoze zone and precipitated with Ca in aquifer. • Horse farms and urban sites with golf courses have high risk of P leaching to groundwater. [ABSTRACT FROM AUTHOR]

Arctic streams are likely to receive increased inputs of dissolved nutrients and organic matter from thawing permafrost as climate warms. Documenting how Arctic streams process inorganic nutrients is necessary to understand mechanisms that regulate watershed fluxes of permafrost-derived materials to downstream ecosystems. We report on summer nitrogen (N) and phosphorus (P) uptake in streams draining upland soils from the Pleistocene, and lowland floodplain soils from the Holocene, in Siberia's Kolyma River watershed. Uptake of N and P differed between upland and floodplain streams, suggesting topographic variation in nutrient limitation. In floodplain streams, P uptake rate and uptake velocity were higher than N, while upland streams had similar values for all N and P uptake metrics. Phosphorus uptake velocity and size of the transient hydrologic storage zone were negatively related across all study streams, indicating strong influence of hydrologic processes on nutrient fluxes. Physical sorption of P was higher in floodplain stream sediments relative to upland stream sediments, suggesting more physically driven uptake in floodplain streams and higher biological activity in upland streams. Overall, these results demonstrate that high-latitude headwater streams actively retain N and P during summer base flows; however, floodplain and upland streams varied substantially in N and P uptake and may respond differently to inorganic nutrient and organic matter inputs. Our results highlight the need for a comprehensive assessment of N and P uptake and retention in Arctic streams in order to fully understand the impact of permafrost-derived materials on ecosystem processes, and their fate in continental drainage networks.

The information on changes in phosphorus (P) sorption and desorption characteristics and transformations after biochar application to high P fixing soils is still unclear. In the present study, we evaluated the differential response of biochar derives from five different farm waste viz. Lucaena sp., Albbizia sp., Mangifera indica , Triticum aestivum and Oryza sativa applied at 1 and 3 g kg -1 ( w/w ) on P sorption and desorption in three texturally different (silt loam, clay loam and sandy loam) soils. The amount of P sorbed by the clay loam was significantly ( p <0.05) higher than the silt loam and sandy loam, regardless of added P concentration. The Freundlich isotherms exhibit a better fit (R 2  = 0.564-0.996 in silt loam, 0.640-0.993 in clay loam and 0.724-0.993 in sandy loam soil) to P sorption data as compared with the Langmuir isotherm. Biochar application significantly decreased the P desorption maxima and desorption constant. The R 2 values ranged from 0.447 to 0.999 in silt loam, 0.438 to 0.996 in clay loam, 0.545 to 0.989 in sandy loam. Lucaena biochar showed highest adsorption maxima, thereby suggesting highest P release, whereas soils treated with Triticum aestivum biochar had the lowest adsorption maxima in both clay loam and sandy loam soil. These results indicated that biochar application can significantly enhance P availability; the extent of which is determined by soil texture and type of biochar. The results of present study highlight that biochar application would help increase soil P availability by enhancing fertilizer-P use efficiency associated with decreased P sorption capacity due to increased flush of available-P in soil colloidal complex., Competing Interests: The authors declare no competing interests., (© 2023 The Authors.)

An important pathway for biochar to alter the availability of soil phosphorus (P) is to change P sorption characteristics of the soil. The aim of this study was to understand the mechanisms of biochar effects on P sorption in acid upland red soils in the presence of different concentrations of exogenous P. Rice straw biochar (RSB) was prepared and applied at rates of 0, 1%, 3%, and 5% ( w/w ) to three red soils (MZ 1 , MZ 2 , and QY 1 ) differing in initial pH (pH = 4.31, 4.82, and 5.68, respectively). The P sorption characteristics of these red soils were described using the Langmuir and Temkin equations and their relationships with soil basic physicochemical properties were analyzed. Furthermore, a representative red soil (MZ 2 ) was selected to analyze the zeta potential of soil colloids and the chemical properties of sorption equilibrium solution, in order to understand their relationships with P sorption characteristics. Results showed that within a certain range of P concentration in the equilibrium solution, the amount of P sorbed by the three red soils decreased and the corresponding amount of P desorbed increased with increasing amendment rate of RSB. RSB showed the greatest effect on P desorption characteristics of MZ 2 soil in the presence of higher exogenous P concentration. With increasing RSB amendment rate, the maximum P sorption of MZ 1 soil decreased, while those of MZ 2 and QY 1 soils increased after an initial decrease. Phosphate sorption equilibrium constant and maximum P buffer capacity of each soil first increased and then decreased. However, a single physicochemical property could not interpret complex changes in multi-factors that jointly determine the P sorption characteristics of red soils. In the case of MZ 2 soil, RSB amendment shifted the zeta potential of soil colloids to the negative direction; this decreased the positive charge and increased the negative charge on the soil surface, thus reducing P sorption in the MZ 2 soil. In the presence of the same concentration of exogenous P, RSB amendment altered the pH, dissolved organic C (DOC), humification index (HIX), and maximum fluorescence intensity (F max ) in the sorption equilibrium solution. In most cases, the amount of P sorbed by the MZ 2 soil was negatively correlated with the pH value, DOC concentration, HIX value, and F max value of humic-like dissolved organic matter (DOM), and positively correlated with the F max value of protein-like DOM ( P  < 0.05 or P  < 0.01). The relative fractional distribution of the contents for humic-like and protein-like DOM might determine the difference in the P sorption characteristics of MZ 2 soil. In conclusion, different amendment rates of RSB affected the release of phosphate from soil surfaces into the solution by altering basic physicochemical and electrochemical properties of red soils and chemical properties of sorption equilibrium solution. [ABSTRACT FROM AUTHOR]

Biochar is recognized as an effective material for recovering excess nutrients, including phosphorus (P), from aqueous solutions. Practically, that benefits the environment through reducing P losses from biochar-amended soils; however, how salinity influences P sorption by biochar is poorly understood and there has been no direct comparison on P sorption capacity between biochars derived from different feedstock types under non-saline and saline conditions. In this study, biochars derived from wheat straw, hardwood, and willow wood were used to compare P sorption at three levels of electrical conductivity (EC) (0, 4, and 8 dS m−1) to represent a wide range of salinity conditions. Phosphorus sorption by wheat straw and hardwood biochars increased as aqueous solution P concentration increased, with willow wood biochar exhibiting an opposite trend for P sorption. However, the pattern for P sorption became the same as the other biochars after the willow wood biochar was de-ashed with 1 M HCl and 0.05 M HF. Willow wood biochar had the highest P sorption (1.93 mg g−1) followed by hardwood (1.20 mg g−1) and wheat straw biochars (1.06 mg g−1) in a 25 mg L−1 P solution. Although the pH in the equilibrium solution was higher with willow wood biochar (~ 9.5) than with the other two biochars (~ 6.5), solution pH had no or minor effects on P sorption by willow wood biochar. The high sorption rate of P by willow wood biochar could be attributed to the higher concentrations of salt and other elements (i.e., Ca and Mg) in the biochar in comparison to that in wheat straw and hardwood biochars; the EC values were 2.27, 0.53, and 0.27 dS m−1 for willow wood, wheat straw, and hardwood biochars, respectively. A portion of P desorbed from the willow wood biochar; and that desorption increased with the decreasing P concentration in the aqueous solution. Salinity in the aqueous solution influenced P sorption by hardwood and willow wood but not by wheat straw biochar. We conclude that the P sorption capacity of the studied biochars is dependent on the concentration of the soluble element in the biochar, which is dependent on the biochar type, as well as the salinity level in the aqueous solution. [ABSTRACT FROM AUTHOR]

Purpose: 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.Materials and methods: 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).Results and discussion: 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.Conclusions: 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. [ABSTRACT FROM AUTHOR]

Application of recycling organic wastes is a possible way forward in overcoming increasing costs for mineral fertilizers. However, the result of its side effect can be the unbalanced plant nutrition. This study was carried out to investigate the side effects of phosphorus (P) applied by organic fertilization on biomass yield, agronomic efficiency and P utilization, P balance and soil P transformation in a long-term 27-year (1993–2019) field experiment with maize monoculture. Six treatments including unfertilized control (C), urea ammonium nitrate (UAN), urea ammonium nitrate + wheat straw (UAN+St), sewage sludge (SS), farmyard manure (FYM), and cattle slurry (CS) were applied based on the unified dose of 120 kg N ha−1 year−1 (except C). Following groups of parameters were investigated during the experiment: i) yield characteristics, ii) content of different soil P fractions and iii) soil P sorption characteristics. UAN+St and FYM treatments showed higher average biomass yield as compared to the positive control (UAN) treatment. Positive phosphorus balance was found only in FYM and SS treatments, where the high amount of P applied by SS represents a higher risk of P over-accumulation. On the other hand, the degree of phosphorus saturation of FYM was 8% higher (in 2019) than for SS. Lower mobility of SS phosphorus was confirmed even with lower readily available soil P contents as compared to FYM and CS. The C, UAN, UAN+St, and CS showed a negative P balance during the experiment. However, CS significantly increased the degree of P saturation. The ratio of P-balance from pseudototal P content in soil exceeded + 10% at SS treatment and was lower than − 10% at UAN and UAN+St treatments, respectively. Unfertilized control resulted in the value of 9.23%. FYM represents higher risk of P losses as compared to SS at same dose of applied nitrogen. Long-term application of FYM, SS and CS strongly increased the soil available P pool and degree of phosphorus saturation. When the ratio of P-balance from pseudototal P content in soil exceeds + or − 10% (UAN, UAN+St, and SS), the depletion of P AR reserves (UAN, UAN+St) or P over-accumulation (SS) are starting to be statistically significant and changes of agricultural practices according to P fertilizing have to be considered. • Lower P mobility at sewage sludge treatment is caused mainly due to Fe and Al applied for the P-floculation process. • Farmyard manure represents higher risk of P losses as compared to sewage sludge at same dose of applied nitrogen. • Long-term application of farmyard manure, sewage sludge and cattle slurry strongly increased the soil available P pool. • Sewage sludge, urea ammonium nitrate and urea ammonium nitrate with straw cannot be considered as sustainable system. • Urea ammonium nitrate and urea ammonium nitrate with straw are less sustainable treatments as compared to unfertilized control. [ABSTRACT FROM AUTHOR]

Manure application changes the phosphorus (P) sorption behavior of soil, which may help release P to surface water. Excess P may result in degradation of quality of receiving water. In this study, effects of dairy, poultry, and goat manure applications on various soil phosphorus sorption indices were estimated for a silt loam Bangladeshi agricultural soil. The soil was incubated with manures for a month, and sorption experiments were conducted using incubated soil. The soil P adsorption isotherms conformed to S-curve shape for the both manure treated and untreated soils. Adsorption data conformed to the isotherms in the order of Freundlich > Temkin > Langmuir for poultry and goat manure treated soils and Langmuir > Freundlich > Temkin for dairy manure treated soil. Manure treatment decreased all the sorption parameters; the highest decrease was observed from dairy manure treated soil. Maximum P buffering capacity and standard phosphate requirement were decreased for all manure treatments, meaning that less fertilizer would be needed to maintain P concentrations in soil solution if manure amendment is used. Results of this study could be utilized for better fertilizer and manure management to reduce the waste of valuable fertilizer and to decrease water pollution.

Artificial mixing and phosphorus inactivation methods using aluminum compounds are among the most popular lake restoration methods. Długie Lake (Olsztyńskie Lakeland, Poland) was restored using these two methods. Primarily, P precipitation and inactivation methods significantly increased the sorption properties of Długie Lake bottom sediment. Fifteen years after the termination of the restoration procedure, the alum-modified “active” sediment layer still has higher P adsorption abilities, which can limit P internal loading. Relatively low amounts of phosphates in the near-bottom water of Długie Lake, even in anoxia, as well as the fact that the assessed maximum sediment P sorption capacity is still higher than NH4Cl−P (labile P) and BD−P (Fe-bound P) sum (“native exchangeable P”), confirm that hypothesis. Among the tested P adsorption models for the sediment, the double Langmuir model showed the best fit to the experimental data (the highest R2 values). This may indicate that phosphorus adsorption by the tested sediments most likely occurs through phosphate binding at two types of active sorption sites. P adsorption by the studied lake sediment during experiments was significantly connected to aluminum content in sediment. The research into the adsorption properties of sediment can be used as a tool for the evaluation of lake restoration effects.

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 (CaCO∼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 CaCO∼P together with acid-soluble organic phosphorus (ASOP). Spatially, the highest ASOP content in the section Mudong and the highest CaCO∼P plus iron-bound phosphorus (Fe(OOH)∼P) as well as equilibrium phosphorus concentration (EPC) in the sections of Yunyang and Zigui due to sediment sequestration by the dam, as well as the positive relationship between EPC and the ratios of different phosphorus species and phosphorus sorption maximum ( Q ), jointly indicated pathway diversification and potential risk of phosphorus release mediated by PSB in TGR. [ABSTRACT FROM AUTHOR]

The phosphorus (P) sorption capacity was determined for concrete waste, alum residuals from water treatment sludge, and natural sorbents (shells, clay, kaolin, and mordenite) from various parts of Thailand. The material showing the best P sorption capacity (shells) was selected for preparing a ceramic material to support the growth of nitrifying bacteria. The ceramic material, consisting of shells (50% by weight), alum residuals sludge (40% by weight) and a soil (10% by weight) heat at 750°C for about one hour, was studied for its P sorption capacity. Langmuir and Freundlich sorption isotherms yielded similar relative maximum P sorption capacities for the sorbents. The results from the Langmuir calculations showed the following maximum P sorption capacities: 32.26 g P/Kg shells, 31.25 g P/Kg concrete waste, 7.19 g P/Kg alum residuals sludge, 290 mg P/Kg clay, 80 mg P/Kg kaolin, and 30 mg P/Kg mordenite. The P sorption capacity for the prepared ceramic material at grain size 12 mm was 4.85 g P/kg. This result suggests that the ceramic material could be used for P sorption while providing growth support for nitrifying bacteria, similar to the well documented a popular P sorption material: light expanded clay aggregate (LECA) from Sweden.

The chemical role of iron-bearing compounds on the dynamics of phosphorus in selected Brazilian latosols was investigated. The iron oxides were characterized in an attempt to assess their main chemical-mineralogical properties influencing the ion sorption mechanisms in those pedosystems. It was found that increasing total iron contents tend to increase the phosphorus adsorption capacity in the selected soils. 110 K-Mössbauer data reveal that the dominant iron oxides are hematite and goethite. Particularly for the yellower soil samples some prominent doublets, more certainly due to superparamagnetic relaxation, may be assigned to corresponding fractions of relatively small-sized particles.

This study aims to answer the question if temporary drawdowns could be a beneficial restoration measure for endangered Lobelia lakes. Intact littoral sediment cores with and without plants were used to simulate a drawdown over an almost 5 months period and a subsequent rewetting. During drawdown, the initial low saturation of sorption sites for phosphorus (P) increased due to increased contents of mobile P forms in the surface layers. Contents of P binding iron forms remained constant. The increase of mobile P forms was mostly derived from decayed plant material since the experimental set up caused dying of plants. Upon rewetting effluxes of total dissolved phosphorus and dissolved organic carbon were observed which are most likely attributable to the degraded plant material. A phosphorus uptake experiment with dried and rewetted sediment cores without plants showed that the initial high P binding capacity had been retained during drying and rewetting. These findings were confirmed by a small scale long-term drying (348 days) and rewetting (228 days) experiment which overall did not show a significant reduction in P adsorption capacity. Therefore, drawdowns can be an appropriate restoration measure for endangered Lobelia lakes given that the isoetid plants spread during the drying period. [ABSTRACT FROM AUTHOR]

Compared with soil testing phosphorus (STP), such as Olsen P, the degree of P saturation (DPS) generally improves the risk prediction for soil P loss. This study was conducted to assess various P sorption indices (PSI) to indicate P sorption maximum (Q max ) of soils, and their derived DPS indices as indicators of dissolved reactive P (DRP) concentration in soil leachate. A total of 236 intact soil columns were collected for leaching experiments from six major soil series in Ontario. By conducting the single-point isotherm, PSI-a of a given soil was determined as the amount of P sorbed by the soil during 24-h shaking in the 60 mg P L − 1 solution, PSI-b as the quotient of PSI-a/log C, where C is the solution P concentration after 24-h shaking, and PSI-c as the sum of PSI-a and Olsen P concentration. Among the tested PSIs, PSI-c gave the best prediction of Q max . Compared to Olsen P, soil DPS-1 (i.e. the quotient of Olsen P/PSI-c) improved the prediction of leachate DRP concentration. Moreover, soil pH did not impact the relationship of DPS-1 vs. soluble soil P loss. Based on the results from conditional probability analyses, Ontario soils were grouped into no risk, low risk, medium risk, and high risk categories. Considering that Olsen P is the current agronomic STP in Ontario and PSI-c can be quickly determined, soil DPS-1 can be used to identify leaching P loss and/or combined with site hydrology and P management practices for a more comprehensive soil P loss assessment. [ABSTRACT FROM AUTHOR]

Arctic streams are likely to receive increased inputs of dissolved nutrients and organic matter from thawing permafrost as climate warms. Documenting how Arctic streams process inorganic nutrients is necessary to understand mechanisms that regulate watershed fluxes of permafrost-derived materials to downstream ecosystems. We report on summer nitrogen (N) and phosphorus (P) uptake in streams draining upland soils from the Pleistocene, and lowland floodplain soils from the Holocene, in Siberia's Kolyma River watershed. Uptake of N and P differed between upland and floodplain streams, suggesting topographic variation in nutrient limitation. In floodplain streams, P uptake rate and uptake velocity were higher than N, while upland streams had similar values for all N and P uptake metrics. Phosphorus uptake velocity and size of the transient hydrologic storage zone were negatively related across all study streams, indicating strong influence of hydrologic processes on nutrient fluxes. Physical sorption of P was higher in floodplain stream sediments relative to upland stream sediments, suggesting more physically driven uptake in floodplain streams and higher biological activity in upland streams. Overall, these results demonstrate that high-latitude headwater streams actively retain N and P during summer base flows; however, floodplain and upland streams varied substantially in N and P uptake and may respond differently to inorganic nutrient and organic matter inputs. Our results highlight the need for a comprehensive assessment of N and P uptake and retention in Arctic streams in order to fully understand the impact of permafrost-derived materials on ecosystem processes, and their fate in continental drainage networks. [ABSTRACT FROM AUTHOR]

The phosphorus (P) efficiency of fertilised grazing systems on P deficient soils is often very low. P budgets (P input vs P output) were developed to examine P use in a long-term experiment in which grazing systems were managed with contrasting soil test P concentrations: (i) no P-fertiliser (P0; Olsen P = 2–5 mg/kg), (ii) near-optimum soil P fertility (P1; Olsen P = 10–15 mg/kg), (iii) supra-optimal P fertility (P2; Olsen P = 20–25 mg/kg), or (iv) with variable P fertility. Pastures were grazed with either 9 or 18 sheep/ha. P was exported as liveweight gain in sheep removed from the fields. Fertilised fields accumulated 89–93% of their P input over the whole P-budgeting period (1994–2006). However, this included P that was contributing to a “build up” in soil fertility (1994–2000). The efficiency of P fertiliser use was better demonstrated by P budgets during a soil P fertility “maintenance” phase (2001–2006) in which P inputs and soil test P concentrations of the grazing system treatments were relatively stable. When the amounts of P associated with the small changes in soil fertility were accounted for, the accumulation of P was 43–52 kg P/ha (83–87% of P inputs) in P1 fields and 87 kg P/ha (88% of P inputs) in P2 fields over the six-year period. Differences due to stocking rate were relatively small. Audits of the total P in sheep camp soil and field soil demonstrated that sheep camps were not a major sink for the P that was accumulating in the grazed fields. P was mainly accumulated in soil in the non-camp area of fields when they were fertilised and this was the major reason for low P-balance efficiency. It was concluded that the annual rate of P accumulation in fertilised soil (due mainly to P-sorption reactions) was higher when soil is being maintained at higher extractable-P concentrations. Consequently, strategies that can achieve equivalent pasture production with lower concentrations of extractable-P in the soil should reduce the amount of P fertiliser necessary for high production. [ABSTRACT FROM AUTHOR]

Sediment drying associated with large water level fluctuations is an increasingly common feature of temporary streams and lakes worldwide. Drying-induced sediment aeration and re-flooding periodically alter redox conditions, and therefore stimulate redox-sensitive processes influencing phosphorus (P) binding forms. We experimentally tested the effects of drying on P binding forms, and the P sorption potential, by drying and re-flooding lake sediments in the laboratory. Wet and dried fine sediments were re-flooded in columns, and the overlying water was continuously re-stocked to a constant P concentration. We measured changes in P forms, P uptake rates, and the pore water dynamics in each column over 36 weeks. Drying decreased the fraction of stable P, stimulated the mineralization of organic P, and increased the proportion of labile and reductant-soluble forms. Drying of sediment furthermore reduced its P sorption affinity and capacity by up to 32 % in batch equilibrium experiments, and led to a fourfold increase in sediment compaction which increased P uptake rates by a factor of 1.7 in sediment column experiments. Compaction due to drying also induced the development of a sharp gradient below which P was mobilized. These results indicate that in fine sediments, a single drying event can result in the transformation of P components into more labile forms which accumulate in the uppermost sediment layer, therefore raising the potential for a pulsed P release under reducing conditions. [ABSTRACT FROM AUTHOR]

Aluminum-based water treatment residuals (Al-WTRs) have a strong affinity to sorb P. In a proof-of-concept greenhouse column study, Al-WTR was surface-applied at rates equivalent to 0, 62, 124, and 248 Mg ha to 15 cm of soil on top of 46 cm of sand; Al-WTR rates were estimated to capture 0, 10, 20, and 40 years of P from an urban watershed entering an engineered wetland in Boise, ID, USA. Creeping red fescue ( Festuca rubra) was established in all columns; one set of columns received no Al-WTR or plants. After plant establishment, once per week over a 12-week period, ∼1.0 pore volumes of ∼0.20 mg P L were added to each column. Infiltration rates were measured, leachate was collected and analyzed for soluble P, and fescue yield, P concentration, and uptake were determined. After plant harvest, the sand, soil, and the Al-WTR layer were collected and analyzed for Olsen P; amorphous Al, Fe, and P; P storage capacity (PSC); and soluble + Al + Fe-bound, occluded, and Ca-bound P phases. Infiltration rate increased only due to the presence of plants. Leached P decreased (50 %) with plants present; Al-WTR further reduced soluble P leaching losses (60 %). Fescue yield, P concentration, and uptake increased with increasing Al-WTR rate, due to Al-WTR sorbing and potentially making P more plant available; Olsen-extractable P increased with increasing Al-WTR rate, supporting this contention. The PSC was reduced with the 62 Mg ha Al-WTR rate but maintained with greater Al-WTR rates. The 124 and 248 Mg ha Al-WTR rates also contained greater P associated with the soluble + Al + Fe and occluded phases which should be stable over the long term (e.g., decadal). It was recommended to apply Al-WTR near the 124 and 248 Mg ha rates in the future to capture urban runoff soluble P in the Boise, ID, engineered wetland. [ABSTRACT FROM AUTHOR]

Use of biochar has multiple benefits like C, soil organic matter stabilization, and agricultural productivity. However, there is limited information about the effect of biochar on P dynamics in acidic soils. Hence, we investigated the effects of fresh and aged hydrothermal coal produced from bark (HTC) and low temperature coal synthesized from sewage sludge (LTC) on the kinetics of P adsorption in a Ferralsol. The treatments comprised of a control, compost [7.7 g (kg soil)−1], hydrothermal carbonization coal [HTC, 2 g (kg soil)−1], low temperature conversion coal [LTC, 3.8 g (kg soil)−1], lime [0.3 g CaO (kg soil)−1], compost + HTC [3.8 + 1.0 g (kg soil)−1], compost + LTC [3.8 + 1.9 g (kg soil)−1, respectively], compost + lime [7.6 and 0.4 g (kg soil)−1, respectively]. The soil samples were incubated for a period of 3 months at 60% of the maximum water holding capacity. After 5 d and 3 months of the incubation period soil pH, Ca-acetate lactate (CAL) extractable soil-P, and P-adsorption isotherms were determined. The results show a significant effect of treatments on soil pH just after 5 d, which remained consistent after three months of incubation. All treatments, except HTC increased the soil pH compared with the control treatment. The maximum increase in soil pH was observed with compost + lime (from 4.5 to 6.1). The CAL-extractable P was significantly increased with application of LTC, compost + LTC, and compost + lime. The sorption parameters were not affected after 5 d of incubation. Due to residence effects, the P sorption capacity ( Sm) was significantly reduced in the LTC treatment [from 1182 to 1099 mg (kg soil)−1], and in the combination treatments compost + HTC [from 1182 to1078 mg (kg soil)−1], and compost + LTC [from 1182 to 1099 mg (kg soil)−1] treatments. The P binding energy (K) was significantly increased by the addition of LTC (from 2.18 to 4.26 mg L−1), lime (from 2.18 to 4.53 mg L−1), compost + HTC (from 2.18 to 7.03 mg L−1) and compost + LTC (from 2.18 to 4.68 mg L−1). Based on the results of the present study it is concluded that alone application of biochars do not alter the P bioavailability and sorption in a Ferralsol. However, combined application of biochars along with compost significantly decreases P sorption and increases bioavailability. [ABSTRACT FROM AUTHOR]

Redox reactions involving iron (Fe) strongly affect the mobility of phosphorus (P) and its migration from agricultural land to freshwater. We studied the transfer of P from groundwater to open drainage ditches in an area where, due to Fe(II) rich groundwater, the sediments of these ditches contain accumulated Fe oxyhydroxides. The average P concentrations in the groundwater feeding two out of three studied drainage ditches exceeded environmental limits for freshwaters by factors 11 and 16, but after passing through the Fe-rich sediments, the P concentrations in the ditch water were below these limits. In order to identify the processes which govern Fe and P mobility in these systems, we used diffusive equilibration in thin films (DET) to measure the vertical concentration profiles of P and Fe in the sediment pore water and in the ditchwater. The Fe concentrations in the sediment pore water ranged between 10 and 200 mg L −1 and exceeded those in the inflowing groundwater by approximately one order of magnitude, due to reductive dissolution of Fe oxyhydroxides in the sediment. The dissolved P concentrations only marginally increased between groundwater and sediment pore water. In the poorly mixed ditchwater, the dissolved Fe concentrations decreased towards the water surface due to oxidative precipitation of fresh Fe oxyhydroxides, and the P concentrations decreased more sharply than those of Fe. These observations support the view that the dynamics of Fe and P are governed by reduction reactions in the sediment and by oxidation reactions in the ditchwater. In the sediment, reductive dissolution of P-containing Fe oxyhydroxides causes more efficient solubilization of Fe than of P, likely because P is buffered by adsorption on residual Fe oxyhydroxides. Conversely, in the ditchwater, oxidative precipitation causes more efficient immobilization of P than of Fe, due to ferric phosphate formation. The combination of these processes yields a natural and highly efficient sink for P. It is concluded that, in Fe-rich systems, the fate of P at the sediment–water interface is determined by reduction and oxidation of Fe. [ABSTRACT FROM AUTHOR]

The sorption of phosphorus (P) was measured in calcareous paddy soils of Iran at room temperature as a function of pH and soil/solution ratio using batch experiments. Seven soils of different properties and five soil/solution ratios, 1:10, 1:25, 1:50, 1:100, 1:150, and eight pHs, 2, 3, 4, 5, 6, 7, 8, 9 were employed for this study. The pH value of these seven soil samples was adjusted to cover a range of 2-9 by addition of 1 M HCl or 1 M NaOH. The sorption of P was affected by the soil solution pH; at low pH the sorption of P was high. The soil/solution ratio was found to have significant effect on the sorption of P. A larger soil/solution ratio, i.e., more soil for a constant mass of solution, resulted in a smaller maximum P sorption value. This result also held true for Freundlich distribution coefficient at most studied pHs. There were significant correlations between P sorption and Freundlich distribution coefficient and pH and soil/solution ratio. The equations obtained can be used to predict the solubility of P and Freundlich distribution coefficient as a function of pH and soil/solution ratio in calcareous paddy soils. [ABSTRACT FROM AUTHOR]

Despite the ability of fly ash (FA) to remove phosphorus (P) from water via sorption and precipitation, its use as a bedding material for planted floats has never been evaluated. This study was conducted to investigate the effects of FA on P removal and chlorophyll- a (an indicator of algal growth) reduction in P-contaminated water. Six different FA rates (0, 2.5, 5, 10, 25, and 50 w/w%; codes are FA 0 , FA 2.5 , FA 5 , FA 10 , FA 25 , and FA 50 , respectively) and two rice ( Oryza sativa L.) treatments (unplanted and planted) were investigated. The floats containing FA were placed on P-enriched (4 mg P L −1 ) baths. Water samples were collected periodically and analyzed for the concentrations of total P (TP), soluble P (SP), and chlorophyll- a . Both SP and TP decreased ( P < 0.05) as FA rate increased, and rice planting further enhanced ( P < 0.05) P removal. The first-order rate constants of TP decrease in FA 50 (0.143 and 0.192 day −1 for rice unplanted and planted, respectively) were two-fold greater than those (0.072 and 0.090 day −1 , respectively) in FA 0 . Regardless of rice planting, chlorophyll- a concentration in the treatments with FA at 0–10% increased rapidly up to 0.65 mg L −1 within 10 days after treatment; however, those in FA 25 and FA 50 were consistently lower than 0.05 mg L −1 , indicating suppression of algal growth, probably due to enhanced P removal by FA. However, increased salinity by FA mixing might further contribute to the suppression of algal growth. [ABSTRACT FROM AUTHOR]

Abstract: Phosphorus (P) is a limiting nutrient in many aquatic systems. The bioavailability of P in natural waters strongly depends on its speciation. In this study, structural properties of iron colloids were determined and related to their effect on P sorption and P bioavailability. The freshwater green alga Raphidocelis subcapitata was exposed to media spiked with radiolabelled 33PO4, and the uptake of 33P was monitored for 1 h. The media contained various concentrations of synthetic iron colloids with a size between 10 kDa and 0.45 μm. The iron colloids were stabilised by natural organic matter. EXAFS spectroscopy showed that these colloids predominantly consisted of ferrihydrite with small amounts of organically complexed Fe. In colloid-free treatments, the P uptake flux by the algae obeyed Michaelis–Menten kinetics. In the presence of iron colloids at 9 or 90 μM Fe, corresponding to molar P:Fe ratios between 0.02 and 0.17, the truly dissolved P (<10 kDa) was between 4 and 60% of the total dissolved P (<0.45 μm). These colloids reduced the P uptake flux by R. subcapitata compared to colloid-free treatments at the same total dissolved P concentration. However, the P uptake flux from colloid containing solutions equalled that from colloid-free ones when expressed as truly dissolved P. This demonstrates that colloidal P did not contribute to the P uptake flux. It is concluded that, on the short term, phosphate adsorbed to ferrihydrite colloids is not available to the green alga R. subcapitata. [Copyright &y& Elsevier]

Abstract: Phosphorus (P) is a scarce, nonrenewable resource; its acquisition by plants decreases when soil moisture declines, as anticipated under future climate-change scenarios. It is, therefore, important to understand plant responses and adaptations to dual moisture and P limitations, in order to maintain crop productivity and predict plant performance in natural ecosystems. We review current knowledge of the effect of simultaneous water and P shortage on plant function, and identify key knowledge gaps. Plants have developed a range of adaptations to ensure P uptake is adequate to maintain vital functions within a broad range, at least until a certain level of P and/or drought stress is exceeded. Differences in plant growth and amount of P taken up under dual moisture and P limitations greatly depend on the rate of soil drying and wetting, the severity and duration of drought cycles, plant uptake capacity, root system plasticity, presence and magnitude of hydraulic redistribution, P-resorption ability, and soil properties such as waterholding capacity, P diffusion rate, P mineralization and fixation rates, and the activity of arbuscular mycorrhizal (AM) symbioses. During the process of soil drying, both P fertilization and association with AM fungi may increase performance under drought, until a certain level of water stress is exceeded. A small number of previously reported contradictory results probably reflect differences/limitations in experimental approaches. When breeding crop varieties to increase the efficiency of P and water acquisition, and when examining performance of species in natural ecosystems, multiple and interacting processes, from the scale of cellular to whole plant, must be considered. [Copyright &y& Elsevier]