Phosphate Fixation Research Articles

Goat manure application improves phosphate fertilizer effectiveness through enhanced biological cycling of phosphorus

High phosphate fixation necessitates the application of high rates of phosphorus (P) fertilizers to achieve reasonable crop yields in most tropical soils. The present study investigated the efficacy of goat manure in improving the effectiveness of fertilizer P for increasing maize yields. Treatments consisted of combinations of four rates of goat manure (0, 2.5, 5 and 10 g kg)−1 equivalent to 0, 5, 10 and 20 t goat manure ha)−1, respectively) and four rates of inorganic P (0, 45, 90 and 180 mg P kg)−1 equivalent to 0, 90, 180 and 360 kg P ha)−1, respectively) applied to 7 kg soil in pots. Maize (Zea maize L.) was sown immediately after application. Maize dry matter yields (maize yield) and the concentrations of resin P, soil microbial biomass P (biomass P), 0.5 mol L)−1 NaHCO3 extractable inorganic P (NaHCO3-Pi) and 0.1 mol L)−1 NaOH extractable inorganic P (NaOH-Pi) were determined 6 and 12 weeks after planting. After 12 weeks, maize yield increased with the addition of fertilizer P or goat manure separately and was further increased when they were applied together. These synergistic effects on maize yield were ascribed to enhanced P cycling because goat manure increased the concentration of biomass P, which in turn accounted for most of the observed variations (63%) in maize yield. The combination of biomass P and resin P, however, explained a greater proportion of the variations in maize yield (73%), suggesting that the usefulness of biomass P as an index of P availability would be enhanced if used in conjunction with resin P. These results indicated that goat manure application could be used to increase soil microbial biomass P, which in turn could improve the effectiveness of fertilizer P in the Eastern Cape, South Africa.

Sustainable Management of Dryland Alfisols (Red Soils) in South India

A community based cooperative research project was implemented on farmers' fields on some dryland Alfisols in Tamil Nadu, India, to demonstrate and validate improved dry-farming technologies, such as: 1) soil and water conservation and water harvesting; 2) cropping systems, including intercropping and double cropping; 3) recycling of processed agricultural wastes and byproducts; and 4) low-cost drip irrigation. Disc plowing to 30 cm depth during summer and contour bunding enhanced soil moisture storage in the profile, and facilitated harvesting of runoff water into a community pond. Under the bimodal rainfall pattern in the region, among the medium- and long-duration varieties of pigeon pea, short-duration varieties of blackgram and greengram evaluated, long-duration variety of pigeon pea was the most suited to this region. The pigeon pea variety ‘VBN2’, blackgram variety ‘VBN3’, and greengram variety ‘VBN2’ produced the maximum grain yields. Increasing the land equivalent ratio (LER) by intercropping of pigeon pea with pulses and oilseeds enhanced agronomic productivity. Pigeon pea + groundnut was the best intercropping system. Pigeon pea + lablab and pigeon pea + groundnut intercropping system produced the highest yields. In years with normal rainfall, green manuring with sunnhemp and raising a pulse crop, horsegram, increased soil fertility. Application of compost enriched with rock phosphate (produced by using locally available crop residues of cotton, pigeon pea, sugarcane, and raw pressmud) significantly enhanced the yield of pigeon pea, groundnut, onion, and okra in these degraded Alfisols with high phosphate fixation capacity. Tied ridging and mulching with groundnut residues produced the maximum yield of cowpea even in seasons with below normal rainfall. Tied ridging produced the highest net returns from pigeon pea + greengram intercropping system. A low-cost, zero-energy drip-irrigation system produced the highest yield of 23.2 Mg/ha of tomato, with a saving in water of 73.8% compared with the control. Introduction of arid horticulture with amla, sapota, and mango, and water management through pitcher-pot irrigation and mulching with coconut husk as a means of diversification of land use management, provided employment during the off-season and enhanced household income.

The Solubility Constant of Variscite

Only a few studies have been made on the ion product of variscite, Al(III) phosphate dihydrate, AlPO4·2H2O, a parameter of fundamental importance in clarifying the fixation of soluble phosphates in acid soils. The solubility of variscite in H3PO4 solutions of molality ranging from 1 × 10−4 to 0.1 mol kg−1 was determined at 25°C. The data were explained with a value of the ion product equal to 10−3.14 mol−1 kg (at the infinite dilution reference state) and assuming the formation of complexes AlPO4(aq), AlHPO4+, and Al(H2PO4)2+ The solubility product obtained in this work differs by orders of magnitude from the literature values. The discrepancies are mainly due to the use of solids of different composition as well as to the assumption of the Al3+ ion as the unique soluble Al species. On the basis of equilibrium constants, the fixation in acid soils of soluble phosphates implicates the formation of variscite, while only at higher concentrations does the fixation occur as strengite.

Some Structural and Electronic Features of the Interaction of Phosphate with Metal−Humic Complexes

Previous studies demonstrated the formation of stable phosphate-metal-humic complexes in solution. These studies, however, indicated that the proportion of complexed metal that intervenes in phosphate fixation is rather low. In this study we investigate the possible structural and electronic features of the binding site involved in phosphate fixation in metal-humic complexes that could explain this fact. To this end, we have studied phosphate-metal-humic complexes involving Fe(III), Al(III), and Zn(II) using three complementary techniques: infrared spectroscopy (FTIR), fluorescence, and molecular modeling. The FTIR study indicated that, in the case of those complexes involving Fe and Zn phosphate, fixation is associated with a stabilization of the metal-carboxylate bond. In the case of Al this effect is less clear. This effect of phosphate fixation on the characteristics of the metal-humic binding site was also supported by the results obtained in the Fluorescence study, which showed significant changes in the quenching effect normally associated with metal complexation in humic substances upon phosphate fixation. Finally, the molecular modeling study revealed that the stability of phosphate-metal-humic complexes is inversely related to the stability of the metal-humic interaction. This result could explain why only a relatively low proportion of humic complexed metal is involved in phosphate fixation.

Fixation of porous calcium phosphate with expanded bone marrow cells using an autologous plasma clot

AbstractMultipotent human mesenchymal stromal cells (hMSCs) are currently the most promising cell type for regenerative medicine and tissue engineering. For clinical applications with special focus on fracture repair a method to deliver in vitro‐expanded bone marrow cells to the fracture site is presented. Autologous blood plasma clotting was used to fix expanded cells and synthetic tricalcium phosphate particles. A jelly‐like but solid composite matrix was obtained which could easily be handled by the surgeon. The majority of embedded cells remained viable after the plasma gelation process, as was determined by fluorescence microscopy. Experimental cell culture over a period of 15 days showed proliferating mesenchymal stromal cells within the plasma clot.

Retenção e dessorção competitivas de ânions inorgânicos em gibbsita natural de solo

O objetivo deste trabalho foi quantificar a retenção e a dessorção competitivas dos ânions nitrato, sulfato, silicato e fosfato na fração argila gibbsítica de um Gleissolo Melânico. Amostras da fração argila foram agitadas em tubos de centrífuga com solução de NaCl 30 mmol c L-1 contendo estes ânions em quantidades equivalentes a 30% das respectivas capacidades máximas de retenção exibidas pela argila. Para fins comparativos, as amostras foram agitadas com a mesma solução contendo 1 mmol c L-1 de cada um dos ânions citados. Os tubos foram centrifugados e determinaram-se as concentrações aniônicas nos sobrenadantes. A dessorção foi realizada agitando-se a fração argila remanescente nos tubos de centrífuga com a solução de NaCl, quantificando-se os ânions liberados. Em outro ensaio, com o silício e o fósforo previamente adsorvidos à gibbsita, adicionou-se, na seqüência, o fósforo e o silício intercalados para avaliar a capacidade de dessorver o ânion previamente adsorvido. O fosfato foi preferencialmente adsorvido em relação aos demais ânions estudados e a aplicação prévia de silício reduziu a fixação de fosfato. Desse modo, a aplicação de silício previamente à de fósforo favorece a fitodisponibilidade deste em solos altamente intemperizados.

Zur Phosphatfixierung in sächsischen Verwitterungsböden auf den Ergussgesteinen Nephelinbasalt, Phonolith und Diabas

Investigated Saxonic brown soils (Cambisols) on nephelinbasalt, phonolith and diabase in a considerable extent are able to remove water soluble phosphate to a form, which is not double lactate soluble and not available for plants. With regard to this property these soils show a strong phosphate fixation. However, measure of phosphate fixation of soils–ratio of hydrochloric acid soluble phosphorus (P-HCl) and double lactate soluble phosphorus (P-DL) – is different depending on specific weathering rock. Soils on nephelinbasalt are marked by very high ratios and reach values of 36 to 166. They distinguish from soil on phonolith with ratio 15 and soils on diabase with ratios in the range of 9 – 21. Differences between intensities of phosphate fixation possibly can be caused by different mineralogical compositions of weathering rocks and soils and their specific ability of weathering depending on their crystal structure and resulting in different intensities of weathering by soil minerals. Correlation between phosphate fixation and intensities of weathering by soil minerals especially is demonstrated by soils on nephelinbasalt showing strong phosphate fixation and simultaneously higher contents of weathering products of oxalate and dithionite soluble iron and “free” aluminium (by Foster). For minimizing phosphate fixation, arable soils should be regulated to optimal pH and manuring of phosphate should be given each year and, if possible, nearby the roots of plants.

Role of fulvic acids for transporting and fixing phosphate and iron ions in bean plants by radiotracer technique

Among humic substances formed by organic matter decomposition process, fulvic acids have been extensively studied because their solubility and soil fertilizer properties. This paper describes how some mineral nutrient elements are absorbed by the root as well as the foliage of bean plants and how they move in both directions depending on their association to fulvic acids. In this study, radiotracers of phosphate and iron have been used (H232PO4-, 59Fe2+). The results obtained are quantitative by instrumental detection and qualitative by autoradiography of the radiotracers. A very clear effect has been found about motion and fixation of phosphate and iron ions in bean plants brought about by fulvic acids commercially produced in Mexico by organic synthesis. This effect seems to be the more homogeneous distribution in the vegetable tissues of the mineral ions absorbed from the soil.

Estimating the precipitation potential in urine-collecting systems

Precipitation in urine-separating toilets (NoMix toilets) and waterless urinals causes severe maintenance problems and can strongly reduce the content of soluble phosphate. In this study, we present a computer model for estimating the precipitation potential (PP) in urine-collecting systems. Calculating the PP enables to predict the composition and mass concentration of precipitates. We used our computer model for investigating how urea hydrolysis and dilution with flushing water affect precipitation. In a previous study, we found that microbial urea hydrolysis (ureolysis) triggers precipitation and that the amount of precipitates is limited by calcium and magnesium. With the present simulations, we could confirm these findings. We determined that only a small fraction of urea has to be hydrolysed for reaching 95% of the maximum PP. Since urease-positive bacteria are abundant in urine-collecting systems, strong precipitation is very likely. In further simulations, we determined that struvite (MgNH 4PO 4·6H 2O) and hydroxyapatite (HAP, Ca 10(PO 4) 6(OH) 2) are the main precipitate compounds. If urine is highly diluted with tapwater, calcite (CaCO 3) occurs as well. HAP is the only calcium phosphate mineral, although several others were supersaturated. Additionally, the simulations indicated that urine dilution diminishes the risk of blockages, since the mass concentration of precipitates decreases with the volume of flushing water. Rainwater flushing is more effective than flushing with tapwater. Moreover, flushing with tapwater leads to high phosphate fixation, because the total amount of calcium and magnesium ions increases, while the total amount of phosphate keeps constant. Finally, we compared simulation results with field measurements and found good agreement at low and very high urine dilution.

Refixation of Phosphates Released During Bio-P Sludge Handling as Struvite or Aluminium Phosphate

Phosphate release and phosphate fixation during sludge treatment of waste activated sludge was investigated with a pilot plant for enhanced biological phosphorus removal, complemented by laboratory investigations of sludge samples from different large enhanced biological phosphorus removal plants. The major part of the eliminated phosphorus in the pilot plant was due to the storage of polyphosphate in the waste activated sludge and was accompanied by an uptake of magnesium and potassium. Stabilising waste activated sludge from the enhanced biological phosphorus removal pilot plant results in a hydrolysis of polyphosphate. As a result of polyphosphate hydrolysis in stabilising systems, phosphate, magnesium and potassium are released, but only potassium remains in solution whereas magnesium and a part of the released phosphate was precipitated as struvite. Another large fraction of the released phosphate was fixed by participation of aluminium.

Multi-media-layering system for food service wastewater treatment

Domestic wastewater treatment was studied using the Multi-Media-Layering (MML) system. There are two MML units in the system for alternative use. Each unit has 1.0×2.0×1.5 m internal dimensions. One unit is composed of soil mixed with sawdust plus iron scraps at a ratio of 75:10:15 by weight; the other is composed of soil mixed with (kenaf plus corncob) plus iron scraps at the same ratio as the first unit. The mixture layers are arranged in a ‘brick like’ pattern. Each block is 0.08 m thick and filled in a concrete box. Charcoal of 0.02 or 0.03 m thickness was put on the top of the mixture layer. Zeolite was inserted between the blocks (0.05 m thick) to prevent clogging. Air is supplied through porous pipes installed at the middle layer of the MML unit. The system was tested using toilet wastewater from Kasetsart University’s cafeteria. For this experiment, the wastewater was discharged to the two concrete boxes simultaneously about 460 l day −1. The wastewater and treated water were collected every 2 weeks for chemical analysis. The results revealed that the removal percentage of suspended solid, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total N, NH 4-N, total P and dissolved P were 53, 48, 58, 68, 53, 52 and 64, respectively for a media mixture of sawdust plus iron scraps. When aeration was applied for 24 h, at 50 l min −1 for 14 days, the efficiency of wastewater treatment increased significantly. The percentage removal of suspended solid, BOD, COD, total N, NH 4-N, total P and dissolved P was 71, 90, 70, 91, 76, 90 and 89 by sawdust with a loading rate of 230 l m −2 day −1. Kenaf plus corncob was less effective compared to sawdust. Aeration assists decomposition of BOD, COD and suspended solid as well as phosphate fixation. The MML system was more effective than the current system used at the Department of Soil Science.

Chemical retardation of phosphate diffusion in simulated acid soil amended with lignosulfonate

The availability and movement of inorganic phosphate fertilizer is usually low due to precipitation and adsorption reactions in soil. Lignosulfonate (LS), which is produced from acid sulfite pulping processes, has similar characteristics to soil organic materials. An experiment was designed to study the effects of LS on P movement in a simulated acid soil containing aluminum-saturated cation exchange resin and acid-washed fine sand. The resulting simulated soil had a cation exchange capacity of 22 cmolc kg−1 and either no or 10 g kg−1 gibbsite. Movement of surface-applied monopotassium phosphate was studied in soil columns, either with 20 g kg−1 LS or without LS. Lignosulfonate reduced phosphate fixation and sustained a higher water extractable phosphate concentration near the surface of the columns, but had no effect on downward phosphate movement in the columns with gibbsite. Lignosulfonate reduced the solution concentration of P near the surface and reduced downward phosphate movement in the columns without gibbsite. The resin-sand column with gibbsite closely reflected an acid soil, and this research showed that adding LS would increase fertilizer P availability in a gibbsite-rich acid soil. Adding Ca-LS to Al-rich soil is beneficial for another reason, improving Ca nutrition, which is poor for these soils. Key words: Chemical retardation, phosphate diffusion, lignosulfonate amendment

Kinetics of phosphate sorption by goethite‐ and bentonite‐goethite (b‐g) system

The study of phosphate (PO4) fixation due to reactions which occur to the surface of soil minerals has been limited by a lack of evidence on which a structural model may be based. A structural model should attempt at least to describe the coordination on the absorbed PO4 3‐ ion, that is, to indenfity the immediate neighbour atoms or ions in contact with it. Many kinetic equations have been used either to deduce the mechanisms or simply to summarise results of this continued removal of PO4 from solution. In this study five kinetics models of first‐order, Elovich, parabolic diffusion, modified Freundlich and a new kinetic equation, were evaluated to describe the rate of PO4 sorption from synthetic goethite and bentonite‐goethite (b‐g) system into 0.01 M calcium chloride (CaCl2) solutions of 0.0403–0.4435 mmol P L‐1. The rate of PO4 sorption is a dynamic factor that regulates the continuous supply of PO4and was found initially to be rabid but gradually declined with time. The adsorption of PO4 per gram of goethite was faster and greater than the adsorbed amount of PO4per gram of bentonite‐goethite system. Comparison of the coefficients of determination (r) indicates that Elovich, Freundlich, and the new kinetic models provided better fits for phosphate sorption by goethite while First order, Parabolic, and Freundlich were found to be the best for bentonite goethite (b‐g) system.

Agronomic measures for better utilization of soil and fertilizer phosphates

Global known phosphate deposits are a finite resource which will run out in about four centuries at the present consumption rate. Since about 90% of the phosphate mined is used for fertilizer, soil and fertilizer phosphate should be efficiently used. Various agronomic measures are discussed relevant for saving phosphate and avoiding losses. Phosphate fertilizer rates should be adjusted to measured requirements for phosphate using soil tests. Particularly in areas with high livestock intensities soils frequently are much enriched in available phosphate and do not need further phosphate application whether in organic or in inorganic form. Excessively high levels of available soil phosphate, much higher than required for optimum crop production increase the hazard of phosphate loss by wind and water erosion and even leaching. Loss of plant available phosphate in soils occurs by phosphate fixation which is especially strong in acid mineral soils. Such losses can be dramatically reduced by liming soils to a pH of 6–7. In tropical areas where lime frequently is not available row placement of phosphate fertilizer is recommended. Oxisols with a very low pH liming, however, may promote phosphate fixation due to the formation of phosphate adsorbing Al complexes. Biological assimilation of phosphate may prevent inorganic phosphate from fixation by soil particles. Organic anions produced during the decomposition of organic matter in soils as well as the excretion of anions by plant roots depress phosphate adsorption by competing with phosphate for binding sites at the adsorbing surface. Hence farming systems and rotations which bring much organic matter into soils contribute to a better use of soil and fertilizer phosphate. Mycorrhization of plant roots with appropriate fungi ecotypes may essentially improve the exploitation of soil phosphates. The choice of the appropriate phosphate fertilizer type is crucial for its efficient use. This applies particularly for apatitic fertilizers of which the availability is poor in weakly acid to neutral and calcareous soils.

Surface Charge Characteristics of Alfisols and Inceptisol and the Changes on Phosphatization

Three surface soil samples (0-1.15 m) were collected from different locations of West Bengal, India, namely, Jhargram (Alfisol), Bolpur (Alfisol), and Mohitnagar (Inceptisol) having contrasting physicochemical properties. The charge characteristics of the clay fraction of these soils were probed in terms of the zero-point of charge (ZPC) of the soils. The high values of ZPC noted for the Jhargram and the Bolpur soils may be due to the presence of a large amount of free (variable-charge) sesquioxides in these soils; lower ZPC values were noted in the Mohitnagar soil. Furthermore, the negative magnitudes of ΔpH [pH (KCl) - pH (H 2 0)] values, noted for the present soils, suggested that the Mohitnagar soil had less developed characteristics, whereas the Jhargram and the Bolpur soils were in more advanced stages of pedogenic development. The soil samples studied for ZPC were also treated with aqueous KH 2 PO 4 solution, and the ZPC values of these phosphate-treated soil samples registered shifts to lower pH values. This may have arisen from an increase in negative charge on soil colloids, following ligand exchange with the added phosphate. The surface potential and the surface charge density of each soil were found to increase in negative magnitude on phosphate application, possibly due to concomitant increases of the negative charges of the clay fraction of the given soils on phosphate fixation through ligand exchange mechanism. The implication of the above parameters, especially their changes on phosphate treatment of the soils, have been related to the tendency of the given soils to immobilize the added phosphate.

Behavior of waste activated sludge from enhanced biological phosphorus removal during sludge treatment

Phosphate release and phosphate fixation during sludge treatment of waste activated sludge (WAS) was investigated with a pilot plant for enhanced biological phosphorus removal (EBPR), complemented by laboratory investigations of sludge samples from different large EBPR plants. The major part of the eliminated phosphorus in the pilot plant was due to the storage of polyphosphate (poly‐P) in the WAS and was accompanied by an uptake of magnesium and potassium. Thickening and stabilizing WAS from the EBPR pilot plant results in a hydrolysis of poly‐P which could be modeled with first‐order kinetics and the Arrhenius relationship for the temperature dependence of the reaction constant. As a result of poly‐P hydrolysis in stabilizing systems, phosphate, magnesium, and potassium are released, but only potassium remains in solution, whereas magnesium and a part of the released phosphate were precipitated as struvite. Another large fraction of the released phosphate was fixed by aluminium.

P-fixation by Mg, Ca and zeolite a during stabilization of excess sludge from enhanced biological P-removal

In anaerobic digestion of excess sludge originating from enhanced biological phosphorus removal (EBPR) a complete hydrolysis of polyphosphate occurs. Varying information exists about the resulting return flow of phosphorus to the activated sludge plant. Magnesium, calcium and zeolites from detergents are the main species involved in the refixation of dissolved phosphate in the digester supernatant. Their interactions and mechanisms of phosphate removal have been characterized and quantified in experiments. The precipitation of struvite (MgNH4PO4·6H2O) evolves according to the equilibrium, whereas the fixation by calcium occurs kinetically controlled in the form of brushite (CaHPO4·2H2O) or hydroxyapatite (Ca5(PO4)3OH). Zeolites in digester sludge originate mainly from detergents. They represent around 7% of total solids entering the digester and their impact on digestion is given by 4 modes: The control of free cation concentrations as an exchanger, as a source for calcium ions, as generator of aluminum phosphate precipitation after being partly hydrolyzed and as a nucleus for crystallization processes. With the current sludge composition phosphate fixation processes in anaerobic digesters avert serious recycle load problems.

Kinetics of phosphorous sorption by hematite and bentonite‐hematite (b‐h) system

Abstract The study of phosphate (P) fixation due to reactions which occur to the surfaces of soil minerals has been limited by a lack of different evidence on which a structural model may be based. A structural model should attempt at least to describe the co‐ordination of the adsorbed P ion, that is, to identify the immediate neighbor atoms or ions in contact with it. The kinetics of P adsorption from solution to exchangeable phases was investigated on hematite (h) and bentonite‐hematite (b‐h) system. Phosphate adsorption time was evaluated on the above samples using 1250, 2500,3750,5000, 7500 and 13500 μg P/L solutions equilibrated from 1 to 110 days. Equilibrium in P exchange reached faster in hematite than in bentonite‐hematite system. First order, Parabolic Diffusion, Elovich, modified Freundlich models, but also a new kinetic model applied on analytical data. Freundlich and the new kinetic model were found to describe P sorption for both examined samples, while Parabolic Diffusion and First order ki...

P-fixation by Mg, Ca and zeolite a during stabilization of excess sludge from enhanced biological P-removal

In anaerobic digestion of excess sludge originating from enhanced biological phosphorus removal (EBPR) a complete hydrolysis of polyphosphate occurs. Varying information exists about the resulting return flow of phosphorus to the activated sludge plant. Magnesium, calcium and zeolites from detergents are the main species involved in the refixation of dissolved phosphate in the digester supernatant. Their interactions and mechanisms of phosphate removal have been characterized and quantified in experiments. The precipitation of struvite (MgNH4PO4•6H2O) evolves according to the equilibrium, whereas the fixation by calcium occurs kinetically controlled in the form of brushite (CaHPO4·2O) or hydroxyapatite (Ca5(PO4)3OH). Zeolites in digester sludge originate mainly from detergents. They represent around 7% of total solids entering the digester and their impact on digestion is given by 4 modes: The control of free cation concentrations as an exchanger, as a source for calcium ions, as generator of aluminum phosphate precipitation after being partly hydrolyzed and as a nucleus for crystallization processes. With the current sludge composition phosphate fixation processes in anaerobic digesters avert serious recycle load problems.

Competitive sorption of phosphate and marine humic substances on suspended particulate matter

The sorption behavior of dissolved orthophosphate in the presence of background organics has been evaluated by studying the sorption on suspended particles (sand, calcite, bentonite and iron oxide). Humic and fulvic acids, that are the most significant component of organic substances in aquatic systems, were used as competitive solutes. Marine humic substances were isolated from the surface part of the sediment collected in Raska bay, Adriatic sea. Since the phenomena of phosphate fixation are especially important in estuarine waters, when fresh and saline waters undergo mixing in the coastal zone, the influence of salinity was studied. It was found that the following effects could be considered: - reduced phosphate fixation due to favorable sorption of humic substances onto suspended particles, - enhanced sorption induced by increased salinity and concentration of Ca2+-ions which enabled the bridging between sorbed humic acids and phosphate.