Phosphate Sorption In Soils Research Articles

Does the carbon skeleton of biochar contribute to soil phosphate sorption? A case study from paddy soils with woody biochar amendment

Context The phosphorus (P) sorption capacity of biochar and the effects of biochar amendment on soil P sorption and availability remain uncertain. Aims This study determined the specific contributions of the biochar inorganic component (mineral ash) and its carbon skeleton to the P sorption capacity of biochar. Methods A woody biochar and its acid-washed counterpart were added to two types of paddy soils with two P-retention capacities: high P sorption (HPS) and low P sorption (LPS). Key results Washing biochar with HCl solution drastically decreased the concentrations of calcium, magnesium, iron (Fe), and aluminium (Al) in the biochar. However, Fourier transform infrared and X-ray photoelectron spectroscopy spectra indicated that the washing procedure did not decrease the biochar organic carbon content and its surface functional groups. Acid-washed biochar showed nearly zero P sorption after 24 h of equilibration with P solution, and its incorporation had little effect on P sorption of the two paddy soils. Amendment with original alkaline woody biochar tended to increase P sorption capacity of LPS soils, but decreased that of HPS soils. The variations in Langmuir P sorption maxima, an indicator of soil P sorption capacity, among the soils and biochar treatments could be primarily explained by the amorphous Fe and Al concentrations, which indicates that the effect of biochar addition on soil P sorption was highly dependent on intrinsic soil P-retentive properties. Conclusion These results demonstrate that the biochar carbon skeleton had a very limited contribution to biochar P-retention capacity. Implications Our results suggest that the application of aged biochar with lower mineral contents to humid acidic highly weathered soils will have limited P retention capacity.

Biochar-induced soil phosphate sorption and availability depend on soil properties: a microcosm study

The effects of soil properties on biochar-induced soil phosphate sorption and availability are not well investigated. An alkaline biochar-induced soil phosphate sorption, phosphorus (P) availability, and related mechanisms (including the effects of calcium/magnesium (Ca/Mg) minerals in biochar and the liming effect) in different soils were studied in the laboratory. Two soils (sandy soil and clay soil) with contrasting P-retention capacities were amended with four rates of alkaline peanut biochar. Soil phosphate sorption–desorption indices were characterized by a multiple-point isotherm batch experiment. Soil P availability was determined by sequential fractionation method. The alkaline biochar addition increased the phosphate sorption of sandy soil but decreased the phosphate sorption of the clay soil. The interaction between the biochar and external phosphate on the biochar surface was mainly controlled by adsorption process, rather than precipitation. The liming effect of the biochar decreased the Langmuir phosphate sorption maxima (Smax) of clay soil. However, the biochar increased Smax of clay soil when the liming effect was eliminated, because Ca/Mg minerals in biochar can provide phosphate sorption sites. The dominant P fraction of the biochar was Ca-bounded P, and therefore the biochar addition increased HCl-extractable P of both sandy and clay soils. Generally, the biochar addition increased P availability of clay soil because it increased NaHCO3-extractable P content and decreased phosphate sorption. P mobility of sandy soil was also increased by biochar addition, because water-extractable P and EPC0 were increased. Our results suggest that both the biochar (particularly the contents of Ca/Mg minerals within) and soil properties (particularly the initial phosphate sorption capacity) determine phosphate sorption and availability following the biochar application. The alkaline biochar application to sandy soils with low P buffering capacity should consider the amount of P input from biochar and the corresponding environmental risk, although biochar addition can enhance phosphate sorption in these soils in the short term.

Use of biochar as a possible means of minimizing phosphate fixation and external P requirement of acidic soil

Phosphate fixation is a main factor limiting phosphate availability and reducing crop production in acidic soils. Although biochar addition has been suggested as a means of ameliorating acidic soils, questions remain about the impacts of biochar on phosphate fixation and availability in these soils. To address these questions, a biochar produced from sugarcane bagasse was added at four different levels (0, 1, 3, and 6% w/w) to an acidic soil. After 30 days of incubation, comparisons were made between the chemical properties of the biochar-amended soils and those of the original one. Sorption isotherm experiments were also conducted to estimate soil phosphate sorption capacity and affinity parameters under biochar amendment. Results showed that biochar application improved such soil chemical properties as pH and cation exchange capacity as well as exchangeable calcium, magnesium, sodium, and potassium cations. Biochar was also observed to increase phosphate sorption capacity of the soil but reduce its phosphate sorption strength, indicating that biochar-amended soils were potentially able to fix lower amounts of phosphate than the original acidic soil was. Moreover, soil phosphate buffering capacity indices decreased as a result of biochar incorporation, indicating the easier release of phosphate from the solid to the solution phase in biochar-amended soils. Biochar addition was also observed to reduce effectively (up to 62%) the standard phosphorus requirement of the soil. In conclusion, biochar amendment was found to induce positive changes in phosphate sorption properties of acidic soils, thereby providing conditions more favorable to plant growth through sufficient phosphate availability.

Soil Phosphate Sorption Characteristics of Selected Calcareous Soil Series of Southern Punjab, Pakistan

To estimate the sorption and desorption capacity of some selected calcareous soils Jhatpat, Miani Pacca and Hadhwar from southern Punjab in Pakistan were analyzed. The sorption isotherms of the three soils yielded different curves. The maximum sorption was recorded in the Miani pacca soil series with value of sorption 201. 23 mg kg-1 which was followed by the Hadhwar series with peak sorption value of 190.04 mg kg-1. The lowest value for sorption was determined in the Jhatpat soil series. Comparing the different models (Langmuir, Freundlich and Temkin), Freundlich model showed good fit to the sorption isotherms with regression coefficient (R2) having value of 0.99, 0.99 and 0. 98 for Jhatpat, Miani pacca and Hadhwar soil series respectively, which was higher than the other two models used. The study on the effect of equilibration time (1, 10, 30 and 60 days) of applied inorganic Phosphatic fertilizers i.e. Single super phosphate (SSP) and diammonium phosphate (DAP) @ 60 and 120 kg ha-1 on two soil series with highest P sorption. The P sorption increased with increase in the time of equilibration, with higher value of extractable P was found 22.246 mg P kg-1 after 1 day of incubation, and it gradually decreased with the lowest value of 8.271 mg kg-1after 60 days of incubation.

Effectiveness of a rock phosphate solubilizing fungus to increase soil solution phosphate impaired by the soil phosphate sorption capacity

Available phosphate (P) deficiency in tropical soils has been recognized as a major factor that limits soil quality and plant performance. To overcome this, it is necessary to add high amounts of soluble P-fertilizers; however, this is inefficient and costly. Alternatively, rock phosphates (RP) can be used, but their low reactivity limits their use. Phosphate solubilizing microorganisms (PSM) can enhance RP dissolution and, thus, improve the RP agronomic effectiveness as fertilizer. Nonetheless, their effectiveness may be impaired by the soil P fixation capacity. An experiment was carried out to assess the in vitro effectiveness of the fungus Mortierella sp. to dissolve RP in an axenic culture medium and, thus, enhance the solution P concentration in the presence of aliquots of soils with contrasting P fixation capacity. The results showed that the fungus was capable of lowering the medium pH from 7.7 to 3.0 and, thus, dissolving the RP. The presence of soil aliquots in the medium controlled the effectiveness of the fungus to increase the concentration of the soluble P. In the presence of soils with a low or medium P sorption capacity, the concentration of the soluble P was high (63.8-146.6 mg L-1) in comparison with the inoculated (soilless) treatment (50.0 mg L-1) and the uninoculated control (0.7 mg L-1). By contrast, with very-high P fixing soil aliquots, the concentration of the soluble P was very low (3.6-33.1 mg L-1); in addition, in these soils, the fungus immobilized more P into its mycelia than in soils with a low or medium P fixation capacity. The capacity of a soil to fix P seems to be a good predictor for the effectiveness of this fungus to increase the soluble P concentration via RP dissolution.

Simple phosphorus saturation index to estimate risk of dissolved P in runoff from arable soils

Abstract. There is increasing evidence that phosphorus has been accumulating in the surface horizons of agricultural soils to the extent that some soils represent a potential diffuse source of pollution to surface waters. The relationships between equilibrium phosphorus concentration at zero sorption (EPC 0) of soil and a number of soil physicochemical variables were investigated in the surface layers of arable and grassland agricultural soils sampled from the Thame catchment, England. Soil EPC0 could be predicted from an equation including soil test (Olsen) P, soil phosphate sorption index (PSI) and organic matter content (OM) (R2=0.88; P<0.001) across a range of soil types and land use. The simple index Olsen P/PSI was found to be a good predictor of EPC0 (R2=0.77; P<0.001) and readily desorbable (0.02 m KCl extractable) P (R2=0.73; P<0.001) across a range of soil types under arable having soil organic matter contents of <10%.

Contents and weathering state of volcanic ashes and their effects on phosphate sorption in soils of the semiarid pampa of Argentina

Eolian parent materials of soils of the semiarid Argentinean Pampas show high volcanic ash contents. Weathering products of volcanic ashes can sorb anions in many soils. The objective of this study was to analyze the volcanic ash distribution in soils of the semiarid Pampas, its weathering state, and the influence of its weathering products on phosphate sorption. Sixteen soils, classified as Entic Hapludolls and Entic Haplus‐tolls, were studied at different landscape positions of five sites placed in a SW‐NE‐oriented climosequence within the semiarid Pampa. Results showed that volcanic ashes accumulated more in the subsoil of SW‐placed profiles and in the topsoil of NE‐placed profiles. Topsoil accumulated ashes of NE‐placed profiles were deposited by the eruption of Quizapu volcano in 1932. Subsoil accumulated ashes of SW‐placed profiles were deposited by older volcanic eruptions. Acid oxalate soluble Al (Alo), an index of the degree of volcanic ash weathering, was higher in the subsoil of profiles placed at the SW extremity of the sequence. The larger effect of ash age rather than climatic conditions on ash weathering rate was deduced. Allophane contents were low in all soils (<0.8%). Prevailing clay minerals were illite and very low crystallized intergrade illite‐smectites. Soils with the highest volcanic ash content also held the largest amounts of illite‐smectite intergrades. Alo contents explained 52% of sorbed phosphates, and only 36% of fixed P. By including the contents of exchangeable Ca2+ and CaCO3 into the model, 73% of sorbed P variations and 58% of fixed P variations were explained. No measurable effects of volcanic ashes on phosphate dynamics are expected to exist in soils placed to the north of the studied region, but in soils placed to the south, which have high contents of CaCO3 and exchangeable Ca2+, amorphous volcanic ash, weathering products can retain large amounts of phosphates.

Soil phosphate sorption and simulated runoff parameters as affected by fertilizer addition and soil properties

Abstract Changes in soil phosphate (P) sorption properties, soil P availability and two runoff‐related parameters, were determined on 32 Italian soils, following application of 100 mg P/kg soil. The ability of soil chemical and physical characteristics, in predicting the relative changes in soil P availability was investigated. Phosphorus Sorption Index (SI) gave the best estimate (r>0.76; P<0.001) of the potential for change in the studied P soil properties. Inclusion of SI into the fertilizer recomniendation process using soil P availability, may improve fertilizer‐use efficiency and reduce the potential for P loss in runoff

Predicting phosphate sorption in soils of mediterranean regions

Phosphate sorption curves give useful information about the management of the P fertility in soils. This study was conducted to examine how P sorption characteristics were influenced, and could be predicted from the properties of Mediterranean soils of Spain. The 114 soils studied differed widely in origin and properties and were grouped as calcareous (43) and noncalcareous (71). Citrate-bicarbonate-dithionite extractable Fe (Fed) and Al (Ald) and clay were the properties best correlated with the P sorbed and the P buffer capacity at an equilibrium concentration of 0.2 mg P l−1. This suggests that Fe oxides and silicate clays play a significant role in P sorption. Stepwise regression analysis showed, however, that clay was not a significant variable in the calcareous group, but active CaCO3 was. Prediction of the P sorption parameters was better for the noncalcareous than for the calcareous group. This reduced ability to predict P sorption in calcareous soils may be due to the inability of total or active CaCO3 to adequately measure the reactivity of carbonates towards P sorption. From 53 to 75% of the variation in P sorption parameters could be explained by regression equations including all or several of the following routinely-determined soil properties: clay, pH, Fed, and active CaCO3. These equations could, therefore, provide a simple and rapid estimation of P sorption in soils of Mediterranean regions.

Phosphorus sorption by acid soils: comparative study of some parameters

SummaryA comparative study of sorption maxima (simple and double Langmuir equations) and buffer capacity of acid soils was made in order to select the most useful P-sorption parameter. Data were obtained from 20 acid soils from Galicia (north-west Spain) and selection was made by linear and multiple regressions among sorption parameters, and between these and some soil characteristics related to phosphate sorption (clay and organicmatter content, pH in NaF, and 0·5 M-CuCl2-extracted Al).The phosphate buffer capacity, determined by the slope of the regression ‘sorbed-P v. logc’, was the best parameter to represent soil phosphate sorption behaviour. 0·5 M-CuCl2- extracted Al was the edaphic characteristic which best related to sorption properties.

Prediction of Phosphate Sorption in Soils from Regular Solid‐solution Theory

AbstractPotassium dihydrogen phosphate (KP) solutions or monocalcium phosphate (MCP) spot placed solids were reacted with eight acidic Missouri soils. After reacting the solid MCP with moist soil for 30 d, a 1‐g soil to 10‐g water suspension was made. Monocalcium phosphate soil suspensions and similar suspensions made with KP solutions were shaken for 16 d. The pH, Eh, electrical conductivity, Al, Ca, Fe, and P contents of the solutions were measured. It was postulated that P sorption sites were not independent of each other, but were altered by P sorbed at adjacent sites and that P sorption could be considered to behave as predicted for a regular solid‐solution. Observed values of P sorbed (PS) and P in solution were fitted to the following equation derived for a regular solid‐solution system: In P = A + B(PS) + C(PS)2. The data for the eight soils fit this equation with regression coefficients (r2) for KP which varied from 0.97 to 0.99 and for MCP from 0.88 to 0.97. The data were fitted to the linear form of the equation; In P = In Pmax + B′(1‐PS/PSmax)2, and no appreciable curvature was observed. The addition of 200 to 800 mg P/kg to soil as KP resulted in higher concentrations of P in solution than when equal amounts of MCP were added. This effect was attributed to MCP dissolving additional reactants capable of precipitating P. When 100 mg P/kg or less was added the concentrations of soluble P from KP and MCP were similar, except in the Barco soil where the addition of MCP resulted in a higher concentration of soluble P than the addition KP.