Phosphorus Sorption Research Articles

Multi-decadal impacts of effluent loading on phosphorus sorption capacity in a restored wetland

Natural wetlands are widely used and cost-effective systems for the passive remediation of phosphorus (P)-rich surface waters from various effluent sources. Yet the long-term biogeochemical impacts of effluent loading on wetland P retention capacity is unclear. Here, we had a unique opportunity to document the spatio-temporal evolution of sediment P sorption over a ∼25-year period of constant municipal and industrial effluent loading, as part of a wetland restoration and wastewater treatment strategy in one of the largest restored wetlands in Canada. Sediment P sorption experiments across Frank Lake's three basins revealed a wide spatial variation in sorption capacity, closely linked to sediment geochemistry gradients (Ca, Fe, and Mn). Relative to a similar study ∼25 years prior, P sorption capacity has become exhausted near the effluent inlet, but remarkably, remains elevated throughout the rest of the wetland. Compared to other prairie wetlands and global aquatic ecosystems, Frank Lake has a greater capacity overall to retain P through sediment sorption. Given the paucity of long-term (multi-decade) data on wetland response to effluent loading, we provide key insights into the dynamics of wetland P cycling in human-dominated watersheds.

Integrating soil phosphorus sorption capacity with agronomic indices to improve sustainable P use in agriculture

PurposePhosphorus (P) sorption processes in soils can influence P plant-availability and influence ‘build-up’ and ‘draw-down’ P cycles. Current fertiliser recommendations do not take these processes into account. This study aimed to integrate soil P sorption behaviour and P agronomic-indices to strengthen P management recommendations.MethodsMineral soil covering 35,716-km2 of Ireland was characterised by P status (Morgan’s P and Mehlich-3 P), and Langmuir sorption parameters of P sorption maximum capacity (Smax, mg·kg−1) and binding energy (k, L·mg−1).ResultsSegmented regression between Smax and M3-Al (R2 = 0.49) identified a significant change-point at Smax = 450.03 mg·kg−1, at which soils can be placed into ‘low’ (SLM3-Al) and ‘high’ (SHM3-Al) P sorbing classes. Sorption parameters in SLM3-Al did not change with soil P status; however, in high P sorbing soils, sorption parameters significantly correlated with P status. High sorbing soils that are P-deficient (Index 1 and 2) will ‘fix’ P and take longer to build-up plant available P to a value for agronomic production (Index 3). Low P sorbing soils at high P status (Index 4) will decline to Index 3 at faster rates than high P sorbing soils. These soils (SLM3-Al) are at higher risk of soluble P losses to water because of lower binding energies.ConclusionsEfficient P fertiliser use can be more effective if soils are delineated into ‘low’ and ‘high’ sorbing soils coupled with soil P status. By integrating P sorption capacities with agronomic soil P indices, fertiliser advice and water quality measures can be targeted and more effective.

Phosphorus Adsorption as Affected by Concretionary Nodules of Oxic Rhodustalf in Southern Guinea Savannah Agroecological Zone of Nigeria

Hard, rounded masses of mineral matter, known as concretionary nodules, can be found in soil or sedimentary rock. These nodules are typically made up of minerals like iron oxides, hydroxides, and carbonates that have been deposited in groundwater. Their sizes can range from small pebbles to large boulders, and they often differ in composition or hardness compared to the surrounding rock or soil. Nodules act as a highly effective storage space for extra P, leading to a significant increase in overall P requirements. Phosphorus, although an essential element for all living organisms, including plants and animals, is scarce. Despite its importance, only a small fraction of the total phosphorus available can be readily absorbed by plants. Given the worldwide demand for phosphorus in food production, it is crucial to devise techniques for extracting it from different sources. However, there has been limited research on the understanding of phosphorus availability and adsorption mechanisms in these areas. Therefore, the study focused on exploring the impact of concretionary nodules on phosphorus sorption and the characteristics of low-activity clay soil in the Guinea savannah of Nigeria. Soil samples collected from the study area were used to investigate the soil’s ability to absorb phosphorus at depths ranging from 0 to 30-60-90-120-150 cm in different soil and concretion locations. Various soil and concretion types demonstrated distinct capacities for phosphorus adsorption, as indicated by the adsorption isotherm. The maximum monolayer adsorption capacities (Qmax values) were 161.0, 154.5, 149.6, 141.7, 139.8, and 139.3 mg/g for OBC, OBS, OC, OIS, OS, and OIC, respectively. At equilibrium with a 50-ppm solution, the pseudo-second-order rate constants for P sorption were 1.180 x 10<sup>–4</sup>, 9.740 x 10<sup>–5</sup>, 1.120 x 10<sup>–4</sup>, 1.140 x 10<sup>–4</sup>, 1.000 x 10<sup>–4</sup>, and 8.010 x 10<sup>–5</sup> g mg<sup>–1</sup> min<sup>–1</sup> for OIS, OIC, OBS, OBC, OS, and OC, in that order. In the 300-ppm equilibrium solution, the OIS, OIC, OBS, OBC, OS, and OC pseudo-second-order rate constants were 1.250 x 10<sup>–4</sup>, 1.130 x 10<sup>–4</sup>, 9.550 x 10<sup>–5</sup>, 1.040 x 10<sup>–4</sup>, 2.750 x 10<sup>–4</sup>, and 1.420 x 10<sup>–4</sup> g mg<sup>–1</sup> min<sup>–1</sup>, respectively. At the 500-ppm equilibrium, the pseudo-second-order rate constants for OIS, OIC, OBS, OBC, OS, and OC were 1.240 x 10<sup>–4</sup>, 1.090 x 10<sup>–4</sup>, 1.020 x 10<sup>–5</sup>, 1.100 x 10<sup>–4</sup>, 2.730 x 10<sup>–4</sup>, and 1.180 x 10<sup>–4</sup> g mg<sup>–1</sup> min<sup>–1</sup>, respectively. Consequently, the soil adsorption capacity increased with higher pseudo-second-order rate constants.

Comparing the potential of benchtop and handheld mid-infrared spectrometers for predicting soil phosphorus (P) sorption capacity and evaluating the influence of sample preparation

Traditional soil phosphorus (P) sorption capacity is examined from a Langmuir isotherm batch technique, which is time-consuming, labour intensive and generates chemical waste. In this work, we provide an efficient and convenient technique with MIR spectroscopy to predict the Langmuir parameter of soil P sorption maximum capacity (Smax, mg·kg−1).Four spectral libraries from benchtop (Bruker) and handheld (Agilent) MIR spectrometers were built with samples in two particle size ranges, <0.100 mm (ball-milled) and <2 mm. respectively. Using an archive of samples with a database of sorption parameters, soils were classified into ‘low’ and ‘high’ sorption capacities. Chemometric regression models of partial least squares (PLS), Cubist, support vector machine (SVM) regression and random forest (RF) were evaluated for Smax prediction. Bruker spectral libraries with both soil particle sizes yielded ‘excellent models’, with SVM predicting Smax values with high accuracy (RPIQV = 4.50 and 4.25 for the spectral libraries of the ball-milled and <2 mm samples, respectively). In comparison, the Agilent handheld spectral libraries contained more noise and less resolution. For Agilent MIR spectroscopy, more homogeneous samples after ball milling resulted in a higher accurate Smax prediction. For Agilent libraries of ball-milled samples, an ‘approximate quantitative model’ (RPIQV = 2.74) was obtained from the raw spectra using the Cubist algorithm. However, for Agilent spectroscopy of <2 mm samples, the best performing Cubist algorithm can only achieve a ‘fair model’ (RPIQV=2.23) with the potential to discriminate between ‘low’ and ‘high’ Smax values.The results suggest that the benchtop spectrometer can predict the Langmuir Smax value with high accuracy without the need to ball mill samples. However, the handheld spectrometer can only make approximate quantitative predictions of Smax for ball-milled samples. For <2 mm samples, Agilent can only be used to classify ‘low’ and ‘high’ sorption capacity soils.

Edaphic Factors Modulating Phosphorus Availability in Lowland Rice Systems, Nigeria

ABSTRACT The low rice production level in Africa is attributed to poor soil fertility despite the potential for rice cultivation in the inland valleys. This study was conducted to evaluate soil characteristics in some lowlands that have been continuously and intensively used for rice production for over two decades in southwestern Nigeria. Soil physical, chemical, and mineralogical properties, as well as phosphorus sorption characteristics, were assessed in soil samples collected from diagnostic horizons of profiles in six benchmark soils. The results show kaolinite, quartz, potassium(K)-feldspars, and mixed-layered smectite as the predominant minerals. The iron oxide fractions indicate that the soils are at varying degrees of development where the soils at the advanced stage of development are predominantly rich in kaolinite and quartz with a high concentration of total pedogenic iron oxide and generally low in soil fertility. Soil phosphorus buffering capacity is low and varies inversely with pH, confirming the deficiency of phosphorus at low pH. Short-range-order (SRO) iron (Fe) oxides show a strong affinity for phosphorus and this is stronger at lower soil horizons and mediated by some redoxomorphic reactions. The SRO iron oxide concentration has more influence on phosphorus retention in soils rather than the absolute concentration of iron oxides. The study concludes that SRO Fe oxides and soil pH are the major edaphic factors playing a prominent role in phosphorus retention and availability in the wetland soils rather than the clay minerals.

Influence of corn stalk and corn stalk biochar application on the strategy of phosphorus sorption and release in brown earth

AbstractThe characteristics of soil phosphorus (P) fixation and release have a critical impact on the availability of P and the risk of environmental loss. Investigation of the effects of corn stalk and corn stalk biochar on the P adsorption–desorption characteristics of brown earth can provide a theoretical basis for the rational return of crop stalk to the field and improving the availability of soil P. The Langmuir adsorption isotherm equation provided a better fit than the Freundlich equation for the curve of soil P adsorption and equilibrium solution P concentration. Biochar application increased the maximum adsorption capacity (MAC) and maximum buffer capacity (MBC) of the soil for P by 8.5% and 17.2%, respectively. Corn stalk and its biochar reduced the P adsorption saturation (DPS) by 41.8% and 31.9%, respectively, but increased the amount of readily desorbable P (RDP) by 39.7% and 154.4%, respectively. The application of corn stalk and its biochar improved the soil P desorption rate at substrate P concentrations of less than 5 mg L−1, whereas significant reductions in the soil P desorption rate were observed between 5 mg L−1 and 30 mg L−1, and no significant effects were observed at P concentrations over 40 mg L−1. In addition, the total P and Olsen‐P contents of the soil were significantly associated with the P adsorption–desorption process (p &lt; .05). Therefore, corn stalk and corn stalk biochar can enhance the capacity of soil for P adsorption, with a stronger effect observed for biochar than for corn stalk, and the rate of P desorption from treated soil is dependent on P concentration in the soil solution.

Soil Properties Related to Phosphorus Sorption and Prediction of Maximum Phosphorus Adsorption Capacity of Soils from Southern Brazil

Soil Properties Related to Phosphorus Sorption and Prediction of Maximum Phosphorus Adsorption Capacity of Soils from Southern Brazil

Phosphorus sorption–desorption changes phosphorus fraction dynamic in a desert revegetation chronosequence

AbstractUnderstanding the characteristics of soil phosphorus (P) sorption and desorption is essential for comprehending P biogeochemical cycling and effectively managing ecosystems in a desert revegetation chronosequence. The present study utilized the Freundlich model and enzymatic activity to characterize the features of P sorption–desorption, and microbial activity, which aims to elucidate the effect of P kinetics and microbial activity on P fractions in the soils of a desert revegetation chronosequence, consisting of 11, 31, 40, 57, and 65 years old revegetated deserts. The findings revealed that the 31 years old soil showed the highest alkaline phosphomonoesterase and phosphodiesterase activities, and the 40 years old displayed the highest inorganic pyrophosphatase activity. In revegetated desert soils, microbial activity changed P sorption–desorption kinetics by decreased or increased the parameters including sorption/desorption energy site, P sorption/desorption ability, and the maximum buffering capacity of P sorption/desorption. And in microbial activity soils of 31–40 years old, P desorption significantly decreased T‐P and A‐P concentrations (p &lt; 0.05). P sorption process and enzyme activity explained 35.10% and 22.20% of P fraction variation, respectively; and P desorption process and enzyme activity explained 48.3% and 22.3% of P fraction variation, respectively. These findings provide valuable insights into the contribution of P kinetics coupled with microbial activity in desert ecosystems, aiding in the effective management of these fragile ecosystems.

Sorption-Desorption of Phosphorus on Manure- and Plant-Derived Biochars at Different Pyrolysis Temperatures

Sustainable phosphorus (P) management is essential to preventing mineral fertilizer losses, reducing water pollution, and addressing eutrophication issues. Phosphorus sorption and mobility are strongly influenced by the properties of biochar, which are determined by pyrolysis temperature and type of feedstock. This understanding is crucial for optimizing biochar application for soil nutrient management. Therefore, a batch sorption-desorption experiment was conducted to examine P sorption-desorption in plant-based (parthenium, corn cobs) and manure-based (farmyard manure, poultry manure) biochars prepared at both 400 °C and 600 °C. Manure-based biochars demonstrated higher P sorption at 400 °C, with less sorption at 600 °C, while plant-based counterparts exhibited lower sorption capacities. Phosphorus desorption, on the other hand, increased at 600 °C, particularly in manure-based biochars. The scanning electron microscopy (SEM) and Fourier-transform infrared spectra (FTIR) analysis suggested that a lower pyrolysis temperature (400 °C) enhances P sorption due to higher specific surface area and different functional groups. Additionally, the manure-based biochars, which were enriched with calcium (Ca) and magnesium (Mg), contributed to increased P sorption. In summary, P sorption is enhanced by a lower carbonization (400 °C) temperature. Although manure-based biochars excel in retaining P, their effectiveness is limited to shorter durations. In contrast, plant-based biochars showcase a prolonged capacity for P retention.

Effects of redox on the phosphorus removal ability of iron-rich phosphorus sorption materials

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.

Effects of forest regeneration types on phosphorus fractions of soil aggregates in subtropical forest.

Soil aggregates are important for the storage and availability of phosphorus in the soil. However, how forest regeneration types affect phosphorus fractions of soil aggregates remains unclear. In this study, we examined the composition of aggregate particle size, phosphorus fractions, phosphorus sorption capacity index (PSOR), legacy phosphorus index (PLGC) and degree of phosphorus saturation by Mehlich 3 (DPSM3) in bulk soils and soil aggregates of Castanopsis carlesii secondary forest (slight disturbance), C. carlesii human-assisted regeneration forest (moderate disturbance), and Cunninghamia lanceolata plantation (severe disturbance), aiming to explore the impact of forest regeneration types on phosphorus availability and supply potential of bulk soils and soil aggregates. The results showed that forest regeneration types significantly influenced the composition of soil aggregates. The proportion of coarse macroaggregates (>2 mm) in the soil of C. carlesii secondary forest and human-assisted regeneration forest was significantly higher than that in the C. lanceolata plantation, while the proportion of silt and clay fraction (<0.053 mm) showed an opposite trend. The composition of soil aggregates significantly affected the contents of different phosphorus fractions. The contents of soil labile phosphorus fractions (PSOL and PM3) decreased as aggregate particle size decreased. The contents of soil total phosphorus (TP), total organic phosphorus (Po), mode-rately labile phosphorus fractions (PiOH and PoOH), and occluded phosphorus (POCL), as well as PSOR and PLGC, exhibited a trend of decreasing at the beginning and then increasing as particle size decreased. The contents of TP, Po, and PiOH in coarse and silt macroaggregates was significantly higher than that in fine macroaggregates (0.25-2 mm) and microaggregates (0.053-0.25 mm). Forest regeneration types significantly influenced the contents of phosphorus fractions of bulk soils and soil aggregates. The contents of TP, Po, PSOL, and PM3 in the soil of C. carlesii secondary forests was significantly higher than that in C. carlesii human-assisted regeneration forest and C. lanceolata plantation. The contents of PSOL and PM3 in different-sized aggregates of C. carlesii secondary forests were significantly higher than that in the C. lanceolata plantation. Forest regeneration types significantly influenced the composition and supply potential of phosphorus fractions in soil aggregates. The proportions of PSOL, and PM3 to TP in different-sized soil aggregates were significantly lower in C. carlesii human-assisted regeneration forest compared with C. carlesii secondary forest. PSOR and DPSM3 in different-sized soil aggregates were significantly lower in C. lanceolata plantation than that in C. carlesii secondary forest. Overall, our results indicated that natural regeneration is more favorable for maintaining soil phosphorus availability, and that forest regeneration affects soil phosphorus availa-bility and its supply potential by altering the composition of soil aggregates.

Enhancement of Phosphorus Sorption onto Peanut shell by Means of Aluminum and Iron Oxide Coatings

Phosphorus serves as a crucial nutrient for the organisms. Still, the discharge of high levels of phosphate concentrations into limited aquatic environments leads to the phenomenon known as eutrophication, which subsequently leads to the degradation of the overall water quality. In this study the capacity of the peanut shell, Al-coated and Fe-coated is determined in relating by adding 10, 20, and 30, 40 mg P L-1 as (KH2PO4) to 1.0 g of each sample and shaking for 2, 6, 12, and 24 h and at pH ranged between 4.6, 5.2, 6.3 and 7.8. At the end of each period, the suspension was filtered and analyzed which presents the concentration of equilibrium P. The maximum P adsorption of 28.9±0.07 and 50.6±0.49% was recorded for 24 h of incubation and at pH (4.6) with an Al-coated peanut shell respectively. The findings of this study demonstrated that the adsorption of phosphorus (P) increased as the duration of incubation increased. At the same time, it decreased with a decrease in the pH of the solution. Furthermore, the outcomes indicated that the Freundlich model provided the best fit for the data, based on higher R2 values ranging from 0.9867 to 0.9938, in comparison to the range of 0.9659 to 0.9904 observed for the Longmuir model. These results suggested that peanut shells coated with Al can be used to remove high amounts of P in the solution. Also, the removal resulted from the physical adsorption of P rather than a chemical reaction.

Fijación de fosforo en sedimientos de fondo de los Ríos Paraná, Paraguay y Bermejo

Phosphorus sorption'from Solutions containing 0-5 mgP/l was studied in bottom sediments from Paraná, Paraguay and Bermejo rivers. Sorptidh frtted a Langmuir isotherm with phosphate sorption capacities of 96, 87 and 52 MgP/g (dry weight) sediment. Hieltjesand Lijklema (1980) phosphorus fractionation showed that the iron bound phosphate is the mainfraction in the Paraná and Paraguay sediments while the calcium bound phosphorus is the main fraction in the Bermejo sediments. Caleiuhi content was high (32 mg/g) in the Bermejo sediments and low (5.5 and 5;3 mg/g) in the Paraná and Paraguay sediments, respectively, The organic matter composition is also dlfferent in the three rivers being the Paraná and the l^íraguay ríchér in huihic ^ibstánces. Low phosphorus content and sorption capacity in the three sediments are thought to be related with a granulometry dominated by the coarse fractions. Clay size partióles only accounted for 13-23 % of the total sediment weight.

The Effects of Dissolved Organic Matter Derived from Agricultural Waste Materials on Phosphorus Sorption in Sandy Soils

The effect of organic matter (OM) on soil phosphorus (P) sorption is controversial, as there is still no clear answer whether organic matter inhibits or increases P sorption. Despite the great need for renewable sources of available P and OM in agricultural soils, little is known about the interaction between P and dissolved organic matter (DOM) in natural soil systems. The aim of this research was to uncover if and how soil saturation with DOM derived from different types of abundant agricultural wastes (cattle manure, horse manure, biogas digestate, compost) affects the phosphate sorption. We examined the P sorption process in control and DOM-saturated sandy soils. The results indicated that OM introduced with agricultural waste did not always reduce P sorption, but certainly had an effect on impairing P fixation, and thus, may result in potentially greater P mobility in the soil, including P availability. Among these waste materials, DOM from horse manure had the most positive effect on P mobilization; thus, horse manure—if available—is recommended for spreading on soils with low P mobility.

Microplastic-Assisted Removal of Phosphorus and Ammonium Using Date Palm Waste Derived Biochar.

Microplastics (MPs) are emerging environmental pollutants worldwide, posing potential health risks. Moreover, MPs may act as vectors for other contaminants and affect their fate, transport, and deposition in the environment. Therefore, efficient and economical techniques are needed for the removal of contemporary MPs and contaminants from the environment. The present research study investigated the sorption of phosphorus (P) and ammonium (NH4+) onto date palm waste-derived biochar (BC) from an aqueous solution in the presence of polyamide (PA) and polyethylene (PE) MPs. The BC was prepared at 600 °C, characterized for physio-chemical properties, and applied for P and NH4+ removal via isotherm and kinetic sorption trials. The results of the sorption trials demonstrated the highest removal of NH4+ and P was obtained at neutral pH 7. The highest P sorption (93.23 mg g-1) by BC was recorded in the presence of PA, while the highest NH4+ sorption (103.76 mg g-1) was found with co-occurring PE in an aqueous solution. Sorption isotherm and kinetics models revealed that P and NH4+ removal by MP-amended BC followed chemisorption, electrostatic interaction, precipitation, diffusion, and ion exchange mechanisms. Overall, co-existing PA enhanced the removal of P and NH4+ by 66% and 7.7%, respectively, while co-existing PE increased the removal of P and NH4+ by 55% and 30%, respectively, through the tested BC. Our findings suggested that converting date palm waste into BC could be used as a competent and economical approach to removing P and NH4+ from contaminated water. Furthermore, microplastics such as PE and PA could assist in the removal of P and NH4+ from contaminated water using BC.

Influence of lime and organics on phosphorus sorption–desorption kinetics in red-lateritic soils of West Bengal

Influence of lime and organics on phosphorus sorption–desorption kinetics in red-lateritic soils of West Bengal

Converting natural forests to tea plantations reduced soil phosphorus sorption capacity in subtropical China

AbstractConverting natural forests to agricultural lands has been widespread globally due to increasing population and the demand for food. Phosphorus (P) is often applied to agricultural lands in excessive amounts which can saturate the natural P sorption capacity of the soil, leading to P leaching and subsequent off‐site water eutrophication. We studied the effect of land‐use conversion from natural forests to tea plantations on total soil P, P fractions, and P sorption capacity in subtropical China. Compared to natural forests, total soil P concentrations increased significantly in both 0–20 and 20–40 cm depths in tea plantations, indicative of the accumulation of P fertilizer. The increases in total soil P were primarily found in NaOH‐extractable inorganic P and residual P fractions in both depths, suggesting that P fertilizer was sorbed and occluded into more stable forms due to the high abundance of sorbents (i.e., iron [Fe], aluminum [Al] minerals, and clay). Across all soil samples, oxalate‐extractable Fe was the best predictor of soil maximum P sorption capacity (r = 0.94, p &lt; 0.001). Surprisingly, the conversion from natural forests to tea plantations decreased both oxalate‐extractable Fe concentration and soil maximum P sorption capacity, hereby increasing the degree of P saturation in soils. Depletion of P sorbents (i.e., soil amorphous Fe) is likely a consequence of Fe removal through tea production and soil erosion, indicating soil degradation. Plantation soils have also shown other signs of degradation including the loss of nutrients (e.g., total soil nitrogen and oxalate‐extractable calcium) and soil organic matter. Our results demonstrate that the conversion of natural forests to tea plantations reduced the ability of the soil to sorb P by both saturating the natural P sorption capacity and depleting P sorbents. Soil degradation resulting from land‐use conversion has increased the environmental risk of P leaching loss, emphasizing the need for improved P fertilization management.

Phosphorus Sorption by Purple Soils in Relation to Their Properties: Investigation, Characterization, and Explanation

Improved soil phosphorus (P) management can be achieved through an understanding of regional soil–P interactions and their relation to soil properties. To this end, soil samples from different use types (paddy soils, dry farmland soils, forest soils, and urban green land soils) were collected from 10 sites across the west to the east of Sichuan Basin, China. These samples were analyzed to determine their P sorption properties and physical and chemical compositions. P sorption was described using a modified Freundlich equation. The results demonstrated a gradient in P sorption within the basin, characterized by higher values in urban areas and a west-to-east decrease trend, along with the null-point values of soil sorption–desorption equilibrium. This variation was linked to the extensive use of P fertilizer, which altered soil particle surface conditions and significantly reduced both the quantity and rate of subsequent fertilizer sorption. Furthermore, P sorption was found to be correlated with the soil clay fraction, amorphous aluminum oxides, and soil organic matter contents. Urban expansion and accelerated erosion of productive agricultural land increase mean soil particle size and may decrease soil P holding and retention capacity. As preliminary deterioration in soil properties was found, conservative soil management is needed to address the potential threats of soil degradation in the central Sichuan Basin.

Phosphorus Sorption by Saline Soils of Western Transbaikalia

The sorption of phosphorus by salt marshes of the dry-steppe zone of the Republic of Buryatia from an aqueous solution of KN2PO4 in the concentration range from 0.25 to 5.0 mM/L (mmol/L) was studied under static conditions. The interaction time is 24 hours with a soil: solution ratio of 1 : 10. The amount of sorbed phosphorus was calculated from the difference in its content in the initial solutions and in the filtrates of soil suspensions. Based on experimental data, phosphorus adsorption isotherms were constructed by soil and sorption parameters were calculated using the Langmuir and Freundlich equations. Typical and quasi-clay Solonchaks have relatively high sorption properties with respect to phosphorus. The value of the maximum adsorption capacity (Amax) in the humus horizons of these soils varied in the range of 23.04–42.74 mM P/kg, in the underlying horizons 16.26–30.39 mM P/kg. In general, all soils, with the exception of the sorov Solonchaks, had an Amax value in the range of 17.70–42.74 mM P/kg. A low sorption value of phosphorus was found in the Solonchaks of sorovy. The Langmuir adsorption constant (KL) varied in the range of 0.3–14.0 l/mmol. Solonchaks dark and typical most strongly bind phosphorus. The Freundlich coefficient (KF) in the studied soils varied in the humus horizon from 5.34 to 63.43 mM P/kg, in mineral from 1.74 to 22.68 mM P/kg. The distribution coefficient (Kd) ranged from 1.95–145.04 l/kg with high values for quasi-clay Solonchaks and low for sorov Solonchaks. The correlation between Kd and Amax was estimated as average (r = 0.51), Kd and KL – high (r = 0.84, p ≤ 0.05). The studied soils according to the values of SPR (the amount of phosphorus that must be sorbed by the soil to maintain a concentration of P = 0.2 mg/kg (0.0065 mM/l) in soil solution) from (0.0723 to 3.4836 mM/kg) refer to weakly absorbing phosphorus. According to the ability to sorb phosphorus, soils form the following decreasing series: quasi-glay solonchaks typical solonchaks dark solonchaks glay solonchaks alluvial light humus saline sorov solonchaks.

Phosphorus Sorption by Saline Soils of Western Transbaikalia

Phosphorus Sorption by Saline Soils of Western Transbaikalia