Soil sorption–desorption of phosphorus from piggery effluent compared with inorganic sources

The leaching of phosphorus (P) within soils can be a limiting consideration for the sustainable operation of intensive livestock enterprises. Sorption curves are widely used to assist estimation of P retention, though the effect of effluent constituents on their accuracy is not well understood. We conducted a series of P‐sorption–desorption batch experiments with an Oxic Haplustalf (soil 1), Haplusterts (soils 2 and 3), and a Natrustalf (soil 4). Phosphorus sources included effluent, orthophosphate‐P in a matrix replicating the effluent's salt constituents (the reference solution), and an orthophosphate‐P solution. Treated soils were incubated for up to 193 days before sequential desorption extraction. Effluent constituents, probably the organic or particulate components, temporarily increased the vulnerability of sorbed‐P to desorption. The increase in vulnerability was removed by 2–113 days of incubation (25°C). Despite vigorous extraction for 20 consecutive days, some P sorbed as part of the treatments of soils 1 and 2 was not desorbed. The increased vulnerability due to effluent constituents lasted a maximum of about one cropping season and, for all other treatments, adsorption curves overestimated vulnerability to desorption. Therefore, adsorption curves provide a conservative estimate of vulnerability to desorption where effluent is used in continued crop production in these soils.     

The effects of freeze‐and‐thaw cycles on phosphorus availability in highland soils in Turkey

Ongoing global warming may result in colder soil and thawing cycles and will increase the frequency of soil freezing‐and‐thawing‐treated cycles (FTCs) during winter in the cool‐temperate and high‐latitude regions. The purpose of this study was to determine the effects of repeated freeze–thaw cycles on the solubility and adsorption of P in lab and field experiments on Pellustert, Argiustoll, Haplustept, Fluvaquent, and Calciorthid soils, the major soil groups in E Turkey. The results demonstrated that, depending on the soil type, the freeze–thaw cycle could increase the adsorption and desorption of P within a certain temperature range. Repeated freezing and thawing decreased equilibrium P concentration (EPC) and increased P adsorption. EPC and P adsorption were strongly correlated with the number of FTCs. The highest P adsorption and the lowest P desorption was found in Pellustert followed by Argiustoll, Calciorthid, Haplustept, Fluvaquent when refrozen at –10°C for 15 d, then thawed at +2.5°C for 18 h, and 9 times FTC. However, in the field study, the adsorption value was lower than the value obtained from the laboratory condition. It appears that increasing the frequency of freeze–thaw processes depending on increase in temperature that leads to decreased plant‐available soil P pools, thus requires more P fertilizer in soil solution to supply adequate P during the plant‐growth period.     

Adsorption and Desorption of Copper in Pasture Soils

Abstract

Copper (Cu) is bound strongly to organic matter, oxides of iron (Fe) and manganese (Mn), and clay minerals in soils. To investigate the relative contribution of different soil components in the sorption of Cu, sorption was measured after the removal of various other soil components; organic matter and aluminum (Al) and Fe oxides are important in Cu adsorption. Both adsorption and desorption of Cu at various pH values were also measured by using diverse pasture soils. The differences in the sorption of Cu between the soils are attributed to the differences in the chemical characteristics of the soils. Copper sorption, as measured by the Freundlich equation sorption constants [potassium (K) and nitrogen (N)], was strongly correlated with soil properties, such as silt content, organic carbon, and soil pH. The relative importance of organic matter and oxides on Cu adsorption decreased and increased, respectively, with increasing solution Cu concentrations. In all soils, Cu sorption increased with increasing pH, but the solution Cu concentration decreased with increasing soil pH. The cumulative amounts of native and added soil Cu desorbed from two contrasting soils (Manawatu and Ngamoka) during desorption periods showed that the differences in the desorbability of Cu were a result of differences in the physico‐chemical properties of the soil matrix. This finding suggests that soil organic matter complexes of Cu added through fertilizer, resulted in decreased desorption. The proportions of added Cu desorbed during 10 desorption periods were low, ranging from 2.5% in the 24‐h to 6% in the 2‐h desorption periods. The desorption of Cu decreased with increasing soil pH. The irreversible retention of Cu might be the result of complex formation with Cu at high pH.     

Effects of temperature on phosphate sorption isotherms and phosphate desorption

Abstract

Phosphorus sorption isotherms were constructed for two Idaho soils with widely different chemical properties. The soils were equilibrated with various amounts of Ca(H₂PO₄)₂ in 0.01 M CaCl₂ for 1, 3, 7, and 11 days at temperatures of 5°C and 20°C. The two soils which had been equilibrated previously for 11 days at 20°C with various amounts of Ca(H₂PO₄)₂ in 0.01 M CaCl₂ were desorbed at 5°C and 20°C.

The rates of sorption and desorption were decreased as the equilibration temperatures were lowered. The effect of temperature on these processes was detected during the first day of equilibration. Less P was found in the equilibrating solution at the lower temperature. The two soils varied widely in sorption and desorption properties.     

Adsorption-desorption of atrazine on four soils of Hyderabad

The adsorption-desorption equilibrium of atrazine (2-chloro, 4-ethylamino, 6-isopropyl amino-1, 3, 5 triazine) was studied by the batch equilibration method at 27 ± 1 °C on four soils of Hyderabad. Adsorption isotherms conformed to the Freundlich equation (A = KC^1/n ). K increased in the same order as the organic C content of the soils. Desorption studies were conducted by repeated replacement of 5 mL of the supernatant equilibrium solutions after adsorption, with 0.01 M CaCl₂. Desorption isotherms showed considerable hysteresis which was more prominent when the desorption was carried out with higher adsorbed concentration of atrazine. Desorption from the lowest level of adsorbed atrazine (3 to 5 μg g^?1 soil) was close to the adsorption isotherm. The cumulative desorption after four desorption steps covering five days was significantly different at the 1% level, for different initial adsorbed concentrations of atrazine. Desorption was significantly higher at the lowest adsorbed level of atrazine. The soils differed significantly at 6% level for desorption and the amount desorbed decreased in the inverse order of organic C. Desorption isotherms also conformed to Freundlich equation but K andn values were both higher than that for adsorption and increased with increase in initially adsorbed concentration of atrazine. Desorption thus confirmed the irreversible nature of the adsorption of atrazine on these soils. The quantitative factors and reasons for desorption are discussed.     

Effects of drying on the ion exchange capacity and cation adsorption properties of some New Zealand soils

Abstract

The effect of drying on the cation (CEC) and anion (AEC) exchange capacity, and on potassium (K) and magnesium (Mg) adsorption by three New Zealand soils was investigated. Air‐drying resulted in no significant changes in these properties compared with the field‐moist samples. Oven‐drying at 105°C significantly decreased the CEC and increased the AEC of most soils compared with air‐dried samples. The decrease in CEC was related to increased solubility of organic matter and a decrease in surface area on which charge could be developed. The increase in AEC was attributed to a decrease in soil pH.

Potassium and Mg adsorption by two soils decreased following oven‐drying. This was consistent with the effect of drying on CEC. For the remaining soil, K adsorption increased following oven‐drying. This was attributed to K fixation.     

Manganese retention by selected calcareous soils as related to soil properties

Abstract

Calcareous soils often need supplemental manganese (Mn) to support optimum plant growth, but some reports show that the apparent recovery of applied Mn is very low in such soils, i.e., nearly all of the applied Mn is retained in the soil. This experiment was conducted to find the relationship between the retained Mn and selected properties of calcareous soils. Eleven surface (0–20 cm) soil samples with pH ranging from 7.7 to 8.1 and calcium carbonate equivalent (CCE) ranging from 20 to 50% were used in the Mn adsorption study. Two‐gram subsamples of each soil were equilibrated with 20 mL of 0.01M CaCl₂ solutions initially containing 10 to 200 mg Mn L^‐1. The Mn that disappeared from solution (after 6 h shaking at 25°C) was considered as adsorbed (retained) Mn. The adsorption data showed a highly significant fit to Freundlich and also to the two‐surface Langmuir adsorption isotherms. The coefficients of both isotherms showed significant positive correlations with cation exchange capacity (CEC), organic matter (OM), and CCE of the soils indicating that OM and calcium carbonate are the sites of Mn retention in calcareous soils. Comparison of the adsorption data of this experiment with those of plant Mn uptake of the same soils (published earlier) shows that as the Langmuir second surface adsorption maxima (maximum retention capacity) of the soils increase the plant Mn concentration and uptake decrease.     

Time‐dependent zinc desorption in soils

Abstract

Time dependent zinc (Zn) desorption in eight benchmark soils of India was studied in relation to various pH values and ionic strengths. Soil samples were equilibrated in solutions containing 10 μg Zn g^‐1 soil at pH 5.5,6.5, and 7.5 for 48 h at 25±2°C, and adsorbed Zn extracted with calcium chloride (CaCl₂) for various periods of time. Desorption of Zn decreased with increasing pH, and the desorption rate decreased abruptly at pH 7.5. In contrast, an increase in the equilibration period and ionic strength of the background electrolyte increased Zn desorption. Four rival kinetic models were fitted and evaluated for their suitability for describing the Zn desorption process. Reaction rate constant (ß) calculated from the Elovich model for the different soils ranged from 9.99 to 25 (mg Zn kg^‐1)^‐1. The different kinetic models tested indicated that Zn desorption in soils was a diffusion controlled process. The desorption was rapid in the first 4 h, followed by slower phase in the rest of the time at all the pH values indicating a biphasic desorption, characteristic of a diffusion controlled process. The ß value for the Elovich equation showed a strong association with soil clay content and cation exchange capacity (CEC). Further, the best prediction of Zn desorption reaction rate constant could be made using multiple‐regression equation with soil clay content and CEC as variables.     

Phosphorus adsorption and desorption in undisturbed samples from subtropical soils under conventional tillage or no‐tillage

The dynamics of P in soil is greatly influenced by the adsorption of phosphate onto Fe‐oxides. Access of phosphate to the surface of these minerals depends on the degree of soil aggregation, which in turn is influenced by soil management system. The primary purpose of this work was to investigate P adsorption and desorption in undisturbed and disturbed soil samples from an Ultisol (Rhodic Paleudult) and an Oxisol (Humic Hapludox) under conventional tillage (CT) or no‐tillage (NT). Phosphorus adsorption and desorption in undisturbed soil was studied by using a continuous flux system containing a P solution for adsorption measurements or deionized water and Mehlich‐I solution for desorption measurements. The Oxisol, which had higher clay, hematite, and goethite contents than the Ultisol, exhibited the highest maximum P adsorption capacity (P_max) values in disturbed samples. Also, the disturbed Ultisol samples had lower P_max values under NT than under CT. The undisturbed soil samples exhibited no significant differences in P adsorption between soil management systems, but P desorption was more marked under NT than under CT. The samples of Oxisol under NT exhibited lower P adsorption rates and higher P desorption rates than the CT samples of the same soil. The decreased P adsorption in undisturbed samples relative to disturbed samples suggests that P adsorption is influenced by physical properties of soil.     

Effect of moisture and temperature regimes on available phosphorus in wetland rice soils

Abstract

A laboratory experiment was conducted to evaluate the effects of water and temperature regimes on availability of soil phosphorus (P). Four soil samples with variable levels of available P collected from a long‐term P frequency trial were incubated under two moisture regimes, continuous waterlogging (CWL) and alternate wetting and drying (AWD) at 20°C and 30°C temperature for 90 days. The samples were extracted with 0.5M NaHCO₃ for available P determination after incubation. Increase in temperature increased available P content and this increase was more prominent in CWL conditions. Available P in all the soils tested was higher under CWL than AWD conditions, however, the increase in available P due to CWL environment was more pronounced in soils with higher available P.     

Evaluation of Pb and Ni Mobility to Groundwater in Calcareous Urban Soils of Ancona, Italy

This study was performed on 21 soils with the aim of establishing whether Pb and Ni adsorption/desorption parameters could be considered as good indicators of the risk of groundwater pollution. Results showed that high pH values in soil caused a totally irreversible Pb adsorption, thus excluding any risk of Pb groundwater pollution. Sorption/desorption studies, quantified by the desorption index (DI), showed that Ni retention was only partly affected by the basic pH values but it was also due to the electrostatic attraction processes occurring on soil surfaces, as demonstrated by the partial reversibility of the Ni sorbed. This justifies possible risks of Ni groundwater pollution. The results of a monitoring research confirmed these findings. Results suggested that the adsorption/desorption parameters, namely DI, are promising indicators to predict the risk of groundwater pollution from metals in calcareous soils.     

An Improved Procedure for Determining Magnesium Fertilizer Dissolution in Field Soils

Abstract

The sequential extraction procedure currently used to measure magnesium (Mg) fertilizer dissolution in soils consists of removing dissolved Mg (step 1), and partially dissolved Mg (step 2), followed by an 18‐h extraction with 2 M HCl at room temperature to determine undissolved Mg (step 3). This procedure is satisfactory for soluble and moderately soluble Mg fertilizers but is not an accurate procedure for slightly soluble fertilizers, such as serpentine. When step 3 is replaced by a digestion procedure using 2 M HCl for 4 h at 90–95°C (improved step 3), the total serpentine Mg recovery (dissolved and undissolved Mg) from soil samples, either immediately after serpentine was added to soil or after a 21‐day incubation with moist soil, was about 100% compared to 40–50% by the original procedure. The improved procedure also increased the recovery of serpentine Mg applied to field soils. Therefore, this study recommends that the third step of the sequential extraction procedure be replaced by a 4 h digestion using 2 M HCl (90–95°C).     

Determination of phosphate desorption characteristics in soils using successive resin extractions

Abstract

An alternative method for examining phosphate desorption characteristics in soil was tested. Five tropical soils with very different phosphate sorption capacities were incubated with added phosphate under three different conditions: 2 days at 25°C, 55 days at 25°C, and 2 days at 50°C. After incubation the phosphate was desorbed from the soil using successive cation‐anion resin extractions. The data from these extractions were fitted to a first order rate equation describing desorption. From the equation, an asymptote (B) was found to represent the ultimate amount of phosphate desorbable from each soil after incubation. It was found that increasing the incubation time or increasing the temperature of the incubation lowered this parameter ‘B’ suggesting that the slow reaction of adsorbed phosphate had reduced the amount of readily desorbable phosphate. Differences between soils as reflected in this parameter may indicate differences in the residual value of added phosphate in the field.     

Semi‐micro determination of total phosphorus in soils,sediments, and organic materials: A simplified perchloric acid digestion procedure

Abstract

A semi‐micro modification of perchloric acid digestion method for the determination of total P in soils, sediments, and organic materials is described. Samples are digested for 30 minutes with nitric acid at 115 °C and then for 2 hours with perchloric acid at 170 °C in an aluminum heating block. After dilution, samples are hydrolyzed at 100 °C for 1 hour in order to decompose pyrophosphate, and the liberated orthophosphate is determined without a neutralization step by the phosphomolybdate blue method of Murphy and Riley (1962). Comparability with the method of Sommers and Nelson (1972) is demonstrated using nine samples of different types. The same reaction conditions of digestion and color development as in the determination of total P in waters (Kopá?ek and Hejzlar, 1993) enable a comparable estimate of total P in solid and water samples in complex environmental studies.     

Phosphorus adsorption and desorption in a sandy soil amended with high rates of coal fly ash

Abstract

Amending sandy, drought‐prone soils with high rates of coal fly ash has the potential to improve plant growth by enhancing soil moisture relations. However, some studies have questioned the plant availability of native and fertilizer phosphorus (P) in ash‐amended soils. We used a batch adsorption study and a 42 day incubation study to examine the effects of amending an Evesboro loamy sand with fly ash (0–30%, w:w) on P availability and adsorption‐desorption. Fly ash increased soil test P from 13 mg/kg (soil) to 34 mg/kg (30% ash) but had little effect on readily desorbable P. The adsorption or desorption of P was not markedly influenced by fly ash in either batch or incubation studies except at the highest ash and P rates. In the batch study, the greatest increases in P adsorption were seen at the 20% and 30% ash rates and P equilibium concentrations >20 mg/L. Immediate and long‐term decreases in P desorption occurred in the incubation study at all ash rates when ≥500 mg P/kg were added but fly ash had little effect on P desorption at P rates ≤250 mg P/kg.     

Pentachlorophenol interactions with soil

Pentachlorophenol (PCP) adsorption and desorption equilibrium was studied with two Menfro silt loam soils — upper horizon and lower horizon. For the adsorption studies the variables were: temperature (10 and 30 °C) and the amount of organic matter. The variables for the desorption studies were: temperature (10 and 30 °C), pH and the presence of an anionic and a cationic surfactant. The results from these studies confirmed the importance of soil organic matter for adsorption of PCP on the soils. The adsorption data at different temperatures indicated the physical nature of the adsorption process. The desorption data produced non-singularity and some PCP was irreversibly adsorbed onto the soil despite repeated washings. Increased pH increased the desorption of PCP from the soil. The anionic surfactant, sodium dodecylbenzene sulfonate (SDS) was able to desorb significant amounts of PCP from the soil at doses equal to critical micelle concentration (CMC). But, the nonionic surfactant, surfactant, Triton X-405 required a much higher dose (twice the CMC) to cause a significant desorption of PCP from the soil.     

Enzyme activities in Appalachian soils: 3. Pyro‐phosphatase

Abstract

The pyrophosphatase (PPi) enzyme catalyzes the hydrolysis of pyrophosphate to orthophosphate. The PPi activity was determined in 14 hill‐land soils of the Appalachian Region. The top two horizons from each soil were sampled and stored in a field‐moist state at 4°C (4°C) and in an air‐dry (AD) state prior to determination of PPi activity. Each soil type had its own level of PPi activity. The mean PPi activities of surface and subsurface horizons stored at 4°C were 1.3 and 1.7 times higher than those of AD samples. The average PPi activities of surface horizons were 6.2 and 4.6 times higher than subsurface horizons stored at AD and 4°C. respectively. The PPi activities were positively correlated with organic C, N, forms of S and P. exchangeable cations, original moisture by weight and volume, and percent air‐filled porosity. In both surface and subsurface horizons, significant positive correlationships were observed between PPi activities and Mn content, indicating the need for Mn in the activation of PPi. High PPi activities in surface horizons might induce a greater rate of hydrolysis of applied pyrophosphate (polyphosphate) fertilizers to orthophosphate and lead to undesirable fixation of P in acid soils.     

An acid dichromate digestion procedure for total nitrogen determination in soils

Abstract

Modified version of a dichromate digestion procedure, earlier found suitable for simultaneous determination of organic carbon (C) and potentially mineralizable nitrogen (N) in soils, was evaluated for total N determination in 44 diverse soil samples from the semi‐arid region of India. The soils belonged to Vertisols and Alfisols and had a wide range in total N contents. The method involves digestion of the soil sample with an acidified dichromate solution for 30 minutes in a digestion tube in a block digester preheated to 165°C followed by determination of N in the digest by steam distillation procedure. The efficacy of the dichromate procedure for determining total N differed for the two soil types. Excellent correlations were observed between the values of total N obtained by the dichromate procedure (Dichro‐N) and by Kjeldahl method (Kjeldahl‐N) for Vertisols (R²=0.995; n=21) and Alfisols (R²=0.952; n=23). The regression equations describing the relationships between the two soil types can be used to estimate Kjeldahl‐N from Dichro‐N. Both Kjeldahl and the proposed acid dichromate methods were found to be more precise in determining total N in Vertisols than Alfisols. The proposed procedure is rapid and simple and can be used for routine total N determination especially, in soils such as Vertisols. Based on our results the acid digestion procedure certainly deserves a wider evaluation with a range of soil types.     

Effects of heating and autoclaving on sorption and desorption of phosphorus in some forest soils

A number of biological and chemical processes may affect soil phosphorus availability when forest fires occur, partly as a result of heating. We describe here a laboratory experiment to study the effects of soil heating on changes in sorption and desorption of P. Autoclaving was also included as an additional treatment of moist heating under pressure. Five forest soils (two Podzols, one Arenosol, one Luvisol and one Alisol) were heated to 60°C, 120°C and 250°C or autoclaved for 30 min. They were repeatedly extracted with Bray I and analysed for inorganic and organic P fractions. The desorbed P data were fitted to an asymptotic exponential equation to obtain the desorption rate and capacity parameters. Podzol and Arenosol soils showed a quick P desorption after heating, while Luvisol and Alisol soils showed a slow desorption rate. The immediate increase in available P that occurred after heating or autoclaving originated mostly from solubilisation of microbial metabolites and soil organic components. Autoclaving decreased P sorption capacity in all soils, but the effects of heating on P sorption differed among soils. Except for one of the soils, the low P-fixing soils (Podzol and Arenosol) showed a decrease in P sorption when heated to high temperatures, whereas the high P-fixing soils (Luvisol and Alisol) showed little changes after heating. Fire intensity and soil characteristics are important factors determining short-term and long-term soil P dynamics.     

Sorption and desorption of selenium in different soils of the mediterranean area

Abstract

The adsorption of selenium (Se) in the selenate form and its desorption by phosphate in four soils with different physiochemical properties were studied in the laboratory. To determine adsorption isotherms for selenate 25 mL of solutions containing 1 to 100 ppm of Se were added to 2.5 g of soil. Desorption isotherms were determined by resuspending the samples in phosphate solution. The selenate sorption process was adequately described by the Freundlich equation. In pine forest and woodland soils, characterized by the highest organic matter content and cation exchange capacity (CEC) values, the isotherms were classified as L type, since the amount of Se sorbed appeared to move towards saturation. The organic matter content played the most important part in the adsorption of Se, while pH appeared to have a small effect on the ability of the soil to adsorb Se. The high CaCO₃ content of the pine forest soil may have contributed in increasing the Se adsorption notwithstanding the high pH value. The cultivated and arable soils showed a reduced sorption capacity. The sorption could be described by an S type curve. At low concentrations of Se the affinity of the solid phase was less than that of the liquid phase. By increasing the concentration of Se in solution, the affinity of the solid phase increased and the sorption was favored. Selenate desorption by water was negligible, whereas the amount of Se desorbed by phosphate varied among the different soils. The desorption experiments indicated that a significant portion of the sorbed Se was irreversibly retained. This suggests the existence of linkages which allow the release of Se in the soil solution only after physico‐chemical variation such as exchange with phosphate ions.