Acid Soil Samples Research Articles

Ultrasensitive detection of trace Hg(Ⅱ) in acidic conditions using DMABR loaded on sepiolite: Function, application and mechanism studies

Fast and real-time detection of trace Hg(Ⅱ) by fluorescent probes under acidic conditions is urgently required due to the high toxicity and accessibility to creatures and human being. However, fluorescent probes for Hg(Ⅱ) detection in environmental samples are rarely reported due to the protonation potential of acidic mercury sources. In this study, the SD probe was developed by 5-(p-dimethylaminobenzylidene) rhodanine (DMABR) loaded on sepiolite by hydrothermal treatment, and showed excellent Hg(Ⅱ) detection performances for mercury sources at pH 4–10 due to buffering ability of the hyperconjugated lactam rings. Sepiolite functioned as the support skeleton to decrease intermolecular transition, and thus increased the sensitivity. At pH 4, the SD probe showed high selectivity and sensitivity for Hg(Ⅱ) among various species, with low LOD and binding constant of 4.78 × 10−9 M and 1.34 × 106 M−1, respectively. Through DFT calculations, MAS 1H NMR and 2D-COS analysis, the detection mechanism was demonstrated as SN1 substitution of the spontaneous leaving H on amino groups in the transient state during tautomeric equilibrium, rather than the expected high-affinity sulphydryl. Additionally, the SD probe exhibited promising potential in quantifying water-soluble and bioavailable Hg(Ⅱ) in acidic polluted soil and water samples. Moreover, real-time detection was realized by paper-based strips.

Magnetic Fe3O4 /Al2O3 /MnO2 ternary nanocomposite: Synthesis and characterization for phosphorus desorption from acidic soils using dialysis membrane tube

Monitoring phosphorus fertilization is crucial for controlling the concentration of biologically available soil P. Over the years, several methodologies have been used, including successive cropping in a greenhouse or field, as well as extractions employing P sink procedures. The latter procedures are ideal laboratory experiments to show the soil's ability to supply P and to explore the P-residual release kinetics. Following these methodologies, long-term P desorption studies have been developed using dialysis membrane tubes filled with nanomaterial solutions. In this study, a magnetic nanocomposite (Fe3O4/Al2O3/MnO2) was synthesized and characterized utilizing cutting-edge instruments such as XRD, FTIR, FAAS, BET, SEM, and EDX. The resulting material had a crystalline size and surface area of 22.75 nm and 203.69 m2/g, respectively, and was employed for long-term P-desorption and kinetics experiments while filled in dialysis membrane tubes. The P-desorption experiment was conducted on four separate acidic soil samples that were cultured for 122 days with four different P concentrations. The findings demonstrated a direct relationship between P-desorbed and P-treatment, as well as with desorption time. The minimum desorption was obtained from the control of Boji Dirmaji soil P0 (1.16–9.36) and the highest desorption from Nedjo soil with P3 (5.23–30.35 mg/kg) treatment over 1–28 days. The rate of P release from soil to solution or diffusion through the membrane was determined by pseudo-first-order kinetics with a rate constant (0.021–0.028 hr−1). This method has the potential to measure fixed-P availability by mimicking it as a plant would, with high P-desorption efficiency and quick P-release capacity.

Microorganism community composition analysis coupling with 15N tracer experiments reveals the nitrification rate and N2O emissions in low pH soils in Southern China.

Nitrification in agricultural soil is an important process for food production. In acidic soil, nitrification is however also considered to be a major source of N2O production. The nitrification rate largely depends on the community composition of ammonia-oxidizing organisms. To obtain a view of the nitrification rates and N2O emission situations in low pH soils in Southern China and understand their relations with the microbial community composition, here we conducted 15N tracer experiments and microorganism community composition analysis using four acidic agricultural soil samples collected in Southern China. A single dominant community (relative abundance >68%) of the ammonia-oxidizing bacteria and ammonia-oxidizing archaea was observed in the soils with pH = 4.81–6.02. A low amount of {text{NO}}_{3}^{mbox{--}}] was produced from the nitrification in the strongly acidic soil (pH = 4.03), and the calculated nitrification rate in this soil was significantly lower than those of other soils with pH = 4.81–6.02. High N2O emissions but low 15N–N2O emissions were observed in the soil with pH = 4.03. Our results suggest that, under aerobic conditions, soil pH is an important factor affecting nitrification through modifying the microorganism composition.

Threshold effects of soil pH on microbial co-occurrence structure in acidic and alkaline arable lands

Soil pH plays a pivotal role in shaping microbial diversity and community composition in terrestrial ecosystems. Soil microbes clearly do not exist independently and instead form complex interaction networks, but little is known about the effect of soil pH upon those microbial co-occurrence networks. In this study, 62 alkaline and 61 acidic soil samples were collected from the North China Plain to investigate the effect of soil pH on microbial co-occurrence structure. Most bacterial and fungal OTUs in acidic soils were maximally abundant at soil pH of ~5.5, while in alkaline soils the corresponding OTU abundance attainted its maximum at pH ~8.3. Unlike those OTU abundance distributions, the relationship between soil pH and the number of links between OTUs in the co-occurrence network was best fitted by convex curves, with the pH thresholds found at 5.39 for bacteria and 5.60 for fungi in acidic soils. In alkaline soils, a dip in the relationship (only for fungi) between soil pH and the links was also observed, with a pH threshold at 8.04 for bacteria and 8.28 for fungi. From the co-occurrence analysis we identified 37 core bacterial species (mainly in Actinobacteria and Proteobacteria) and 24 core fungal species (mainly in Ascomycota). Together, this study revealed the threshold effects of soil pH upon microbial co-occurrence structure and identified the core microbial species in the North China Plain. These findings provide baseline information in mediating soil microbial co-occurrence structure by adjusting soil pH and core species in croplands.

Acidophilic and Acid Tolerant Actinobacteria as New Sources of Antimicrobial Agents against Helicobacter Pylori.

About half of the world's population is infected by Helicobacter pylori, which is related to various diseases. The increase in the resistance of H. pylori to antibiotics is alarming and requires new medication candidates. In this study, 83 acidic soil samples (pH 3.9-6.8) were collected from tea and rice farms, located in the semitropical strip in the north of Iran (Lahijan and Fooman cities, Gilan Province). After various pretreatments, including dry heating (120 oC, 10 min), exposure to electromagnetic waves (800 Hz, 3 min), and centrifuging (2950 g, 15 min), 33 acidophilic or acid-tolerant actinobacteria were isolated and their potentials as a source of active metabolites against H. pylori were investigated. According to phenotypic and molecular identification tests, the actinobacterial isolates were classified into Streptomyces and Kitasatospora genera. Among 10 strains that had anti-H. pylori activity, the highest potentials were seen in the strains UTMC 3061 and UTMC 3318. The minimum inhibitory concentrations (MIC) of the related metabolites were 125 and 62.5 µg/ml, respectively. In the checkerboard test, the metabolites of these actinobacteria showed synergism with clarithromycin and reduced its MIC from 1 to 0.5 µg/ml. However, no synergism was seen between the metabolites and amoxicillin or metronidazole. The gas chromatography-mass spectrometry (GC-MS) analysis of the metabolites showed some antimicrobial agents, including carbamic acid, maltol, 2.4-di-tert-butylphenol, methyl dimendone, prolylleucyl, and oleamide. The strains UTMC 3061 and UTMC 3318 showed 99.41 and 100% similarity in 16S rRNA gene sequence to Streptomyces spinoverrucosus and Streptomyces cirratus, respectively. Their metabolites showed good antibiotic activity and limited toxicity and can be considered as promising sources of natural products against H. pylori.

Biochar effects on phosphorus sorption-desorption kinetics in soils with dissimilar acidity

To describe phosphorus (P) dynamics with progressing reaction time entails an adequate understanding of P sorption and desorption kinetics in soils. To this end, the present study examined P sorption and desorption kinetics via batch experiments in four different soils with dissimilar acidity that were incubated for 90 days with 6% (w/w) wheat straw-derived biochars produced at 300 (B300) and 600 °C (B600). P sorption and desorption kinetics were measured in incubated soils and fitted to several models (zero, -first, -second-order, parabolic diffusion, simple Elovich, and exponential equations). Based on the results, the properties of wheat straw-derived biochars were affected by the pyrolysis temperature. The time required to reach the near-equilibrium state of incubated soils was about 48 and 24 h for P sorption and desorption kinetic experiments, respectively. Moreover, as pyrolysis temperature rose from 300 to 600 °C, P sorption and desorption decreased and increased, respectively in acidic soil samples (pH 4.6 and 6.0). An opposite result was obtained for the alkaline soil (pH 8.3). Adding B300 to the alkaline soil (pH 7.4) decreased P sorption, but increased P desorption. On the contrary, B600-treated alkaline soil (pH 7.4) demonstrated a slight increase in P sorption, although with a marked reduction in P desorption. P sorption kinetics was found to successfully follow simple Elovich, pseudo-second-order, and exponential models. Similarly, P desorption kinetics were duly described by pseudo-second and first-order and simple Elovich equations. The findings of the study confirmed that biochar application and pyrolysis temperature influence P sorption and desorption kinetics in soils and these effects were most likely determined by soil reaction. All this can bear implications for further studies on biochar applications and P sorption-desorption kinetics.

Effectiveness of nanoscale zero-valent iron for the immobilization of Cu and/or Ni in water and soil samples

In the last few years, the effectiveness of nanoscale zero-valent iron (nZVI) as a treatment for polluted waters and soils has been widely studied. However, little data are available on its efficacy for metal immobilization at low and moderate doses. In this study, the effectiveness of two doses of commercial nZVI (1 and 5%) to immobilize Cu and/or Ni in water and acidic soil samples was evaluated. The influence of the nanoremediation technology on iron availability, physico-chemical soil properties and soil phytotoxicity was also assessed. The results show that the effectiveness of nZVI to immobilize Cu and Ni in water and soil samples was determined by the dose of the nanomaterial and the presence of both metals. Nickel immobilization was significantly decreased by the presence of Cu but the opposite effect was not observed. nZVI showed better immobilization capacity in water than in soil samples. In water, the dose of 5% completely removed both metals, whereas at a lower dose (1%) the percentage of immobilized metal decreased, especially for Ni in Cu + Ni samples. In soil samples, 5% nZVI was more effective in immobilizing Ni than Cu, with a 54% and 21% reduction of leachability, respectively, in single contaminated samples. In Cu + Ni soil samples, nZVI treatment led to a significant decrease in Ni immobilization, similar to that observed in water samples. The application of nZVI induced a dose-dependent increase in available Fe—a relevant effect in the context of soil rehabilitation. Germination assays of Medicago sativa and Vicia sativa seeds revealed that treatment with nZVI did not induce phytotoxicity under the experimental conditions tested, and that the phytotoxicity induced by Ni decreased significantly after the treatment. Thus, the use of nZVI emerges as an interesting option for Cu and/or Ni immobilization in water samples. The effectiveness of nZVI to remove Cu from acidic soil samples was moderate, while for Ni it was strongly dependent on the presence of Cu. These observations therefore indicate that the results in water samples cannot be extrapolated to soil samples.

Impact of acidic volcanic emissions on ash leaching and on the bioavailability and mobility of trace metals in soils of Mt Etna

We report on original geochemical data, which combine the rainfall trace metal contents from three different areas of Mt. Etna, variably fumigated by the volcanic plume, and those from soils, collected over the whole volcano. Trace element contents in rainfall appear mostly related to acidic ash leaching, while only for the most volatile elements (Cu, Zn, Cd, Pb, As, Sb, Tl, Se) we suggest a derivation from magmatic degassing. We analyzed separately the labile fraction of soil samples, considered the fraction bioavailable to plants and soil organisms living in. The complexing medium used to extract the bioavailable fraction simulates the growth environment of plant roots.The contents of trace elements in the bioavailable fraction from soil samples showed peculiar patterns, apparently unrelated to the plume fumigation. The transition metal contents in the bioavailable fraction account for less than 15 % of the pseudo-total fraction and the highest contents were measured in the less acidic soil samples and farthest from the summit craters. In particular, high Fe, Mn, Co, Ni, Pb, Zn, Cd contents were paralleled by high soil organic carbon concentrations, which increased in the samples collected downwind the summit vents. Concerning immobile elements, their abundance in the bioavailable fraction was related to the degree of alteration of soils. Two elements, Se and Tl, were enriched in soil samples collected at closer distance from the summit vents. Their origin is probably related to the plume deposition.The study highlighted that the accessibility of plants to potentially harmful trace elements present in the soil is not simply related to the exposure to pollutants, but also to their fate in the pedogenetic environment.

Distribution of different forms of acidity in some lateritic soils of Purulia district of West Bengal

Twenty four acid soil samples collected from six blocks of Purulia district representing part of red and lateritic belt of West Bengal and Alfisols soil order were analysed to characterise their nature of acidity and their relationship with soil properties. The mean values of total acidity (TA), hydrolytic acidity (HA) and exchange acidity (EA) were 1.91, 1.53 and 0.38 cmol (p+) kg-1 which were ranged from 1.35-2.59, 1.20-1.94 and 0.15-0.65 cmol (p+) kg-1 respectively. On an average, the contribution of electrostatically bound aluminium (Al3+) and hydrogen (H+) to exchange acidity varied from 60.0-80.0 and 20.0-40.0 per cent with the mean values of 70.42 and 29.58 per cent respectively. The different types of acidity were significantly and positively correlated with organic C, clay content and CEC of soil but negatively correlated with soil reaction (pHw and pHca). They also showed significant positive correlations with each other.

Optimization of Lignite Particle Size for Stabilization of Trivalent Chromium in Soils

ABSTRACTStabilization capacity of 5% by weight lignite added in three particle size ranges (<0.5; 0.5–1.0 and 1.0–2.0 mm) to acidic (pH = 5.0) or calcareous (pH = 7.7) sandy soil samples of <2 mm grain size artificially contaminated with 375 mg/kg Cr(III) was assessed through fit-for-purpose leaching tests performed with CH3COOH, NH2OH·HCl and EDTA. About 90% and 60% of Cr(III) were immobilized in calcareous and acidic soils per se, respectively. Although the point of zero charge measurements (pHpZC≈4.5) indicated that lignite could effectively bind positively charged Cr hydroxo complexes at the pH of the calcareous soil, the application of lignite is unnecessary due to the low solubility of these species. Although the acidic soil mobilizes Cr, the addition of lignite has been proven to stabilize it. The phytoavailable Cr fraction in the soils per se was about 10–25%. In spite of the mobilization of Cr by acidic soil, the phytoavailable Cr concentration decreased to about half when the lignite particle size was either 0.5–1.0 or 1.0–2.0 mm. Lignite was suitable for Cr stabilization in acidic soil in a close particle size range, ensuring the dispersibility needed to enhance efficient Cr transfer from the contaminated soil to the stabilizer.

Utilization of Anthocyanin Extracted from Pletekan (Ruelliatuberosa L.) in Determination Soil pH

Pletekan (Ruelliatuberosa L.) is a flowering plant that grows wild. Pletekan has blue-purple flowers, containing the anthocyanin as its specific color. Anthocyanin is an organic material that can be used as an indicator of natural acid alkali, because the color of anthocyanin can ensure specific color changes when it reacts with materials at a certain pH as well. This research aimed to utilize anthocyanin extracted from pletekan as a determinant of soil pH. The used method was maceration extraction by soaking fresh pletekan flowers using maceration solvent (methanol acidified by HCl 1%) for 2-3 days. Concentrated anthocyanin extracts needed to be diluted with extracts that had not been concentrated so that the resulted color changes were more specific. The anthocyanin mixture was applied to pH 1-12 buffer solution and in acid and alkaline soil samples. The soil was dissolved using aquadest at a ratio of 1: 2, the soil was left to settle to get water. The color change in the tested water of soil sample was adjusted to the color of the buffer solution and pH meter. Results showed that color change of soil sediment-water which was dropped by natural pH indicators needed more indicator drops such as 2-3 levels than was color changes caused by the buffer solution.

Effect of liming and applied phosphorus on growth and P uptake of maize (Zea mays subsp.) plant grown in acid soils of West Wollega, Ethiopia

The study aimed at investigating effects of lime and mineral P fertilizers on P uptake and growth of maize (Zea mays subsp.) in greenhouse pot experiment. Combination of four P rates and four lime rates were applied to four highly acidic soil samples and the soils were incubated for a total of 112 days after which maize (Zea mays subsp.) was planted. The maize plants were harvested for analysis after 42 days of growth. Control experiments were also included. Available P (Bray I) and pH were significantly increased after incubation. Maximum available P was obtained in the soils that received the highest P rate and optimum lime rate. Levels of exchangeable acidity were significantly decreased in the P and lime treated soils compared to the control experiments. Plant biomasses and P uptake of maize increased significantly (p ≤ 0.001) with application of P and lime compared to the control experiments.

Influence of Zn, Cd, and Cu fractions on enzymatic activity of arable soils

The aim of this study was to investigate the heavy metal effect on enzymatic activity in acidic soil samples during spring, summer, and autumn. The four metal fractions, acid-soluble and exchangeable (F1), reducible (F2), oxidizable (F3), and residual (F4) using BCR method in soil samples, were evaluated. The highest percentage share of zinc and copper was determined in F4 (45.8, 54.9%, respectively) and cadmium in F3 (45.6%). The enzymatic activity in soil was differentiated in seasons. During spring, the significant relationship was noted between F1/zinc/dehydrogenase, during summer F2/cadmium/phosphatase as well as F4/cadmium/dehydrogenase and autumn F3/zinc/dehydrogenase. Fraction F1/zinc/copper influenced phosphatase activity, whereas F3/Zn increased dehydrogenase and F2/Cd protease activity. The results indicate that the heavy metals affected dehydrogenase activity the most.

Ethylene coordinates seed germination behavior in response to low soil pH in Stylosanthes humilis

Stylosanthes humilis is known to exhibit high persistence in acid soils, however, how low soil pH controls seed germination as well as root and hypocotyl growth remains unknown. This study was carried out to evaluate the hormonal and metabolic alterations induced by low soil pH on seed germination behavior of S. humilis. Seeds of S. humilis were sown in acid soil samples or sand soaked in buffer solution with pH ranging from 4.0 to 7.0. Concentrations of indole-3-acetic acid, ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), primary metabolite profile and final seed germination were evaluated after four days. Low soil pH led to increased final seed germination, concomitantly with higher root penetration into the soil as well as higher ACC and ethylene production by seedlings. Treatment with the ethylene biosynthesis inhibitor L-α-(2-aminoethoxyvinyl)-glycine (AVG) greatly reduced final seed germination under acidic conditions. Final seed germination of seeds treated with AVG was increased by exogenous ethylene application in a dose-dependent manner. Furthermore, low soil pH promoted distinct changes in IAA concentrations, and in carbon and nitrogen metabolism in hypocotyl and roots. Low soil pH increases the final germination of S. humilis seeds through alterations in ethylene metabolism, allowing root penetration into the soil.

English

Understanding of phosphorus (P) retention and release mechanisms provides crucial information for the effective management of phosphorus to enhance crop production and sustain soil. In acidic soil, available phosphorus is fixed by aluminum and iron. To overcome this problem, soils are limed to fix aluminum and iron. But this practice is not economical for small scale farmers and also it is not environmentally friendly. This study was conducted to improve phosphorus availability using biochar produced from coffee husk and corn cob to fix aluminum and iron instead of phosphorus. Acidic soil samples were mixed with biochar applied at the rates of 0, 5, 10 and 15 t ha-1 and incubated in laboratory for 2 months at ambient temperature. The results showed significant effects (p<0.01) on selected soil chemical properties by increasing soil pH and reduced exchangeable acidity, exchangeable aluminum, and exchangeable iron in a way that enhanced the availability of phosphorus. Due to the incorporation of biochar the available P level increased to a level ranging 3.64±0.34 -23.21±0.07 mg/kg after an incubation period of 2 months and it increased by 84.3% available phosphorus when coffee husk biochar produced at 500°C temperature was applied at a rate of 15t/ha. Moreover, further field researches are needed to evaluate the effect of biochar on availability, the fate and uptake of available P in soil. Key words: Fixation, biochar, feedstock, acidic soil, pyrolysis temperature.

Extractants for available boron in limed acid soils and its correlation in crops with high carbon storage capacity (Tectona grandis)

ABSTRACTThe objective of this work was to evaluate the efficiency of six extractants for available boron in acid soils undergoing to liming, and to correlate the results of soil analysis with foliar response seen in the teak plants in greenhouse conditions. Acid soil samples were collected and their chemical characterization was performed using standard analysis protocols. Later, agricultural lime was added to the experimental units in greenhouse conditions in order to control the soil acidity and these were incubated for 30 days. Six extracts for available boron were evaluated and correlated with response in the plant by foliar analysis. It is concluded that a high dissolution power of boron extractant solution produces a high sensitive in the determination of the changes of boron concentration in the limed acid soil. These methods are seen to be not adequate for the determination of available boron contents at high concentrations.

Phosphorus Status, Inorganic Phosphorus Forms, and Other Physicochemical Properties of Acid Soils of Farta District, Northwestern Highlands of Ethiopia

Soil acidity and low availability of P limit crop production in the highlands of Ethiopia. The objective of this study was to determine the P status, distribution and forms of inorganic P and relate them to selected chemical properties of eight representative acidic surface soil samples from Farta District. Soil pH (H2O) varied between 4.74 and 5.50. The moderate to high CEC suggests that besides kaolinite, the soils also contain expandable 2 : 1 clay minerals. Though the total P content was high, the available Olsen P content was very low or low in all soils except one. In most soils, the abundance of inorganic P fractions was as follows: P bound by oxalate extractable iron (Feox-P)&gt;reductant soluble Fe-P&gt;occluded Al-Fe-P&gt;P bound by oxalate extractable aluminum (Alox-P)&gt;calcium bound P (Ca-P). Olsen P had a very strong positive correlation (P≤0.01) withAlox-P (r=0.98),Feox-P (r=0.96), and oxalate extractable P (r=0.94). Though Fe bound P reserves were quite abundant and the degree of P saturation ofAlox+Feox(median 3.3%) was moderate, the extremely low P saturation ofAlox(median 0.5%) explains the P deficiency of the soils.

A rapid procedure to calculate lime requirements based on single titration with base

The lime requirement (LR) in 39 surface acid soil samples (0–30 cm) from western Greece was calculated using a single-addition titration of successive 3-mL 0.022 M calcium hydroxide [Ca(OH)2]. Soil pH measurements and titrations were performed in soil/water (1:2) and in a soil/0.01 M CaCl2 (1:2) suspension while being stirred. The results were referred to as ‘pH data group I’ and ‘pH data group II’, respectively. In each ‘pH data group’, the samples were separated into ‘pH data subgroups’, according to the total volume (mL) of 0.022 M Ca(OH)2 added to increase the initial pH (pHa) to a target value of 6.5 (pHt). The fitted linear regression equation pHt = b × volume + pHa was used for each ‘pH data group’ to determine the slope b. The b-weighted mean for each ‘pH data group’ was calculated. The LR was then calculated as follows: Mg CaCO3 ha−1 = 0.495 (pHt – pHa)/b, where b is the average weighted mean from the two ‘pH data groups’ and is equal to 0.227. The validity of the above equation was confirmed after incubation with Ca(OH)2 for 72 h. This procedure is simple and gives a rapid and accurate estimation of LR with respect to the environment.

Sorption of atrazine and phenanthrene by organic matter fractions in soil and sediment

Atrazine and phenanthrene (Phen) sorption by nonhydrolyzable carbon (NHC), black carbon (BC), humic acid (HA) and whole sediment and soil samples was examined. Atrazine sorption isotherms were nearly linear. The single-point organic carbon (OC)-normalized distribution coefficients ( K OC) of atrazine for the isolated HA1, NHC1 and BC1 from sediment 1 (ST1) were 36, 550, and 1470 times greater than that of ST1, respectively, indicating the importance of sediment organic matter, particularly the condensed fractions (NHC and BC). Similar sorption capacity of atrazine and Phen by NHC but different isotherm nonlinearity indicated different sorption domains due to their different structure and hydrophobicity. The positive relationship between (O + N)/C ratios of NHC and atrazine log K OC at low concentration suggests H-bonding interactions. This study shows that sediment is probably a less effective sorbent for atrazine than Phen, implying that atrazine applied in sediments or soils may be likely to leach into groundwater.

Diffusion-induced changes on exchangeable and organic bound copper fractions in acid soil samples enriched with copper

Transport-induced changes in the concentrations of NH 4Cl (Cu E) and Na-pyrophosphate (Cu P) extractable Cu in acid soils were studied by using diffusion cells in order to quantify Cu transport by measuring the variation of Cu E and Cu P in a half-cell with no copper added (receiving half-cell). An empirical approach based on the Freundlich equation was used to describe the relationship between Cu in the soil water extract, Cu E, and Cu P. After 30 d of diffusion, Cu E and Cu P in the receiving half-cells increased from 0.2 to 2.6% and from 4.1 to 24%, respectively, relative to their hypothetical concentrations after infinite time. Copper transport was found to be influenced by the nature of the soil and its moisture content. Diffusion was modeled in order to calculate the increase in Cu E and Cu P in the receiving half-cell, which were assumed to be in equilibrium with Cu in the soil water extract. Nonlinear retardation in the diffusive transport model was implemented by using the Freundlich equation to obtain nonlinear effective diffusion coefficients for each Cu fraction. The results of the simulations were consistent with their experimental counterparts, which suggests that the moisture content and retardation used in the model provide reasonable estimations of the increase in Cu P in acid soils.