In-Situ Remediation of Lead–Zinc Polymetallic Mine Contaminated Soils by MnFe2O4 Microparticles

In-situ remediation is a practical approach to remediate soils contaminated with heavy metals. The MnFe₂O₄ microparticles (MM) were prepared for the in-situ remediation of contaminated soils from a lead–zinc polymetallic mine in Inner Mongolia province, China. The effects of MM dosage, pH on remediation efficiency, were determined with static vibration leaching experiment, and the release risk of heavy metals of treated soil was studied by column leaching experiment. The results showed that the leached Cu, Pb, Zn, and As concentration decreased drastically with increasing MM dosage, when the dosage was lower than 10 g/kg. Moreover, the decrease of pH caused increase of leached concentration of Cu, Pb, Zn, but slight decrease of leached As concentration. For the amended soil, concentrations of leached heavy metals were lower than Grade III limit of Chinese Environmental Quality Standards for Ground and Surface water (GB3838-2002) under simulated acid rain leaching condition. In comparison with non-amended soils, the total amount of Cu, Pb, Zn, and As release from amended soils was reduced by 93.6%, 69.2%, 57.0%, and 99.7%, respectively. The MM is a kind of promising amendment for heavy metals contaminated soil.     

Speciation and mobility of lead in shooting range soils

The mobility and bioavailability of lead (Pb) in seven military shooting range soils found in eastern and north eastern Botswana were studied using sequential extraction procedure. The different forms of Pb and their reactivity in the soil help explain their speciation, mobility and bioavailability in the environment. Mobility of Pb in the berm soils in all the seven shooting ranges was found to be over 90% implying high Pb lability. The bioavailability index of Pb was in the range 60–90%, an indication that most of the Pb can be available for plant uptake. Sequential extraction studies indicate that the partitioning of Pb was mostly confined to the carbonate compartment in all the shooting ranges. All the seven shooting ranges failed the Synthetic Precipitation Leaching Procedure (SPLP) with SPLP Pb concentrations exceeding United States Environmental Protection Agency (USEPA) 0.015 mg/kg critical level of hazardous waste, posing a pollution threat to surface and groundwater.     

Leaching Behavior of Heavy Metals and Transformation of Their Speciation in Polluted Soil Receiving Simulated Acid Rain

Heavy metals that leach from contaminated soils under acid rain are of increasing concern. In this study, simulated acid rain (SAR) was pumped through columns of artificially contaminated purple soil. Column leaching tests and sequential extraction were conducted for the heavy metals Cu, Pb, Cd, and Zn to determine the extent of their leaching as well as to examine the transformation of their speciation in the artificially contaminated soil columns. Results showed that the maximum leachate concentrations of Cu, Pb, Cd, and Zn were less than those specified in the Chinese Quality Standards for Groundwater (Grade IV), thereby suggesting that the heavy metals that leached from the polluted purple soil receiving acid rain may not pose as risks to water quality. Most of the Pb and Cd leachate concentrations were below their detection limits. By contrast, higher Cu and Zn leachate concentrations were found because they were released by the soil in larger amounts as compared with those of Pb and Cd. The differences in the Cu and Zn leachate concentrations between the controls (SAR at pH 5.6) and the treatments (SAR at pH 3.0 and 4.5) were significant. Similar trends were observed in the total leached amounts of Cu and Zn. The proportions of Cu, Pb, Cd, and Zn in the EXC and OX fractions were generally increased after the leaching experiment at three pH levels, whereas those of the RES, OM, and CAR fractions were slightly decreased. Acid rain favors the leaching of heavy metals from the contaminated purple soil and makes the heavy metal fractions become more labile. Moreover, a pH decrease from 5.6 to 3.0 significantly enhanced such effects.     

基于大麦根伸长测定土壤Pb毒性阈值、淋洗因子及其预测模型

选取了我国10个典型的不同性质农田土壤,外源添加8个不同Pb浓度,分别进行淋洗与非淋洗处理,根据ISO 11269-1根伸长毒性测试方法,测定了土壤外源Pb对大麦根伸长的毒性阈值(EC₁₀、EC₅₀)及Pb毒性的淋洗因子,同时建立了基于不同土壤性质的Pb毒性阈值预测模型. 结果表明: 不同性质土壤中Pb对大麦根伸长的毒性阈值有显著差异(P<0.01),EC₅₀ 值在300～4130 mg·kg^-1,EC₁₀ 值在55～633 mg·kg^-1. 淋洗处理明显降低了土壤中外源Pb的毒性,基于EC₅₀和EC₁₀测定的不同土壤淋洗因子(LF_ECx)的变化范围分别为0.96～1.96(LF_EC50)和1.03～1.81(LF_EC10). 相比而言,在酸性(pH<6.81)土壤中,淋洗处理对降低土壤外源Pb的毒性作用更为明显. 基于主控因子(pH、有机碳含量OC、阳离子交换量CEC)的淋洗与非淋洗土壤中Pb的大麦根伸长毒性(EC_x,_x=10,50)预测模型表明,除了江西红壤外,淋洗与非淋洗土壤中Pb的EC₅₀实测值均落在模型预测值±2倍标准误差范围之内,说明基于上述土壤主要性质可以较好预测不同性质土壤中Pb的毒性阈值.     

A Counter-Current Acid Leaching Process for the Remediation of Contaminated Soils from a Small-Arms Shooting Range

The objective of this research was to use a counter-current leaching process (CCLP) with leachate treatment to develop a remediation process for contaminated soils at a small-arms shooting range (SASR). The soil contaminant concentrations were 245 mg Cu kg^?1, 3,368 mg Pb kg^?1, 73 mg Sb kg^?1, and 177 mg Zn kg^?1. The CCLP includes three acid leaching steps (1M H₂SO₄ + 4M NaCl, t = 1 h, T = 20°C, soil suspension = 100 g L^?1), followed by one water rinsing step (1 h). Seven counter-current remediation cycles were completed, and the average resulting metal removals were 93.2 ± 3.5% of Cu, 91.5 ± 5.7% of Pb, 82.2 ± 10.9% of Sb, and 30.0 ± 11.4% of Zn. The metal leaching performances decreased with the number of completed cycles. Soil treated with the CCLP with leachate treatment process met the USEPA threshold criteria of 5 mg Pb L^?1 in the TCLP leachate. The CCLP allows a decrease of the water use by 32.9 m³ t^?1 and the chemicals’ consumption by approximately 2,650 kg H₂SO₄, 6,014 kg NaCl, and 1,150 kg NaOH per ton of treated soil, in comparison to standard leaching processes. This corresponds to 78%, 69%, 83%, and 67% of reduction, respectively.     

Reducing the Leachability and Bioaccessibility of Arsenic in Soils using Supported Nano Titanium Dioxide

We herein report the development and testing of a novel material, namely activated carbon-supported nano titanium dioxide (ACTD) for the immobilization of arsenic in soil. This material, which was prepared using a sol-gel method, effectively reduced the toxicity characteristic leaching procedure (TCLP) leachability and physiologically based extraction test (PBET) bioaccessibility of As(III) in soil samples. Upon processing the soils for 56 d at an ACTD dosage of 0.25 mmol g^?1, the TCLP leachability of As(III) was reduced by 82.7–97.7%, while the bioaccessibility was lowered by 58.6–81.2%. In addition, sequential extraction resulted in an 11.5–96.0% decrease in the mobile-As(III) and the mobilizable-As(III) fractions, but an increase in the residual-As(III) fraction upon treatment with ACTD. These observations indicate that the application of ACTD could result in an 80% reduction in As(III) environmental leaching, thereby confirming that ACTD appears suitable for the treatment of arsenic-contaminated soil.     

Stabilization Pb,Zn, and Cd-Contaminated Soil By Means of Natural Zeolite

This article aims to investigate the stabilization of Pb, Zn, and Cd contained in contaminated soil from a former mining site in Montevecchio, Sardinia, using clinoptilolite-rich tuff from Pentalofos, Evros. The study included (1) batch experiments and their environmental characterization and (2) column experiments. The first tests involved 1-month pot experiments with varying soil-zeolite mixtures, and their evaluation was carried out by standard USEPA leaching tests (TCLP, EPT test, SPLP). Moderate solubility reductions were recorded according to the TCLP (Pb: 38%, Zn: 33%, and Cd: 32%) due to the introduction of competing Na ions in the solution, while the EPT test showed more significant variations (Pb: 55%, Zn: 74%, and Cd: 46%). A major decrease is achieved in both cases by 10% w/w zeolite addition. The study was complemented by column experiments involving soil-zeolite mixtures eluted by CH3COOH solutions (0.003N and 0.05N). The solubility of Pb was reduced by 50 to 60% compared with the control column, thus indicating the considerable selectivity of clinoptilolite for Pb. In addition, Na and Ca measurements in the leachates confirmed that the immobilization of Pb was mainly attributed to ion exchange reactions.     

Assessment of a heavy metals‐contaminated site using sequential extraction,TCLP, and risk assessment techniques

The mobility of selected heavy metals in contaminated soil at a previous industrial site in Brisbane, Australia, was assessed using a sequential extraction technique. Copper, Pb, Zn, Cr, Fe, and Mn were extracted from the soil solution/exchangeable, carbonate, Fe and Mn oxides, and organic matter fractions. The amounts of metals adsorbed by these fractions were used as an indicator of each metal's mobility in the soil. Copper and Pb were largely adsorbed by the organic and oxide fractions, while a significant amount of Zn was extracted from the carbonate fraction. The potential mobility and biological availability of the metals in these soils is Zn > Cr = Cu ≈ Pb. Soils were also analyzed using the toxicity characteristic leaching procedure (TCLP) to determine whether the contaminated soil could be disposed of by landfilling. The leachability of all metals from the soils was very low, with metal concentrations below the allowable limits. The TCLP also showed that Zn was the most mobile metal in these soils. An environmental and health risk assessment was undertaken, and it was concluded that the site did not represent a risk despite the “total”; concentrations of some metals being up to 40 times the investigation threshold value adopted in Australia.     

Variation of Cu and Zn Fractionation and Mobility in Mine Tailing Soil Due to Experimental Leaching

The aims of this paper were to assess the variation of heavy metal (Cu and Zn) fractions and mobility in abandoned metal mine soil due to batch experimental leaching. Four solutions with different pH levels were used in the experiments. The total and fractional concentrations of heavy metals in untreated and leached soils were determined. The Kruskal–Wallis test was applied to verify the differences in the Cu and Zn distribution in soils before and after leaching. In order to assess the mobility of heavy metals, mobility factors (MFs) were calculated. The research results showed that the original/untreated soil was mainly of a sandy texture and acidic in character. After batch leaching for 7 days, the distribution of heavy metals was dominant in the residual fraction (F5). Heavy metal fractions in F1, F2, F3, and F5 showed a decreasing trend, but an increasing trend in F4 was observed. Among the solutions applied having different pH values, HCl (pH 3) illustrated the strongest effect on decreasing heavy metals in short-term mobile fractions (F1 and F2). The MF of Zn decreased more than that of Cu after 7-day batch leaching.     

Enhanced Soil Washing for the Remediation of a Brownfield Polluted by Pyrite Ash

Soil from an abandoned/disused fertilizer plant polluted with pyrite ash containing heavy metal(loid)s (As, Cu, Pb, and Zn) was treated by means of physical and chemical washing. We first performed an exhaustive characterization of the soil-pollutant interaction, which allowed us to determine the chemical nature (complex oxyhydroxides), potential mobility and bioavailability of the pollutants (very low), as well as the grain size fractions of preferential accumulation (silt-clay fraction comprises more than 60% of the material and revealed contents well above 2.000 ppm of Cu, Zn and Pb). Soil/ash samples were subjected to a number of chemical washing trials, including leaching with 2 M HCl, 2 M NaOH and acidic process water (pH around 0). The fraction below 63 µm was mechanically separated and exposed to additional leaching tests e.g. chloridizing roasting with NaCl plus water leaching. Of all the tested procedures, the latter proved the most effective, particularly with regard to Cu and Zn recovery (recoveries up to 40% and 34%, respectively). The information gathered offers an insight into the modes and rates at which metals can be leached from pyrite ashes after chloridizing roasting as a prelude to more extensive soil washing feasibility studies focused on potential metal recovery.     

Mobility and Distribution of Zinc,Cadmium and Lead in Calcareous Soils Receiving Spiked Sewage Sludge

Leaching column experiments were conducted to determine the degree of mobility and the distribution of zinc (Zn), cadmium (Cd), and lead (Pb) because of an application of spiked sewage sludge in calcareous soils. A total of 20 leaching columns were set up for four calcareous soils. Each column was leached with one of these inflows: sewage sludge (only for two soils), spiked sewage sludge, or artificial well water (control). The columns were irrigated with spiked sewage sludge containing 8.5 mg Zn l^?1, 8.5 mg Cd l^?1, and 170 mg Pb l^?1 and then allowed to equilibrate for 30 days. At the end of leaching experiments, soil samples from each column were divided into 18 layers, each being 1 cm down to 6 cm and 2 cm below that, and analyzed for total and extractable Zn, Cd and Pb. The fractionation of the heavy metals in the top three layers of the surface soil samples was investigated by the sequential extraction method. Spiked sewage sludge had little effect on metal mobility. In all soils, the surface soil layers (0-1 cm) of the columns receiving spiked sewage sludge had significantly higher concentrations of total Zn, Cd and Pb than control soils. Concentration of the heavy metals declined significantly with depth. The mobility of Zn was usually greater than Cd and Pb. The proportion of exchangeable heavy metals in soils receiving spiked sewage sludge was significantly higher than that found in the control columns. Sequential extraction results showed that in native soils the major proportion of Zn and Pb was associated with residual (RES) and organic matter (OM) fractions and major proportion of Cd was associated with carbonate (CARB) fraction, whereas after leaching with spiked sewage sludge, the major proportion of Zn and Pb was associated with Fe-oxcide (FEO), RES, and CARB fractions and major proportion of Cd was associated with CARB, RES and exchangeable (EXCH) fractions. Based on relative percent, Cd in the EXCH fraction was higher than Zn and Pb in soils leached with spiked sewage sludge.     

Heavy metal (Pb) accumulation in metallophytes as influenced by the variations in rhizospheric and non-rhizospheric soils physico-chemical characteristics

Activities at root-soil interface determine the solubility and uptake of metals by plants. Metal accumulation in plant species (Imperata cylindrical, Cynodon dactylon, Eleucine indica, Gomphrena celosoides, Sporobolus pyramidalis, Chromolaena odorata and Rhynchospora corymbosa) growing on Pb contaminated site as influenced by variations in physico-chemical characteristics, dissolved organic matter (DOM), Pb fractionation and different functional groups (using Fourier Transmittance Infra-red) of rhizospheric and non-rhizospheric soils was assessed. The electrical conductivity (2660–5520 µs) and Pb concentrations (51390.0–64080.0 mg/kg) were more in non-rhizospheric than rhizospheric soils having 276 µs to 3160 µs EC and 3289.0 to 44850.0 mg/kg Pb. More nutrients, DOM and carbohydrates functional groups (C-O; 1100 -1000 and O-H; 3700–3600) were found in rhizospheric compared to non-rhizospheric soils. The pH was slightly acidic (5.0–5.54) and E. indica with the lowest pH (5.0) accumulated highest Pb concentrations in shoot (8030 mg/kg) and root (16380 mg/kg) while C. odorata with highest values of pH, P, Ca and Mg in rhizospheric soil accumulated the least (root; 331.6 and shoot: 209.0 mg/kg). Pb was more in organic and residual fractions of rhizospheric and non-rhizospheric soils respectively. Reduction in pH, EC coupled with nutrients and DOM availability increased Pb uptake by plants.     

Persistence of D.D.T. and Benzene Hexachloride in Soils

Acid and alkaline soils, both alone and mixed with 2 % of D.D.T. or 2 % of benzene hexa-chloride (mixed isomers, containing 10% of the γ-isomer) have been exposed outdoors or subjected to controlled leaching in the laboratory. Residual insecticide has been estimated at intervals by a method involving dehydrohalogenation, and determinations have also been made of chloride content of soil, chloride leached and pH.
Results showed that both D.D.T. and benzene hexachloride were very stable in the soils, about 95 % of the former and 80 % of the latter being recoverable after 18 months. Very little chloride was leached during this period. The residual insecticide exhibited marked toxicity towards woodlice.
Eighteen months after treatment the benzene hexachloride soils prevented root growth of germinating seeds, while germination and early growth were normal in the D.D.T. soils. This harmful effect of the residual benzene hexachloride was still apparent when 1 part of the treated soil was mixed with 99 parts of the control soil (representing a concentration of less than 0–002 % of the γ-isomer).     

Effect of high boron application on boron content and growth of melons

Synthetic chelates, such as ethylene diamine tetraacetic acid (EDTA), have been shown to enhance phytoextraction of Pb from contaminated soil but also cause leaching of heavy metal-chelate complexes, posing a groundwater contamination threat. In a soil column study, we examined the effect of EDTA and a biodegradable chelate [S,S] isomere of ethylene diamine disuccinate ([S,S]-EDDS), newly introduced in phytoextraction research, on the uptake of Pb by the Chinese cabbage (Brassica rapa) and Pb leaching through the soil profile. Soil water sorption characteristics were modified by acrylamide hydrogel. The addition of 0.1 and 0.2% (w/w) of hydrogel amendments increased soil field water capacity from initial 24.6% to 28.5% and 31.3%, respectively. The additions of 2.5, 5 and 10 mmol EDTA kg^–1 soil were more effective in enhancing Pb plant uptake than comparable [S,S]-EDDS treatments, but caused (as also 10 mmol kg^–1 [S,S]-EDDS additions) unacceptably high Pb leaching in treatments with any soil water sorption conditions tested. The most efficient level of EDTA (10 mmol kg^–1) enhanced plant Pb uptake by 97 times compared to the control. Shoots Pb concentrations reached 500 mg kg^–1 of dry biomass. However, in this treatment 36.2% of total initial Pb was leached from the soil during the first four weeks after chelate addition. Hydrogel soil amendments were more effective in treatments with [S,S]-EDDS than with EDTA. In treatments with 10 mmol kg^–1[S,S]-EDDS hydrogel amended soils, plant Pb uptake was significantly reduced and Pb leach was as high as 44.2% of total initial soil Pb. At lower [S,S]-EDDS concentrations, the effect of hydrogel soil amendment on Pb leaching was the opposite. The addition of 5 mmol kg^–1 [S,S]-EDDS soil to the soil amended with 0.2% hydrogel increased Pb uptake by 18 times while only 0.2% of total initial Pb was leached. In all treatments, the concentrations of Pb in dry plant biomass were far from concentrations required for efficient soil remediation within a reasonable time span.     

酸雨对缙云山林地黄壤汞溶出的影响

Forest yellow soil and arable yellow soil in Jinyun Mountain were collected to study the effect of simulated acid rain(adjusted to pH 2.0, 3.0, 4.0 and 5.0) on the Hg leaching from soils by the methods of static extraction and dynamic leaching. The results showed that in forest yellow soils, surface accumulation of Hg occurred, and the accumulated Hg was easier to be leached out than that in arable yellow soil by acid rain. The amount of leached Hg was the largest at pH 4.0. To abate the risk of Hg pollution in water bodies by the Hg leaching from this forest soil, the Mountain should be closed, and timber-felling should be forbidden.     

Stabilization of Oxidic Tailings and Contaminated Soils by Calcium Oxyphosphate Addition: The Case of Montevecchio (Sardinia,Italy)

The effectiveness of an in situ heavy metals fixation technique aimed at converting contaminants to low solubility and low bioavail-ability forms, eliminating the risk posed by oxidic tailings and contaminated soils, was investigated. Calcium oxyphosphate salt (Ca(H₂PO₄)₂·H₂O) was used as a stabilizing agent for oxidic tailings and contaminated soils originating from Montevecchio, Sardinia, Italy. Stabilization was effected by mixing the contaminated soil or oxidic tailing sample with calcium oxyphosphate salt at various doses. The effectiveness of stabilization was evaluated by USEPA TCLP standard toxicity testing. Complementary EDTA extraction tests and biological tests using beans Phaseolous vulgaris as plant indicator were carried out. The toxicity of Pb and Cd was reduced below TCLP regulatory limits at calcium oxyphosphate doses higher than 0.7 and 0.2% w/w for soils and tailings, respectively. Lead solubility according to the EDTA test decreased with phosphate dose for both materials tested. Lead uptake by plant leaves and roots from the soil sample decreased with the phosphate addition, while Cd uptake remained almost constant. An adverse effect on plant growth and Zn uptake was observed for calcium oxyphosphate dose up to 1.1% w/w. Based on the results, a remediation scheme for oxidic tailings and contaminated soils is proposed.     

An “ex situ” microbial process for the removal of heavy metals from polluted soil: A case study of Ada rice field,Adani, Enugu State,Nigeria

An “ex situ” microbial method for the removal of heavy metals from soil is described. Elemental sulfur was added to generate the lixiviant in shaker flask experiments in which soil sampled from a polluted agricultural field was treated. The biotic oxidation of sulfur to sulfuric acid resulted in significant drop in pH of the bioleaching liquor from 6.94 to 1.8 after 50 days. In batches operated at very low (10 g/kg) sulfur concentrations, pH changed from 6.94 to 5.45. The 50 g/kg soil sulfur concentration was found to be most beneficial to the solubilization process because more than 95% of metals such as zinc (Zn), cadmium (Cd), and nickel (Ni) were recovered while approximately 67% of manganese (Mn) got solubilized. The least concentration of dissolved metals was lead (Pb) – (25%) and chromium (Cr) – (10%). Sulfate accumulation rose to 47% in samples spiked with 50 g/kg soil of sulfur. At lower sulfur concentrations, the sulfates generated were higher than the amount of sulfur added. The microbial process compared well to the abiotic process involving extraneous addition of sulfuric acid except that very high concentrations of acid had to be used. The treatment of the bioleaching wastewater promoted precipitation of the dissolved metals into insoluble hydroxides making discharge of the effluent into the environment safe. The leached soil recovered sufficiently for agricultural use after quick lime and animal manure was used to improve, stabilize, and restore its physical, chemical, and biological conditions.     

Movement of water and heavy metals (Zn, Cu, Pb and Ni) through sand and sandy loam amended with biosolids under steady-state hydrological conditions

New guidelines for using biosolids in UK agriculture favour the use of enhanced treated biosolids, such as dried and composted cakes, due to concerns about the potential for transfer of pathogens into the food chain. However, there is a need to ensure that their use is environmentally acceptable and does not increase the risk to potable water supplies or the food chain from other contaminants such as heavy metals and xenobiotic organic chemicals. The objective of this study was to determine whether the use of composted and dried mesophilic anaerobically digested dewatered (MADD) biosolids would increase the risk of heavy metal leaching from cultivated horizons when compared to more conventionally used MADD cake. Three biosolids (MADD sewage sludge cake - fresh, dried and composted) were mixed with a sand (typic quartzipsamments, %OM = 3.0, pH = 6.5) or a sandy loam (typic hapludalf, %OM = 4.8, pH = 7.6) at an application rate equivalent to 250 kg N/ha/y resulting in loadings of approximately Zn: 6 microg, Cu: 2 microg, Pb: 5 microg and Ni: 0.2 microg/g of soil dry weight basis. These amended soils were repacked into columns (0.4 m by 0.1 m internal diameter) and leaching of Zn, Cu, Pb and Ni was investigated following application of two 24 h simulated rainfall events of 4.5 mm/h. Water balance data and the use of conservative tracers (Cl- and Br ) showed that the hydrological regimes of each core were comparable and, thus, unlikely to account for differences in metal leaching observed. Although no significant difference (P = 0.05) was observed between biosolid amended and control soils, those amended with composted sludge consistently gave higher loss of all metals than did the control soils. Total losses of metals from compost amended soil over the two rainfall events were in the ranges, Zn:20.5-58.2, Cu:9.0-30.5, Pb:24.2-51.2 and Ni:16.0-39.8 microg metal/kg amended soil, compared with Zn:16.4-41.1, Cu:6.2-25.3, Pb:16.9-41.7, and Ni:3.7-25.4 microg metal/kg soil from the control soils. Losses of Zn, Cu, Pb and Ni from fresh MADD cake amended soils (19.8-41.3, 3.2-25.8, 21.6-51.6 and 7.6-36.5 microg metal/kg amended soil, respectively) and from dry MADD cake amended soils (10.7-36.7, 1.8-23.8, 21.2-51.2 and 6.8-39.2 microg metal/kg amended soil, respectively) were similar to the controls. Generally, quantities of metals leached followed the order Zn = Pb > Cu > Ni, which was consistent with the levels of metals in the original sludge/soil mixtures. These results suggest that composting or drying MADD biosolids is unlikely to increase the risk of groundwater contamination when compared to the use of MADD cake; therefore, the changes in UK sludge use in agriculture guidelines are satisfactory in this respect.     

Leaching of nitrogen from subtropical soils as affected by nitrification potential and base cations

A soil column method was used to determine the effect of nitrification on leaching of nitrate and ammonium from three acid subtropical soils after application of ammonium bicarbonate. Three soils, designated QF, GB and SU, derived from Quaternary red earth, granite and tertiary red sandstone, were collected from forest land, brush land and upland field, ranged in nitrification potential and cation exchange capacity. The results indicated that nitrate leaching increased with the soil nitrification potential. The soils with higher nitrification potential had a higher nitrate peak concentration and required a shorter time to reach it. In soils QF and GB with low cation exchange capacity, and a low content of exchangeable base cations, there were not sufficient base cations to accompany the nitrate leached with the result that ammonium and hydrogen ions were leached from the soil, and pH changes occurred in different layers of the soil column.     

Effects of soil acidification and subsequent leaching on levels of extractable nutrients in a soil

Summary The effects of soil acidification (pH values from 6.5 to 3.8), and subsequent leaching, on levels of extractable nutrients in a soil were studied in a laboratory experiment. Below pH 5.5, acidification resulted in large increases in the amounts of exchangeable Al in the soil. Simultaneously, exchangeable cations were displayed from exchange sites and Ca, Mg, K and Na in soil solution increased markedly. With increasing soil acidification, increasing amounts of cations were leached; the magnitude of leaching loss was in the same order as the cations were present in the soil: Ca²⁺>Mg²⁺>K⁺>Na⁺. Soil acidification appeared to inhibit nitrification since in the unleached soils, levels of NO ₃ ⁻ clearly declined below pH 5.5 and at the same time levels of NH ₄ ⁺ increased greatly. Significant amounts of NH ₄ ⁺ and larger amounts of NO ₃ ⁻ , were removed from the soil during leaching. Concentrations of NaHCO₃-extractable phosphate remained unchanged between pH 4.3 and 6.0 but were raised at higher and lower pH values. No leaching losses of phosphate were detected. For the unleached soils, levels of EDTA-extractable Mn and Zn increased as the soil was acidified whilst levels of extractable Fe were first decreased and then increased greatly and those for Cu were decreased slightly between pH 6.5 and 6.0 and then unaffected by further acidification. Significant leaching losses of Mn and Zn were observed at pH values below 5.5 but losses of Fe were very small and those of Cu were not detectable.