Acid Mineral Soils Research Articles

Mapping Fe-bearing hydrated sulphate minerals with short wave infrared (SWIR) spectral analysis at San Miguel mine environment, Iberian Pyrite Belt (SW Spain)

Short-wave infrared reflectance (SWIR) spectra obtained from a Portable Infrared Mineral Analyser (PIMA) were applied to map acidic mine soils at San Miguel massive sulphide deposit, Iberian Pyrite Belt, Spain. Field spectral measurements and laboratory analysis were performed on samples from 58 stations from two very polluted grounds. These analyses identified secondary and tertiary Fe-rich sulphate–hydrate minerals associated with the alteration of sulphide-bearing mine wastes and other associated infrared active minerals. The spectral absorption features for the pure salt types found in these areas allowed the preparation of a specific reference library for automatic mineral identification. Using this approach three separate zones around the sources of contamination have been discriminated: a “proximal” zone dominated by rozenite + hexahydrite, a “transitional” zone dominated by copiapite + coquimbite and a “distal” zone of hydronium–jarosite. An additional zone of “gypsum” was also recognized locally at the areas, where, last decade the neutralization of the acid soils with limestones was attempted. In addition to discriminating distinct mineralogical zones quantitative spectral data allowed contoured mineral maps to be produced that are comparable with the estimated mineralogical data obtained from conventional methods, such as XRD and field observations. These maps demonstrate that sulphate minerals were firstly formed by oxidation of the pyrite-rich ores followed by dissolution and precipitation involving a combination of oxidation, dehydration, and neutralization reactions. The study shows the potential of SWIR spectral analysis to identify and understand the distribution of efflorescent salts and other products of pyrite decomposition and provides a methodology to assist the research and monitoring of sources of environmental contamination.

Influence of soil acidity on depth gradients of microbial biomass in beech forest soils

The objectives of the study were to investigate mineral soil profiles as a living space for microbial decomposers and the relation of microbial properties to soil acidity. We estimated microbial biomass C on concentration (μg g−1 DW) as well as on volume basis (g m−2) and the microbial biomass C to soil organic C ratio along a vertical gradient from L horizon to 20 cm in the mineral soil and along a gradient of increasing acidity at five beech forest stands in Germany. Microbial biomass C concentration ranged from 17,000–34,000 μg Cmic g−1 DW in the litter layer and decreased dramatically down the profile to 29–264 μg Cmic g−1 DW at 15–20 cm depth in the mineral soil. This represents depth gradients of microbial biomass C concentrations ranging from a factor of 65 in slightly acidic and up to 875 in acidic soils. In contrast, microbial biomass C calculated on a volume basis (g Cmic m−2) showed a different pattern since a considerable part of the microbial biomass C was located in the mineral soils. In the soil profile 22–34% of the microbial biomass C was found in the mineral soil at strictly acidic sites and as much as 64–88% in slightly acidic soils. The microbial biomass C to soil organic carbon ratios decreased in general down from the L horizon in the forest floor to 0–5 cm depth in the mineral soils. In strongly acidic mineral soils however, the C to soil organic carbon ratio increased with depth, suggesting a positive relation to increasing pH. We conclude from depth gradients of soil pH and microbial biomass C to soil organic carbon ratio that pH affects this ratio at acidic sites. The inter-site comparison indicates that acidity restricts microbial biomass C in the mineral soils.

Controls on Leaching of N Species in Upland Moorland Catchments

Spatial and temporal changes in mobility of N species have been studied for three UK upland river networks, the Etherow in the South Pennines, the Nether Beck in the Lake District and the Dee in NE Scotland. The catchments are subject to N deposition at 35.1, 22.0 and 10.8–15.6 kg N ha−1 yr−1, respectively. The NH+4 leaching appears to be predominantly regulated by flow path in more polluted upland catchments. It is greatest where water draining acidified peaty soils contributes more to total discharge. Soluble organic matter may provide the dominant counter anion. In the Etherow and Dee catchments, which are dominated by acid mineral and organic soils, at high discharge NO−3 also appears to be associated with greater input of water from acidified soils. In contrast, for the Nether Beck, higher NO−3 concentrations are associated with tributaries draining soils contributing water with higher alkalinity, suggesting nitrification is important. For the Etherow and Dee, dissolved organic N (DON) appears to originate predominantly from acidified, peaty soils. Spiking experiments with peat soil from the Etherow catchment confirmed the limited capacity of these soils to utilize inorganic N inputs, favouring equilibration with NH+4 inputs and leaching losses of inorganic N throughout the year.

Aluminium-induced changes in the profiles of both organic acids and phenolic substances underlie Al tolerance in Rumex acetosa L.

The common sorrel, Rumex acetosa L. is well adapted to acid mineral soils with high availability of phytotoxic Al species. The mechanisms of Al resistance in this species are not established. Our goal was to assess the possible implications of organic acids and phenolic substances in Al detoxification in roots and shoots of this plant. R. acetosa plants were exposed in nutrient solution (pH 4.3) to a non-growth reducing Al concentration of 50 μM Al for 5 days. Exclusion of Al from root tips was visualized by haematoxylin staining. Tissue Al and Ca concentrations were analysed by ICP ES. Root and shoot concentrations of organic acids and phenolic substances were analysed by HPLC. A time-dependent (model II type) Al exclusion pattern in root tips was observed. Nonetheless, high Al concentrations accumulated in roots (1170 μg/g) and shoots (275 μg/g). Aluminium supply enhanced root citrate concentrations but decreased shoot organic acid levels. Aluminium induced high levels of anthraquinone in roots and of catechol, catechin and rutin in shoots. Aluminium resistance in R. acetosa implies both exclusion of Al from root tips and tolerance to high Al tissue concentrations. Citrate in roots and phenolics in shoots may bind Al in non-toxic form. Anthraquinones, as strong antioxidants, may play a role in a general defence response to the root stress.

Assessment of preferential flow processes in a forest-reclaimed lignitic mine soil by multicell sampling of drainage water and three tracers

Predictions of the long-term development of newly established forest-reclaimed ecosystems are required for land use planning of post-mining landscapes. The geological and mineralogical composition, the small-distance heterogeneity and inclined structures of the mine spoil's overburden sediment mixtures, as well as the physical and chemical properties of acidic and lignitic mine soil components, have raised questions about the water flow and solute transport processes in these soils. The objective of this study was to quantify preferential flow processes and spatially resolved solute transport in order to better distinguish between dominating processes for such soils. The experimental study was carried out by determining spatially resolved rates of throughfall, drainage and tracer leaching from underneath a 110 cm deep mine soil block. Drainage water was collected using 45 contiguous suction cells of 27 cm edge length. A tracer cocktail consisting of bromide, terbuthylazine, and deuterium was applied at the soil surface and subjected to natural infiltration. Tracer concentrations in drainage waters were analysed for a period of about 10 months. Then, the mine soil block was sampled completely in the form of 225 cubes of about 27 cm edge length to determine the residual bromide content. Tracer-labelled drainage in 110 cm depth occurred in spring 2001 over about 71% and in autumn 2001 over 35% of the total cross-sectional drainage area, respectively. Local drainage maxima shifted from spring to autumn, but also within drainage periods by 1–2 cell lengths. Bromide concentrations of drainage effluents varied by a factor of 4 between individual cells. Bypass-type preferential flow seems not to be a dominating transport mechanism since terbuthylazine in drainage waters occurred only singularly in spring with concentrations just above the detection limit. Perhaps the dilution in relatively large cells was too effective to detect modest contributions of tracer through preferential flow paths. Relative concentrations of deuterium and of bromide were akin during both drainage periods indicating similar transport behaviour of both tracers in the mine soil. The spatial distribution of residual bromide concentrations in the subsoil seemed to correspond with the inclined spoil ripple structures. The spatial patterns of leached bromide suggest a funnelling-type flow concentration. In this lignitic mine soil, preferential flow is presumably caused by the temporarily varying effects of multiple determinants, such as inclined dumping structures, spatial variability of hydraulic properties, water repellence, and the properties of lignitic dust and fragments with some immobile porosity.

Variation in aluminum resistance among arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal (AM) fungi mediate interactions between plants and soils, and are important where nutrient or metal concentrations limit plant growth. Variation in fungal response to edaphic conditions may influence the effectiveness of the plant-mycorrhizal association in some soil environments. Andropogon virginicus (broomsedge) colonizes disturbed sites in the eastern United States, including acidic mine soils where aluminum (Al) is phytotoxic, and Al resistance in broomsedge has been associated with colonization by the AM fungus Glomus clarum. In the present study, inter- and intra-specific variation to confer Al resistance to broomsedge was assessed among selected species of AM fungi. Broomsedge seeds were grown in sand culture inoculated with one of five isolates of three species of fungi (G. clarum, Acaulospora morrowiae, and Scutellospora heterogama). Plants were exposed to 0 or 400 microM Al in nutrient solution and harvested after 4 or 9 weeks of growth. Mean infection percentage, plant biomass, and plant tissue Al and phosphorus (P) concentrations were measured. G. clarum conferred the greatest Al resistance to broomsedge, with the lowest variability among isolates for colonization and growth inhibition by Al [tolerance indices (TI) between 22.4 and 92.7%]. Broomsedge plants colonized by A. morrowiae were consistently the most sensitive to Al, with little variation among isolates (TI between 1.6 and 12.1%). Al resistance by S. heterogama isolates was intermediate and wide-ranging (TI between 3.9 and 40.0%). Across all AM fungal isolates, resistance was associated with high rates of colonization and low tissue Al concentrations of broomsedge plants. The functional diversity in Al resistance displayed by these AM fungi reflect variation in acclimation mechanisms operating in the mycorrhizal symbiosis under environmental stress.

Starch Properties of the Sago Palm (Metroxylon sagu Rottb.) in Different Soils

We investigated the relationships between starch concentrations and activities of starch synthetic enzymes in sago palms (Metroxylon sagu Rottb.) under acid sulfate and mineral soil conditions. Plants grown naturally that had reached their maturated stage were sampled. We found that the growth in acid sulfate soil is lower than that in mineral soil and that starch granules were larger and there was more amylase activity in acid sulfate soil than in mineral soil. Lower amylase activity in mineral soil could eliminate the degradation of starch, making the smaller granules suitable for storing large amounts of starch in a limited space inside cells.

Acid neutralising capacity of two different bauxite residues (red mud) and their potential applications for treating acid sulfate water and soils

The acid neutralising capacity (ANC) and potential beneficial uses of 2 different bauxite residues (red mud) were investigated. The results show that the ANC is much higher in the red mud disposed of using a dry stacking method at the Pingguo Alumina Refinery (China) than in the red mud disposed of by a wet method using seawater at the Queensland Alumina Ltd Refinery (Australia). The higher ANC in the Pingguo red mud is attributable to its high CaO and low SiO2. An incubation experiment showed that leaching of alkaline materials from the lime-treated sample was much greater than that from the red mud-treated sample. This suggests that red mud may be superior to lime for treating potential acid sulfate soils, which contain sulfide minerals that could take a long time to oxidise and release soluble acid. The effects of 2 acid-filtering systems were tested, both of which used red mud as the main material for removal of acid from passing acidic water. The results showed that the red mud–CaCO3 filter performed better than the red mud–Mg(OH)2 filter. Results from pot trials in Australia further demonstrated that the application of combined red mud and sewage sludge significantly improved the soil conditions for the growth of 5 Australian native tree species, in addition to Eucalyptus paniculata, which successfully grew in the same mine soil amended with the red mud and sewage sludge in previous work of G. Maddocks et al. The results from the pot experiment in China showed that the application of combined neutralising agents (red mud/lime blends) and sewage sludge to the extremely acidic mine soil was insufficient for creating appropriate ecological conditions for the growth of vetiver grass. In this experiment, additional application of zeolitic rock powder significantly improved the growth performance of the plant.

Dinitrogen and Nitrous Oxide Formation in Beech Forest Floor and Mineral Soils

A 15N tracer study was conducted to determine N2 and N2O fluxes and the processes responsible for the formation of N2O in two beech (Fagus silvatica L.) forest soils: an acid mineral soil (AM) (pH = 3.8) and the overlying acid forest floor (AFF) (pH = 3.8) from the Solling and a less acid mineral soil (LAM) (pH = 5.2) from the Göttinger Wald. Ammonium and nitrate of undisturbed soil cores were labeled by injecting 15N. The evolved gases, N2O and N2, and the ammonium and nitrate concentrations in the soils were measured together with the 15N abundances over a period of 8 d. Nitrous Oxide was produced in all soils by denitrification. Nitrate was reduced to N2 at higher soil pH (LAM) and in the AFF. The end product of denitrification at the lower soil pH (AM) was N2O. The N2O and N2 emission calculated on an areal basis decreased from LAM, AFF, to AM. The N2O/(N2O + N2) ratios decreased from AM (1.0), AFF (0.97), to LAM (0.80) during the initial period indicating that the main product of denitrification was N2O. On prolonged incubation the N2O/(N2O + N2) ratios decreased for AFF and LAM to 0.78 and 0.32, respectively, and was attributed to a gradual decrease in nitrate concentration. We estimate the in situ N2 emissions to be 0.71 and 0.51 kg N ha−1 yr−1 for the Göttinger Wald and the Solling, using published annual in situ N2O emissions and our N2/N2O ratios. The in situ N2O emissions of the Göttinger Wald and Solling are 0.17 and 3 kg ha−1 yr−1 and the N2 emissions increased the annual denitrification losses to about 0.88 and 3.51 kg ha−1 yr−1 The approach for estimating in situ N2 emissions has to be improved in future studies.

Nitrous oxide emission as affected by liming an acidic mineral soil used for arable agriculture

The effect of liming an acidic mineral soil (Dystric Nitosol from southern China), used for arable agriculture, on N2O emission was studied in an incubation experiment. After the soil pH had been raised from pH 4.4 to 5.2, 6.7 and 8.1, soil samples were either amended with NH4+ and incubated aerobically, favoring nitrification or, after application of NO3−, the incubation took place under anaerobic conditions, favoring denitrification. Gas sampling for N2O determination and soil analyses were performed at regular intervals up to 13 days. Under nitrification conditions only small N2O emission rates were observed (max. 6 μg N kg−1 d−1) with significant differences between high and low pH values during the first 2 days of incubation. The nitrifying activity was low, even with high pH, and this, together with good aeration conditions, could partly explain the small N2O evolution. During denitrification, however, cumulative N2O emissions reached much higher values (1600 μg N kg−1 in comparison to 40 μg N kg−1 under nitrification conditions). N2O emission during denitrification was significantly enhanced by increasing soil pH. Under alkaline conditions (pH 8.1) a large nitrite accumulation occurred, which was in line with the highest nitrate reductase activity determined in this treatment. The limited availability of organic carbon is probably the main reason for the absence of further reduction of NO2− to N2O or N2. At pH 6.7 the total N2O emission was slightly higher than at pH 8.1, although the start of pronounced emissions was retarded and only small amounts of NO2− accumulated. Acid soil conditions caused either negligible (pH 4.4) or only small (pH 5.2) N2O emissions. It can be concluded that these kinds of soil, used alternatively for production of upland crops or paddy rice, are prone to high N2O emissions after flooding, particularly under neutral to alkaline conditions. In order to avoid major N2O evolution and accumulation of nitrite, which can be leached into groundwater, the pH should not be raised to values above 5.5–6.

Iron sulfide oxidation as influenced by calcium carbonate application.

Two overburden materials, with different FeS2 contents (1.9 and 4.1%) and low acid neutralization potential, were limed with CaCO3 at rates of 0, 25, 50, 75, 100, and 125% based on the amount of CaCO3 needed to provide an acid-base account deficit (A/Ba) of zero (A/Ba = neutralization potential--potential acidity--exchangeable acidity). The limed overburden materials were inoculated with Thiobacillus ferrooxidans and leached weekly with deionized water. Residual FeS2 and CaCO3 were determined in samples over a 378-d period. Oxidation followed zero-order kinetics with respect to FeS2 concentration at pH values greater than 4 and first-order kinetics at pH values less than 4. Zero-order oxidation rates ranged from 0.01 to 0.46 micromol g(-1) d(-1) in the overburden with 1.9% FeS2 and from 0.01 to 0.22 micromol g(-1) d(-1) in the overburden with 4.1% FeS2. Oxidation following the first-order rate law had a first-order rate constant of 0.03 d(-1) in the 1.9% FeS2 overburden and 0.01 d(-1) in the 4.1% FeS2 overburden. The calculated half-life was 23 d for the 1.9% FeS2 overburden and 69 d for the 4.1% FeS2 overburden. Additions of CaCO3 affected FeS2 oxidation by controlling the pH of the system. Liming to greater than 50% of the acid-base account deficit did not significantly affect the zero-order oxidation rate. Dissolution of the applied CaCO3 was found to be faster than the oxidation of FeS2 at pH values greater than 4. It was projected that at lime rates up to 125%, the CaCO3 would dissolve and leach out of the system before all the FeS2 oxidized, leaving the potential for acid minesoil formation.

Peranan Mikoriza VA, Rhizobium dan Asam Humat pada Pertumbuhan dan Kadar Hara Beberapa Spesies Legum Penutup Tanah

The utilization of acid mineral soil often faces the problem of Al toxicity and low available P. The efforts to improve root function and neutralize the effect of high available Al are becoming important for increasing the growth of legumes, particularly as the cover crops at the plantation on acid soil. This research was aimed to find the effect of VA mycorrhyza inoculation, rhizobium, and humic acid on the growth and nutrient content of four different legume species. It was a three factor factorial experiment arranged in a completely randomized design with three replications. The first factor was four legume species: Calopogonium mucunoides, CaloPogonium ceurelieum, Centrosema pubescens and Puerari iavanica the second factor was four different inoculants: none (M0), MVA (M1), rhizobium (Mz), MVA + rhizobium (M3); the third factor was two rates of humic acid application: without (Ho) and with humic acid (H1) The results proved the positive effect of those three factors on the growth of shoot and roots. The responses of root growth on microorganism inoculations and humic acid were different among the legume cover crop species. The role of humic acid was significantly better if there was a synergism between MV A and rhizobium. Key words: Mycorrhyza, Rhizobium, Humic acid, Legume cover crop

Effects of liming and fertilization (N, PK) on stem growth, crown transparency, and needle element concentrations of Picea abies stands in southwestern Sweden

Liming and (or) application of specific nutrients have been proposed as countermeasures to the acidification of forest soils in southern Sweden. The aim of this study was to investigate whether stem growth, crown transparency, and needle element concentrations of Picea abies (L.) Karst. growing on acidic mineral soils in southwestern Sweden are affected by additions of lime, lime plus P and K, or N in low doses (treatments: CaPK, Ca, N, CaPKN, and 2Ca2P2K). During the 5-year observation period following treatment with CaPKN there was a tendency to increased stem growth (possibly overestimated). The most plausible cause of this growth response was increased N availability in the soil, although the possibility that there was a minor effect of the PK application could not be excluded. None of the treatments affected the crown transparency. Several significant changes in elemental concentrations of current-year needles were associated with the treatments. The control plots in the experimental stands showed no severe damage or nutrient deficiencies despite the relatively acidic soils. These findings, together with the small treatment effects, suggest that there is no acute need for liming and (or) PK addition in P. abies stands on similar sites in southwestern Sweden.

Soil cations influence bryophyte susceptibility to bisulfite.

The hypothesis that metal ions absorbed by bryophytes from the underlying soil may ameliorate adverse effects of SO2 was investigated in the terricolous moss species Pleurozium schreberi (Brid.) Mitt. and Rhytidiadelphus triquetrus (Hedw.) Warnst. Dilute sodium bisulfite solutions (equivalent to dissolved SO2) were applied to shoots isolated from soil or in contact with artificial substrata. Marked inhibition of net photosynthesis was observed within 2 h of treatment with 0.3 mM bisulfite in both mosses. Progressive recovery of net photosynthesis occurred 2-8 h after bisulfite treatment, although the extent of this depended on the concentration and pH of the solution. When R. triquetrus and P. schreberi were grown on artificial substrata (calcareous, acid-mineral or acid-organic) with weekly bisulfite applications, the only significant effect was poorer growth of P. schreberi receiving bisulfite on the calcareous and acid-organic substrata. In both species, growth on the calcareous substratum led to increased concentrations of exchangeable Ca2+, whereas exchangeable Fe3+ concentrations increased following growth on the acid-mineral soil. In another experiment the two mosses were pre-treated with either Ca2+ or Fe3+ before incubation with bisulfite. In P. schreberi, the depression of net photosynthetic rate caused by bisulfite was ameliorated from 33 to 64% of the control by pre-treatment with Fe3+, but it was unaffected by Ca2+ pre-treatment. In R. triquetrus, the amelioration caused by Fe3+ pre-treatment was from 16 to 60% of the control, but pre-treatment with Ca2+ gave a greater amelioration, to 75% of the control value. The responses are discussed in terms of soil preferences of the mosses and possible underlying bisulfite amelioration mechanisms.

Evaluation of Mehlich-1 and Mehlich-3 extraction procedures for plant nutrients in acid mineral soils of Florida*1

Increasing number of soil testing laboratories in the mid-Atlantic and southeastern states of the United States are adopting Mehlich-3 (M-3) as the official extraction procedure in place of Mehlich-1 (M-1) or the dilute double acid method. Several studies have indicated that the M-3 has at least equivalent if not better extractability, particularly of micronutrients in the acidic and mineral soils in these regions. The objective of this study was to determine the correlation between the two Mehlich procedures and to provide conversion equations from M-1 to M-3 procedure. This is expected to serve as an estimate of nutrient availabilities particularly by the extension personnel and crop professionals evaluating different test procedures. A set of 519 mineral soil samples received at the UF/IFAS Extension Soil Testing Laboratory were selected and assayed with both M-1 and M-3 extracting solutions. The concentrations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), zinc (Zn), manganese (Mn), and boron (B) in the extracted solutions were determined and comparative equations were developed. Highly significant linear correlation coefficients were found for all the nutrients extracted with both M-3 and M-1. Acidic to near neutral soil pH range of the soils had no influence on the efficiencies of extraction solutions. The equations developed showed that P, Cu, Mn, and B extracted were 47%, 94%, 101%, and 111% more with M-3 than with M-1 while for K, Mg, and Zn generally remained the same for both methods. *This work was supported in part by Caisse Nationale de l'Assurance Maladie des Travailleurs Salariés—Institut National de la Santé et de la Recherche Médicale (CNAMTS INSERM) grant no. 3 AM 055 Paris, France, Association pour la Recherche sur le Temps Biologique (A.R.T.B.C.), Villejuif, France, and Compagnie de Développement Aguettant, Lyon, France.

Land application of alum sludge from water purification plant to acid mineral soil treated with acidic water

Land application of alum sludge has been considered to be an economical disposal method. However, its negative effects on the environment have been a cause for concern. In one example, an acid soil was treated with alum sludge from a water purification plant at 0 to 18% rate. Indian mustard was grown on the treated soil in a greenhouse for 5 weeks, and irrigated with pH 4 water during growth. Changes in the soil properties, leachate chemistry, plant growth, and plant uptake of elements by the sludge treatment were determined. The sludge treatment increased the buffer capacity to acidity, hydraulic conductivity, water-holding capacity, and phosphate adsorption of the soil and decreased the bulk density and mobility of small particles. The sludge treatment reduced the leaching of Al, Mg, K, Na, and Mn but increased leaching of Ca. The sludge treatment also increased the amount of biomass and enhanced root elongation. The plant absorbed a lower amount of cations and P, but a larger amount of Ca with the sludge treatment.

Amelioration of nickel phytotoxicity in muck and mineral soils.

In situ remediation (phytostabilization) is a cost-effective solution for restoring the productivity of metal-contaminated soils and protection of food chains. A pot experiment with wheat (Triticum aestivum L.), oat (Avena sativa L.), and redbeet (Beta vulgaris L.) was conducted to test the ability of limestone and hydrous ferric oxide (HFO) to ameliorate Ni phytotoxicity in two soils contaminated by particulate emissions from a nickel refinery. Quarry muck (Terric Haplohemist; 72% organic matter) contained 2210 mg kg(-1) of total Ni. The mineral soil, Welland silt loam (Typic Epiaquoll), was more contaminated (2930 mg Ni kg(-1)). Both soils were very strongly acidic, allowing the soil Ni to be soluble and phytotoxic. Nickel phytotoxicity of the untreated muck soil was not very pronounced and could be easily confused with symptoms of Mn deficiency that occurred in this soil even with Mn fertilization. Severe nickel phytotoxicity of the untreated mineral soil prevented any growth of redbeet, the most sensitive crop; even wheat, a relatively Ni-resistant species, was severely damaged. White banding indicative of Ni phytotoxicity was present on oat and wheat leaves grown on the acidic mineral soil. Soil Ni extracted with diethylenetriaminepentaacetic acid (DTPA) and 0.01 M Sr(NO3)2 was indicative of the ameliorative effect of amendments and correlated well with Ni concentrations in plant shoots. Making soils calcareous was an effective treatment to reduce plant-available Ni and remediate Ni phytotoxicity of these soils to all crops tested. The ameliorative effect of HFO was crop-specific and much less pronounced.

Why plants grow poorly on very acid soils: are ecologists missing the obvious?

Factors associated with soil acidity are considered to be limiting for plants in many parts of the world. This work was undertaken to investigate the role of the toxicity of hydrogen (H(+)) which seems to have been underconsidered by ecologists as an explanation of the reduced plant growth observed in very acid soils. Racial differences are reported in plant growth response to increasing acidity in the grass Holcus lanatus L. (Yorkshire-fog) and the tree Betula pendula Roth (Silver Birch). Soils and seeds were collected from four Scottish sites which covered a range of soils from acid (organic and mineral) to more base-rich. The sites and their pH (1:2.5 fresh soil:0.01 M CaCl(2)) were: Flanders Moss (FM), pH 3.2+/-0.03; Kippenrait Glen (KP), pH 4.8+/- 0.05; Kinloch Rannoch (KR), pH 6.1+/-0.16; and Sheriffmuir (SMM), pH 4.3+/-0.11. The growth rates of two races of H. lanatus, FM and KP, and three races of B. pendula (SMM, KP and KR) were measured in nutrient solution cultures at pH 2.0 (H. lanatus only), 3.0, 4.0, 5.0, and 5.6. Results showed races from acid organic soils (FM) were H(+)-tolerant while those from acid mineral soils (SMM) were Al(3+)-tolerant but not necessarily H(+)-tolerant. These results confirmed that populations were separately adapted to H(+) or Al(3+) toxicity and this was dependent upon the soil characteristics at their site of collection. The fact of plant adaptation to H(+) toxicity supports the view that this is an important factor in very acid soils.

Interaction of lime, organic matter and fertilizer on growth and uptake of arsenic and mercury by Zorro fescue (Vulpia myuros L.)

The Sulphur Bank Mercury Mine (SBMM) is an abandoned open pit mine located on the eastern shores of Clear Lake, California. Revegetation efforts have been difficult because the mine-soils at SBMM have low pH, low fertility and elevated As and Hg concentrations. In a greenhouse study, we examined the interactions of lime, N, P and OM additions with respect to plant growth, and As and Hg uptake. Three selected acidic mine-soils from the site containing high (164 mg/kg) (S-H), medium (123 mg/kg) (S-M) and low (31 mg/kg) (S-L) total As content were planted to the Eurasian annual grass, Zorro fescue (Vulpia myuros L.). The Hg concentrations for these soils varied between 1700 and 3000 mg/kg with S-L > S-H ≅ S-M. A factorial design used 3 soils, 2 lime, 2 N, 2 P and 2 OM treatments with treatments replicated three times. Multiple regression analyses indicated a strong relationship between As plant uptake, root length density (RLD) and soluble As. A highly significant linear relationship between Hg uptake and RLD for plants growing on the three soils illustrated the importance of plant root characteristics in influencing Hg uptake. Soluble As decreased in the order S-H > S-M > S-L in positive correlation with P and DOC but in inverse relationship to oxalate extractable Fe. Lime and OM additions correlated negatively with soluble Hg and Hg tissue concentration due to either Hg adsorption to OM or to inorganic surfaces. Addition of lime increased dry matter yield and Hg uptake in all three soils.

Solubility of lead, zinc and copper added to mineral soils

Elevated levels of heavy metals in soils are a result of industrial activities, atmospheric deposition, and the land application of sewage sludges and industrial by-products. Their persistence in the soil environment has created interest in the possible changes in solubility. In this study, total dissolved concentrations of Pb, Zn, and Cu were monitored in seven metal-amended soils (a calcareous and six acid mineral soils). Single metal solutions were added to soils and equilibrated (aged) for 40 days. During the 40 days the soil was allowed to air-dry and was rewetted in cycles of about 5 days. At the end of this reaction period, metal solubility was measured (by atomic absorption spectrometry and direct current plasma spectrometry) at the initial soil pH and at decreased pH values which were induced by addition of small aliquots of acid. As expected, solubility of added Pb, Zn, and Cu increased with a decrease in pH. Furthermore, the results showed that the solubility relationship with pH was similar in all non-calcareous soils. This suggests that metal solubility may be controlled by similar soil components, presumably involving soil characteristics such as pH, organic matter content, and soil mineralogy. For each metal, an approximate pH value was found at which solubility deviated from the solubility of metals when they occur in soils at typical (natural) values. This pH was about (pH±0.2): 5.2 for Pb, 6.2 for Zn, and 5.5 for Cu. Thus, pH values below these thresholds may enhance metal mobility, biological availability and toxicity in soils. Metals dissolved at higher pH in the calcareous soil (18.8 g kg −1 inorganic carbon, initial pH 8.2). In a calcareous soil, a significant fraction of these metals react with carbonates, and decreased pH results in much higher metal dissolution. Yet, metal solubility in soils is not determined by the formation and dissolution of single metal compounds.