Soil Solution pH Values Research Articles

Eficiência do fosfato natural para o arroz irrigado em solo do sul do Brasil

Com o objetivo de avaliar a eficiência do fosfato natural na cultura do arroz irrigado, foi desenvolvido um experimento onde testou-se: a) fontes de fósforo(P) : 1- Superfosfato triplo (SFT); 2- Fosfato natural (FN); e b) Doses de P: 0, 10, 20, 40 e 80 mg kg-1. Arroz da cultivar EMBRAPA 7 "TAIM", foram cultivadas em vasos durante trinta dias. O pH na solução do solo não diferiu entre as doses na mesma fonte. O P na solução aumentou com o acréscimo das doses de P, porém na primeira coleta não diferiu entre as fontes. Na segunda coleta os teores de P foram similares nas diferentes doses para a mesma fonte, diferindo apenas no SFT na dose de 80 mg kg-1. A produção de matéria seca aumentou conforme a dose de P sendo que a dose de 80 mg kg-1 foi superior nas duas fontes. Os teores de P na solução do solo e na planta, a quantidade acumulada de P e a produção de matéria seca do arroz, aumentaram com o acréscimo das doses de P aplicadas ao solo; o fosfato natural apresentou alta eficiência agronômica a partir de doses equivalentes à 40 mg kg-1 de P.

Bromide Adsorption by Reference Minerals and Soils

Bromide, Br−, adsorption behavior was investigated on amorphous Al and Fe oxide, montmorillonite, kaolinite, and temperate and tropical soils. Bromide adsorption decreased with increasing solution pH with minimal adsorption occurring above pH 7. Bromide adsorption was higher for amorphous oxides than for clay minerals. Shifts in point of zero charge (PZC) were observed on amorphous Al and Fe oxide following Br− adsorption, suggesting an inner‐sphere adsorption mechanism for Br− on these surfaces. Ionic strength effects indicated an inner‐sphere adsorption mechanism for Br− on kaolinite and an outer‐sphere adsorption mechanism on amorphous Fe oxide. Two chemical surface complexation models, the constant capacitance model and the triple layer model, were able to describe Br− adsorption as a function of solution pH on all materials. For the oxides and clay minerals and most of the soils the fit of the constant capacitance model, containing an inner‐sphere adsorption mechanism, was improved over that of the triple layer model, containing an outer‐sphere adsorption mechanism, as measured by the overall variance, VY Bromide adsorption on amorphous Fe oxide as a function of solution pH and solution ionic strength was well described using the triple layer model. Our results indicate that Br− would most likely not act as a conservative tracer at soil solution pH values below 7. Therefore, we suggest that researchers carefully evaluate the pH regime and mineralogy of their study site before assuming that Br− can be applied as a conservative tracer for transport experiments.

The impact of sampling techniques on soil pore water carbon measurements of an Icelandic Histic Andosol

The carbon in soil pore water from a Histic Andosol from Western Iceland was studied at three different scales; in the field, in undisturbed outdoor mesocosms and in laboratory repacked microcosms. Pore water was extracted using suction cup lysimeters and hollow-fibre tube sampler devices (Rhizon samplers). There were significant differences in all measured variables, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and pH values between the scales of the experiment. Gaseous constituents of soil solution and pH were more susceptible to changes in scale and the type of sampling devices used. Dissolved inorganic carbon concentrations did not differ significantly between field and mesocosm solutions but where up to 14 times lower in microcosms compared to mesocosms solutions. Rhizon samplers yielded solutions with up to 4.7 times higher DIC concentrations than porous cup lysimeters. Mesocosm surface horizon DOC concentrations were 20 and 2 times higher than in field and microcosms respectively. There was difference in DOC concentration between sampling methods (up to 8 times higher in suction cups than rhizon samplers) above 50 cm depth. Soil solution pH values did not differ between field and mesocosms and mesocosms and microcosms respectively down to 80 cm depth. Direct comparison between field and microcosms was not possible due to the nature of sampling devices. Soil solutions sampled with Rhizon samplers yielded lower pH values (up to 1.3 pH units) than those sampled with suction cups. Twenty percent of annually bound organic carbon at the soils surface under field conditions was lost by leaching of DOC and through decomposition to DIC in disturbed non-vegetated microcosms. This percentage increased to 38% in undisturbed vegetated mesocosms highlighting the importance of surface vegetation in importing carbon to soils. Increased influx of nutrients will increase growth and photosynthesis but decrease carbon sequestration in near surface horizons. Although field studies considering long-term anthropogenic changes in pedogenesis require considerable experimental duration, more rapid experiments can be conducted with confidence in micro- and mesocosms as in this research.

Acidification of freshwaters by red soil in a subtropical silicate rock area, Okinawa, Japan

Two samples of red soil, one from Gushikawa Recreation Center (GRC) and one from Okinawa Royal Golf Club (ORGC), were examined for particle size distribution, textures, minerals, and chemical compositions. The effects of particle size and grinding of clay minerals on pH, electrical conductivity (EC), and dissolved chemical species were studied in deionized water and river water. The results of red soil solutions were compared with those of acidic waters found in red soil dominated areas. The minimum pH values of soil solutions extracted by deionized water were 4.38–5.36 and 5.16–5.89 and the maximum values of EC were 4.91–16.98 mSm−1 and 3.54–11.23 mSm−1 for GRC and ORGC, respectively. In the river water samples equilibrated with red soils, the minimum pH values were 4.48–5.10 and 4.77–5.91 and the maximum EC values were 19.6–34.2 mSm−1 and 17.5–25.0 mSm−1 for GRC and ORGC, respectively. The values of pH and EC varied with the soil–solution ratio and the particle size. The chemical composition of river water without mixing with red soil shows Na+≫K+ and Ca2+≫Mg2+. After mixing with red soil, the trend of the concentrations changed to Na+≫K+ and Mg2+≫Ca2+, which is the same as that of soil solutions in deionized water as well as that of acidic waters found in the red soil area. The pH of the acidic waters was 4.95–5.81 and EC was 7.76–30.0 mSm−1. Laboratory experimental results agreed well with those found in the field in terms of trend of concentrations of the chemical species and pH. Therefore, the results of this study suggest that the low pH and trend of the concentrations of chemical species of the acidic waters found in the red soil dominated areas were the result of the interaction of natural water and red soil.

EFFECTS OF THE ST. LUCIE ESTUARY MUCK SEDIMENT APPLICATION ON METAL SOLUBILITY AND pH OF SANDY SOILS: A LABORATORY OBSERVATION 1

Heavy metal contamination from the beneficial re-use of muck sediment in agriculture is a cause for concern. Information is needed about the leachability of metals from land-applied muck sediment and the effects of muck sediment application on soil properties. For this purpose, the water solubility of metals from muck sediments at various pH values and the effects of muck sediment application on metal leachability and pH values of sandy soils were determined by leaching soil samples amended with different rates of muck sediments. The leachates and soil solutions extracted from the muck-amended soils were analyzed for pH, electrical conductivity (EC), and concentrations of heavy metals (Cd, Cr, Cu, Co, Ni, Pb, and Zn). Rapid increases in solubility of heavy metals from the muck at pH levels below 6.0 suggest that muck sediments may be most suitable for application to slightly acid to slightly alkaline soils. Soil solution pH values from soils amended with muck sediments increased with increasing muck rates. Electrical conductivity of soil solution in the muck-amended soils was higher than in soils without muck amendment. The EC values increased with increasing muck rates. Application of muck sediment increased the concentrations of Cd, Co, Ni, and Pb, and decreased the concentrations of Cu and Zn in soil solution. However, the concentrations of Cd (<40 μg L−1), Co (<44 μg L−1), Cr (<30 μg L−1), Cu (<105 μg L−1), Ni (<84 μg L−1), Pb (<128 μg L−1), and Zn (<134 μg L−1) were generally low in the soil solution from muck-amended soils. The salts in muck sediments were easily removed from the amended soils by leaching, suggesting that the added salts from muck sediments may not have long-term effects on plant growth. Relatively high EC values in the first leachates from the muck-amended soils were observed, especially for soils amended with muck at a high rate. However, application of increasing amounts of muck sediments increased soil pH. The pH increased with increasing muck rates, and was correlated positively with Na/Ca, Na, K, Na/(Ca+Mg+K), and Na/(Ca+Mg+K+Na) in the leachates and water soluble Na/Ca, Na, Na/(Ca+Mg+K), and Na/(Ca+Mg+K+Na) in the muck sediments; it was negatively correlated with Ca in leachates and water soluble Ca in the muck sediments. These results suggest that application of muck sediments does not result in a marked change in soil pH at low rates.

Role of pH in partitioning and cation exchange of aromatic amines on water-saturated soils

Predicting the reversible interactions between aromatic amines and soil is essential for assessing the mobility, bioavailability and exposure from contaminated sites. Reversible sorption mechanisms of aniline and α-naphthylamine were investigated by using single and binary solute sorption to five soils at several pH values, and by applying a distributed parameter (DP) model. The DP model assumes linear partitioning of the neutral species into soil organic matter domains and organic cation binding on negative-charged sites with the exchange coefficients represented by a Gaussian probability distribution. Sorption nonlinearity was attributed to cation exchange with varying site affinities, which was adequately simulated using the DP model. Greater uptake by hydrophobic partitioning and selectivity for cation exchange sites was observed for α-naphthylamine compared to aniline. Sorption of α-naphthylamine was not impacted quantitatively by aniline under those conditions examined; however, aniline sorption was reduced by α-naphthylamine with the largest reduction occurring in the soil with the lowest pH. DP model simulations showed that although hydrophobic partitioning increases with soil–solution pH, cation exchange still contributes significantly to the total sorption even at soil–solution pH values greater than p K a+2.

Acidification of Red Pine Forest Soil Due to Acidic Deposition in Chunchon, Korea

The effect of acidic deposition on the soil under red pine forest in Chunchon, Korea was investigated. Precipitation, stream water, and soil solution chemistry were monitored at the watershed from 1997 to 1998. Acidity of the open-bulk precipitation was often neutralized by large amounts of ammonia (NH3) that might have originated from livestock farming and fertilization. Estimated elemental budget at the watershed showed a positive correlation between loss of base cations and proton (H+) production due to nitrogen transformation in soil (ΔH+NT: ([NH4+]in-[NH4+]out)- ([NO3−]in-[NO3−]out)). When ΔH+NT increased, concentrations of nitrate in soil solutions also increased. Consequently, pH values of soil solutions decreased, although ion exchange with base cations contributed to buffer reaction. Since acid buffering capacity of the red pine forest soil was small, it was concluded that the input of ammonium nitrogen enhanced nitrification in soil thus causing soil acidification represented by loss of base cations from the watershed.

Relationships among foliar chemistry, foliar polyamines, and soil chemistry in red spruce trees growing across the northeastern United States

Forest trees are constantly exposed to various types of natural and anthropogenic stressors. A major long-term goal of our research is to develop a set of early physiological and biochemical markers of stress in trees before the appearance of visual symptoms. Six red spruce (t Picea rubens Sarg.) stands from the northeastern United States were selected for collection of soil and foliage samples. All of the chosen sites had soil solution pH values below 4.0 in the Oa horizon but varied in their geochemistry. Some of these sites were apparently under some form of environmental stress as indicated by a large number of dead and dying red spruce trees. Samples of soil and needles (from apparently healthy red spruce trees) were collected from these sites four times during a two-year period. The needles were analyzed for perchloric acid-soluble polyamines and exchangeable inorganic ions. Soil and soil solution samples from the Oa and B horizons were analyzed for their exchange chemistry. The data showed a strong positive correlation between Ca and Mg concentrations in the needles and in the Oa horizon of the soil. However, needles from trees growing on relatively Ca-rich soils with a low exchangeable Al concentration and a low Al:Ca soil solution ratio had significantly lower concentrations of putrescine and spermidine than those growing on Ca-poor soils with a high exchangeable Al concentration and a high Al:Ca soil solution in the Oa horizon. The magnitude of this change was several fold higher for putrescine concentrations than for spermidine concentrations. Neither putrescine nor spermidine were correlated with soil solution Ca, Mg, and Al concentrations in the B horizon. The putrescine concentrations of the needles always correlated significantly with exchangeable Al (r2=0.73, t p≤0.05) and soil solution Al:Ca ratios (r2=0.91, t p≤0.01) of the Oa horizon. This suggests that in conjunction with soil chemistry, putrescine and/or spermidine may be used as a potential early indicator of Al stress before the appearance of visual symptoms in red spruce trees.

Sorption of cupric, dichromate and arsenate ions in some New Zealand soilds

Concentrated solutions of copper (Cu2+), dichromate (Cr2O2−7) and aresenate (AsO43−) ions (CCA solutions) are used extensively in the New Zealand timber preservation industry. These ions are therefore, potential soil pollutants at timber treatment sites. Sorption of these three ions was examined by the surface and sub-surface horizons of two free-draining New Zealand soils over a range of soil solution pH values.

PH influence on selectivity and retention of heavy metals in some clay soils

The problem of varying species of heavy metals existing as individual species or in combination with each other in simulated contaminant leachates (solutions) is studied in relation to selectivity and retention in four different kinds of soil. The influence of pH on the retention characteristics is also examined. The results obtained from the heavy metals single-species and composite-species adsorption tests indicate that in evaluating the attenuation potential of the soil substrate (i.e., contaminant attenuation), account needs to be given to the sensitivity of the soil – heavy metals contaminant system to the pH of the leachate and the competitive effect between the heavy metals present in the leachate. A change in the soil solution pH results in a corresponding change of the dominant retention mechanism of heavy metals in the soils. At high pH values, precipitation mechanisms (e.g., precipitating as hydroxides and (or) as carbonates) dominate. As pH decreases, precipitation becomes less important, and cation exchange becomes dominant. High amounts of heavy metals are retained in the soils if the soil buffer capacity remains high enough to resist a change in pH. The selectivity order of heavy-metal retention in soils depends on the pH of soil solution. At soil solution pH values above 4 or 5, when precipitation prevails, the selectivity order obtained is given as Pb &gt; Cu &gt; Zn ≥ Cd, as demonstrated for the illite, montmorillonite, and natural clay soils. At lower soil solution pH values, the selectivity order obtained is given as Pb &gt; Cd &gt; Zn &gt; Cu, as can be seen in the case of kaolinite and montmorillonite. Key words : heavy metals, retention, selectivity, preferential adsorption, precipitation.

Selective sequential extraction analysis of heavy-metal retention in soil

The selective sequential extraction method of analysis is used in this study to determine the distribution of heavy metals in some clay soils, to assist in evaluation of the role of the various clay soil solids (clay minerals, organics, amorphous materials, and carbonates) in heavy-metal retention capability as a function of acidity of the leachate. The chemical speciation model MINTEQ (metal speciation equilibrium model for surface and groundwater) is used to calculate the probable percent distribution of different species of heavy metals present in the leachate used. The selective sequential extraction method is based on the fact that different forms of heavy metals that are retained in soil (e.g., as oxides, hydroxides, carbonates, bound with organic matter) can be extracted selectively by using appropriate reagents. The results show that heavy metals can be retained in the four clay soils studied by several soil phases or mechanisms such as exchangeable, carbonate, hydroxide, and organic phases. The retention of heavy metals in any phase depends on soil solution pH, soil constituents, and the type of heavy metal. At high soil solution pH values, retention of heavy metal by precipitation mechanisms prevails, whereas at low soil solution pH, retention by cation exchange mechanisms becomes dominant. The results from the selective sequential extraction analysis support the conclusion of the significance of soil buffer capacity with regard to heavy-metal retention. The capacity of the soils to retain high amounts of heavy metals as they receive increasing amounts of acid (i.e., as the pH is reduced) depends directly on the soil initial pH values and on their buffer capacities. Key words : selective sequential analysis, exchangeable cations, heavy metals, equilibrium models, oxides.