The role of calcium in buffering soils

Abstract. Calcium is the soluble cation that occurs in largest amount in most soils. It does not take part directly in the proton transfer reactions involved in pH-buffering, but it provides the cation charge balance for these reactions. It is also the complementary cation in formulations of chemical potential for many other ions in soils. The presence of free calcium carbonate in calcareous soils. The presence of free calcium carbonate in calcareous soils ensures a very high soil buffer capacity; d AB/ d pH ≃ 1000 Eq. m⁻³.
In acid mineral soils, dissolution and precipitation of aluminium ions contribute to the buffering processes, but most of the buffering in non-calcareous soils is caused by specific ion adsorption at variable-charge sites, in particular those associated with the dissociation of humus acids. Typical buffer capacity values of non-calcareous soils vary from 10 Eq. m⁻³ for sandy soils to 100 Eq. m⁻³ for peats. The pH changes associated with buffering are produced by leaching of calcium from soil, or by adding calcium to soil in liming materials.     

The effect of regeneration burning upon the nutrient status of soil in two forest types in southern Tasmania

In two forest types in southern Tasmania, eucalypt rainforest (mixed forest) and eucalypt dry sclerophyll forest, surface soils (0–10 cm) from stands that had been clear-felled and burned between 1976 and 1979 were compared with those from uncut, unburned stands. Factors compared were total organic C, N, P, K, Mg, Ca, Zn, Mn; pH; exchangeable Ca, Mg, and K; cation exchange capacity; extractable P; soil phosphate buffering capacity; and N-mineralisation rates. Sampling started in April 1979 and ended in October 1980. Within each forest type, soils from burned coupes had higher mean values for pH, exchangeable cations, percent base saturation, and nitrate-N produced during aerobic incubation, and had lower mean values for exchangeable acidity and ammonium-N produced during aerobic incubation than soils from unburned coupes. In mixed forest only, soils from burned coupes had higher mean values for extractable P and soil phosphate buffering capacity, and lower mean values for total organic C than those of unburned coupes. There were only small differences between burned and unburned soils in cation exchange capacity and ammonium-N produced during anaerobic incubation. For each burned coupe in mixed forest, with increase in time since burning there was a decrease in pH, an increase in exchangeable acidity, and a decrease in rate of production of nitrate: no changes were detected in other factors. It is concluded that, for clay soils developed on dolerite, the nutritional status of soil in both forest types is probably improved by burning. The improvement lasts for more than 4 years in mixed forest and more than two years in dry sclerophyll forest. Only minor leaching of nutrients to below 10 cm in depth is likely to occur in either type.     

酸性森林土壤缓冲酸沉降关键机理研究进展

对有关酸性森林土壤如何缓冲酸沉降的研究进行了综述,从土壤矿物风化与离子交换反应、有机质的作用,和其他生命与非生命因素方面去探讨酸性森林土壤缓冲酸沉降的关键机理,旨在加深人们对酸性森林土壤响应酸沉降模式与缓冲机制的理解,从而更好地预测酸沉降背景下酸性森林土壤的酸化进程及其负面效应,为制定科学合理的森林经营管理措施,维持整个森林生态系统的稳定与生态服务功能提供科学借鉴。     

Significant soil acidification across northern China's grasslands during 1980s–2000s

Anthropogenic acid deposition may lead to soil acidification, with soil buffering capacity regulating the magnitude of any soil pH change. However, little evidence is available from large‐scale observations. Here, we evaluated changes in soil pH across northern China's grasslands over the last two decades using soil profiles obtained from China's Second National Soil Inventory during the 1980s and a more recent regional soil survey during 2001–2005. A transect from the central‐southern Tibetan Plateau to the eastern Inner Mongolian Plateau, where Kriging interpolation provided robust predictions of the spatial distribution of soil pH, was then selected to examine pH changes during the survey period. Our results showed that soil pH in the surface layer had declined significantly over the last two decades, with an overall decrease of 0.63 units (95% confidence interval = 0.54–0.73 units). The decline of soil pH was observed in both alpine grasslands on the Tibetan Plateau and temperate grasslands on the Inner Mongolian Plateau. Soil pH decreased more intensively in low soil carbonate regions, while changes of soil pH showed no significant associations with soil cation exchange capacity. These results suggest that grassland soils across northern China have experienced significant acidification from the 1980s to 2000s, with soil carbonates buffering the increase in soil acidity. The buffering process may induce a large loss of carbon from soil carbonates and thus alter the carbon balance in these globally important ecosystems.     

Nitrification in some tropical soils

Summary Nitrification of soil N in 8 mineral and 2 histosols having a wide range in pH (3.4 to 8.6), organic C (1.22 to 22.70%) and total N (0.09 to 1.20%) was studied by measuring nitrate fromation under aerobic incubation of the soil samples at 30°C for 4 weeks. The amounts of NO₃-N produced in the soils varied from 0 to 123 μg/g of soil. Soil N in the two acid sulfate soils and one other acid soil did not nitrify under conditions that stimulate nitrification. Soils having pH more than 6.0 nitrified at a rapid rate and released NO₃-N ranging from 98 to 123 μg/g. The two organic soils differed considerably in their capacity to nitrify though the total amounts of mineral N released were similar in these soils. The amounts of NO₃-N formed in the soils was highly positively correlated with the soil pH but was not significantly correlated with the organic C of total N content of the soils. Statistical analysis also showed that nitrate formation was not significantly correlated with soil pH in soils having pH higher than 6.0.     

Different performances of soil phosphate tests for reflecting the effects of buffering capacity on uptake of native phosphate with time

The ability of two sodium bicarbonate (Colwell and Olsen) and two ammonium fluoride (Bray I and Bray II) soil tests to reflect the effect of phosphate buffering capacity of the soil on plant growth through time was studied on ten Argentine soils. The soils were divided into three groups (low, medium and high buffering capacity) according to a buffering index calculated from the slope of the Freundlich equation. The relation between phosphate extracted by soil tests and both relative yield and phosphate uptake of rye grass plants was affected by the phosphate buffering capacity of the soil. The effect of buffering on that relation was more marked for the sodium bicarbonate tests (specially Colwell) than for the Bray tests. This effect was consistent with time. Hence, adjustment for buffering would be more important for the sodium bicarbonate tests than for the Bray tests. Soils with high buffering capacity were able to sustain a greater rate of phosphate uptake. The effect of buffering on the relation between soil tests and both relative yield and phosphate uptake was greatest when the plants were young and decreased with time. This effect would therefore be very important for the early nutrition of annual pasture or crop species.     

Oxidation and Mobility of Trivalent Chromium in Manganese-Enriched Clays during Electrokinetic Remediation

This article presents the results of an investigation that assessed the extent and effect of oxidation of Cr(III) in manganese-enriched clays on the electrokinetic remedial efficiency. Because chromium commonly exists along with nickel and cadmium at contaminated sites, the effects of changes in chromium redox chemistry on the migration of the coexisting nickel and cadmium was also studied. Bench-scale electrokinetic experiments were conducted using two different clays: kaolin, a typical low buffering soil, and glacial till, a high buffering soil. Tests were performed with 1000?mg/kg of Cr(III), 500?mg/kg of Ni(II), and 250?mg/kg of Cd(II), both with and without the presence of 1000?mg/kg of manganese. All of these experiments were conducted under a constant voltage gradient of 1.0?VDC/ cm. The experimental results showed that in the presence of manganese, percentages of oxidation of Cr(III) into Cr(VI) ranged from 67% in kaolin to 28% in glacial till even before the application of induced electric potential. The low extent of oxidation of Cr(III) in glacial till may be attributed to the initial precipitation of Cr(III) as Cr(OH)₃ resulting from high soil pH, reducing aqueous Cr(III) concentrations present within the soil. In kaolin, Cr(III), Ni(II), and Cd(II) under electric potential migrated toward cathode and precipitated near the cathode due to high soil pH. When manganese was present in kaolin, Cr(VI) that was formed due to the oxidation of Cr(III) migrated toward anode and adsorbed to the soil surfaces near the anode region due to low soil pH. However, remaining Cr(III) as well as Ni(II), and Cd(II) migrated towards and precipitated near the cathode due to high soil pH. In kaolin, the migration of Ni(II) and Cd(II) was retarded in the presence of manganese due to a larger soil zone of elevated pH near the cathode. In glacial till, the migration of Cr(III), Ni(II) and Cd(II) was insignificant due to precipitation resulting from high soil pH caused by the high buffering capacity of the soil. Cr(VI) that resulted from the partial oxidation of Cr(III) in the presence of manganese, however, migrated toward the anode. Overall, this study demonstrated that the effects of manganese on Cr(III) oxidation in low buffering soils can be significant, which can in turn affect the extent and direction of chromium migration under induced electric potential.     

The effect of pH on the growth of saprotrophic and ectomycorrhizal ammonia fungi in vitro

Some saprotrophic and ectomycorrhizal fungi produce reproductive structures, preferably in slightly alkaline to neutral forest soil. This research examines the growth of these "ammonia fungi" in liquid medium at various pH values. In the first experiment, the capacity of six buffers was examined to select appropriate buffers for stabilizing pH in the neutral-to-alkaline range by culture of three species of the ammonia fungi in media initially adjusted to pH 7, 8 or 9. The highest buffering capacity was shown in 2-(N-morpholino) ethanesulfonic acid (MES) at pH 7, and N, N-bis (2-hydroxyethyl) glycine (Bicine) and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) at pH 8 and 9. In the second experiment, the growth of 15 strains of both saprotrophic and ectomycorrhizal ammonia fungi was tested on the medium initially adjusted to pH 3, 4, 5, 6 or 7 with MES, or to pH 8 or 9 buffered with Bicine. Many of the saprotrophic species grew well at pH 7 or 8; the ectomycorrhizal species showed optimum growth at pH 5 or 6. The pH suitable for the in vitro growth of these fungi was correlated with the pH of forest soil where these fungi occur.     

黄河三角洲不同类型盐生植物土壤真菌群落结构特征

盐生植物种类及其所具有的不同耐盐调节方式影响着根际微生物群落的结构与组成。为明确不同类型盐生植物根际与非根际土壤中真菌群落结构与组成的差异及其与土壤环境间的相互关系,该研究采集了黄河三角洲地区芦苇、盐地碱蓬、獐毛3种不同类型盐生植物0～20 cm土层的根际和非根际土壤,通过高通量测序对其真菌群落多样性和结构进行了分析,以探究真菌群落特征与土壤理化因子间的关系。结果表明：(1)3种不同类型盐生植物根际土壤真菌群落丰富度显著大于各自非根际土,且獐毛根际土壤真菌群落丰富度显著大于芦苇和盐地碱蓬的根际土。(2)距离热图分析表明,芦苇和盐地碱蓬非根际土壤真菌群落间的相似性最大。(3)土壤真菌多样性和丰富度与土壤总碳、总氮、有效磷、pH呈正相关关系,与土壤盐分含量呈负相关关系。(4)3种不同类型盐生植物的根际与非根际土壤中,球囊菌门(Glomeromycota)均为绝对优势门,盾巨孢囊霉属(Scutellospora)为优势属。(5)RDA分析表明,土壤盐分含量是影响土壤真菌群落结构的重要因子,球囊菌门丰度与土壤总氮、总碳、有效磷、有机碳、pH呈正相关关系,与盐分呈负相关关系。(6)植物土壤真菌群...     

Effect of Phosphate Treatment on Pb Leachability in Contaminated Shooting Range Soils

A cost-effective way to reduce lead released into the environment is through immobilization with readily available soil amendments. Leaching of Pb from four shooting range soils treated with two phosphate sources was evaluated in soil columns. Phosphate was applied at a P/Pb molar ratio of 4:1 with two-thirds of the P supplied from phosphate rock (PR) and one-third from phosphoric acid (PA). The soils were incubated for 18 hr and leached with toxicity characterization leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) fluids, respectively. PR/PA treatment reduced Pb in TCLP leachate to below regulatory limit of 5 mg/L after 18 hr of incubation. Reduction of Pb leached was more dependent on clay content than total Fe. PR/PA treatment had no effect on pH of TCLP leached soils, while it led to a drastic lowering of pH that mobilized Pb in SPLP leached soils. However, leaching of Pb reduced with time in SPLP leached soils because pH increased gradually. PR/PA treatment was more effective in SPLP leached soils with low total soil Pb because they received lower amounts of PA. PR/PA treatment may be more efficient when applied as split applications in soils with a low to medium Pb loading and a high buffering capacity.     

施肥和增水对弃耕草地土壤酸中和容量的影响

大气氮沉降增加是草地土壤酸化的主要原因。土壤酸缓冲性能作为评估土壤酸化的重要指标,对氮输入的响应受到降水与其他限制养分含量的影响。本研究以我国北方温带弃耕草地氮、磷、水添加试验13年后的土壤为对象,利用二次多项式模型拟合酸滴定曲线,计算了土壤酸缓冲容量(ABC)以及以pH 5.0和4.0为参比的土壤酸中和容量(ANC)。结果表明: 不增水处理下,单独加氮和同时添加氮磷均显著降低土壤pH,降低以pH 5.0和4.0为参比时的酸中和容量(ANC_pH5.0和ANC_pH4.0);单独加磷对土壤pH、ANC_pH5.0和ANC_pH4.0均无显著影响。增水处理下,加氮及加氮磷显著降低土壤pH、ANC_pH5.0和ANC_pH4.0;加磷显著降低土壤pH,但增加了ANC_pH4.0,而对ANC_pH5.0无显著影响。与不增水处理相比,增水处理对土壤pH、酸中和容量均具有显著的正效应。对于初始pH值不同的土壤,采用土壤酸中和容量比酸缓冲容量能更好地指示土壤抗酸化能力。     

Effect of Soil Chemical and Physical Properties on Sorption and Desorption Behavior of Lead in Different Soils of India

Lead (Pb) is a non-biodegradable contaminant, present in the environment, especially near lead-based industrial sites, agricultural lands, and roadside soils. Bioavailability of Pb in the soil is controlled by the sorption and desorption behavior of Pb, which are further controlled by the soil chemical and physical properties. In this study, sorption and desorption amounts of Pb in soil were compared with soil physical (sand, silt, clay content) and chemical (pH; electrical conductivity, EC; percent organic carbon, (%OC); cation exchange capacity, CEC) properties. Twenty-six surface soils (0–5cm), expected to vary in physical and chemical properties, were collected from different parts of India and were treated with known concentration of Pb solution (40 μg/L). The amount of Pb sorbed and desorbed were measured and correlated with soil properties using simple linear regressions. Sorption was significantly (p ≤ 0.05) and positively correlated with pH, and %OC; desorption was significantly (p ≤ 0.05) negatively correlated with the same two factors. Stepwise multiple regressions were performed for better correlations. Predicted sorption and desorption amounts, based on multiple regression equations, showed reasonably good fit (R² = 0.79 and 0.83, respectively) with observed values. This regression model can be used for estimation of sorption and desorption amounts at contaminated sites.     

Sr-90 transfer factors for rye in podzolic soils: Dependence on soil parameters

The transfer factor (TF) for Sr-90 was studied in 10 rye fields with podzolic soils near Bremen. Values between 0.10 and 0.30 were obtained with a mean of 0.18. The TF was correlated with various soil parameters (pH, organic matter, K, Ca and P content). Negative correlations were found between TF and pH-value, Ca and P content. However, the content of organic matter in the soils was positively correlated with soil and grain activity (Bq/kg).     

Preliminary investigation on Mgbede-20 oil-polluted site in Niger Delta, Nigeria

Soil physicochemical properties (pH, electrical conductivity (EC), % moisture, total organic carbon (TOC), total organic matter (TOM)), total extractable hydrocarbon content (THC), and micronutrient (Mn, Fe, Cu, Zn) levels of the Mgbede-20 oil-impacted site in Niger Delta, Nigeria, were investigated. Both oil-impacted and their background control soils were found to be acidic especially at surface depth. A slightly higher EC value of 107.4+/-15.0 microS cm(-1) was obtained for the subsurface-polluted soils. Of the micronutrients investigated, only Fe exceeded its acceptable limit (>100 mg/kg). The observed increase in moisture content resulting from the oil's aggregation of soil particles may lower soil porosity, and increase resistance to penetration and hydrophobicity. Soil pH can be adjusted by aeration to complete the microbially mediated oxidation of the organic acids, followed by the addition of agricultural lime to provide some buffering capacity to the soil.     

Relation of growth and zinc uptake of rice to quantity,intensity and buffering capacity factors of zinc in soils

Adsorption of zinc in rice soils was studied to define the functional relationship between quantity, intensity and buffering capacity factors of soil zinc to the growth and zinc uptake of rice crop. A supply parameter integrating the quantity, intensity and buffering capacity factors into a single unifying term was computed from the data on Zn adsorption in these soils. A green house experiment was conducted with three soils providing a matrix of different values of supply parameter of Zn to determine the optimum value of this parameter for the proper growth and zinc nutrition of rice crop. Results indicated that a value of this parameter around unity is optimum for sustaining proper growth and zinc nutrition of rice in these soils. The variations in dry matter yield and zinc uptake of rice in different soils may be related to the differences in the physical and chemical properties of the soils.     

The Role of CEC and pH in Cd Retention from Soils of North of Iran

Cadmium (Cd) is a critical environmental chemical in which sorption reactions control its entry into soil solution. The aim of the present study was to evaluate Cd sorption characteristics of some soils of the northern part of Iran with a wide range of physicochemical properties. Duplicates of each sample were equilibrated with solutions containing 5 to 500 mg Cd L^?1 with 0.01 M CaCl₂ as background solution. The quantity of Cd retention was calculated as the difference between initial and equilibrated Cd concentration. Sorption isotherms including Freundlich, Langmuir, Temkin, Dubinin-Radushkevich, and Redlich-Peterson were used to evaluate the behavior of Cd sorption. Cadmium sorption data were well fitted to Langmuir, Freundlich, and Redlich-Peterson isotherms. The constant of Freundlich equation (k_F ) and adsorption maxima (b_L ) of Langmuir equation were related to pH and cation exchange capacity (CEC). The maximum buffering capacity (K_d ) was significantly correlated with pH (R² = 0.52, p ≤ 0.001) and calcium carbonate equivalent (CCE) (R² = 0.63, p ≤ 0.001). Redlich-Peterson constants (k_RP and a_RP ) were significantly correlated with pH (R² k_RP = 0.30, p ≤ 0.007) and (R² a_RP = 0.27, p ≤ 0.012). It seemed that pH, CEC, and CCE were the main soil properties regulating Cd retention behavior of the studied soils.     

近20年来江苏省土壤pH值时空变化及其驱动力

通过比较1980年和2003年江苏省土壤pH空间分布图,发现虽然两个时期土壤pH空间分布的基本格局仍然相似,表现为南酸北碱,但局部地区也存在较大的变化,主要表现为酸化.沂沭岗地浅洼平原土区、里下河浅洼地土区、宁镇扬低山丘陵土区和太湖平原土区均有较严重的酸化出现.分析发现前两者主要受不合理施肥、田间管理和土地利用及种植类型变化的影响,后两者除以上的影响因素外还包括工业化和城市化.另外在后两者和宜溧洞庭山地土区由于土地利用和种植方式的变化、建筑和道路的兴建,还导致了局部地区土壤pH有所上升.土类中潮土酸缓冲性能强、pH变化不大,水稻土pH下降严重,特别是里下河浅洼地土区水稻土,在现有的管理利用方式下,继续下降的可能性很大.     

Acceleration by montmorillonite of nitrification in soil

A soil naturally containing montmorillonite (M) was amended with 10% M and sequentially perfused with glycine, with fresh glycine being added every 16–17 d after nitrification of the previously added glycine-nitrogen had reached a plateau. In some systems, the old perfusates were replaced each time with a fresh glycine solution; in others, the initial perfusate was not replaced but only adjusted each time to the original 200 ml volume and a comparable glycine concentration (140 μg NH₂-N/ml). The incorporation of M enhanced the rates of heterotrophic degradation of glycine and subsequent autotrophic nitrification, but these stimulatory effects decreased with each successive perfusion. The reasons for these decreases are not known, but they did not appear to be related to inorganic nutrition, as perfusion with a mixed cation solution after five perfusion cycles did not significantly enhance nitrification in either the check or M-amended soils during three subsequent perfusions with glycine. The enhancement of nitrification by M appeared to be a result, in part, of the greater buffering capacity of the M-amended soil, as indicated by lesser reductions in the pH of perfusates from the M-amended soil, by titration curves of the soils, and by the greater and longer stimulation of nitrification in the cheek soil amended with 1% CaCO₃, which had a greater buffering capacity than did M. The stimulation by CaCO₃ may also have been partially the result of providing CO₂ for the autotrophic nitrifyers. Significant concentrations of nitrite accumulated only in perfusates from soil amended with CaCO₃. Air-drying and remoistening the soils enhanced nitrification of subsequently added glycine, especially in the check soil. The importance of pH-mediation, of the production of inhibitors, and/or of feed-back inhibition was indicated by the lower rate and extent of nitrification in systems wherein the perfusates were not replaced between successive additions of glycine. Although the results of these studies confirmed previous observations that M enhances the rate of nitrification in soil, the mechanisms responsible for this stimulation are still not known.     

Bradford reactive soil protein in Appalachian soils: distribution and response to incubation, extraction reagent and tannins

Bradford reactive soil protein (BRSP) is thought to correlate to glomalin, an important soil glycoprotein that promotes soil aggregate formation and may represent a significant pool of stable soil organic matter (SOM). However, more information is needed about its importance in Appalachian soils and its relationships with other soil properties. We measured BRSP in 0–20 cm soil from pastures, hayfields, cultivated fields or forest areas in southern West Virginia. Highest amounts of BRSP were found near the soil surface and decreased significantly with depth for all land uses except cultivated sites. Forest and pasture sites contained more BRSP than hayfields or cultivated fields but these differences occurred only in the 0–5 cm depth. Overall averages of C and N in BRSP represented about 4.0 and 6.5% of the total soil C and N respectively. During a 395 day soil incubation, we found CO₂–C evolution rates comparable to other studies but only small changes in BRSP (<10%) including some evidence for increases during incubation. Sodium citrate, sodium pyrophosphate, and sodium oxalate recovered significantly more BRSP from soil than the other extractants we tested with highest extraction efficiencies observed for sodium citrate and pyrophosphate. Recovery of BRSP appears related to negative charge and buffering capacity of both the soil and extractant. Extractants with low negative charge had little buffering capacity and yielded little BRSP. Tannic acid appeared to increase extraction of BRSP but less soluble-N was recovered from tannin-treated samples than from untreated controls and E4/E6, the ratio of absorbance at 465 and 665 nm, decreased, evidence for the formation of larger or heavier molecules. Formation of dark-colored substances during extraction suggests the colorimetric Bradford assay may overestimate soil protein when tannins are present. Recovery of less soluble-N from soil extracts and lower E4/E6 ratios suggests tannins may bind with soil constituents themselves or form non-extractable N-containing complexes.     

Copper Sorption Behavior of Selected Soils of the Oasis in the Middle Reaches of Heihe River Basin,China

The mobility and bioavailability of copper (Cu) depends on the Cu sorption capacity of soil and also on the chemical form of Cu in soils. Laboratory batch experiments were carried out to study the sorption and distribution of Cu in nine soils differing in their physicochemical properties from the oasis in the middle reaches of Heihe river basin, China: desert soil (S-1), agricultural soils (S-2, S-3, S-8, and S-9), marshland soil (S-4), and hungriness shrub soils (S-5 and S-6). Copper sorption behavior was studied using the sorption isotherm and sequential extraction procedure. In general, the sorption capacity for Cu decreased in the order: S-4 > S-9 > S-2 > S-8 > S-3 > S-6 > S-5 > S-7 > S-1. The correlation results suggest that soils with higher CEC, silt, clay, CaCO3, and organic matter will retain Cu more strongly and in greater amounts than soils that are sandy with lower CEC, CaCO3, and organic matter. pH is not an important impact factor to Cu sorption in experimental soil samples because pH in soils used in this study had a narrow range. The distribution of sorbed Cu varied between nine soils studied and depended on both soil properties and initial added Cu concentration. There are significant differences in the distribution of Cu in each soil with the increase of initial Cu concentration. The predominance of Cu associated with the available fraction, which was over 50% of the total sorbed Cu in most cases, indicates that the change of geochemical conditions might promote the release of Cu back into soil solution thus impacting organisms in the soils. The added Cu has also the tendencies to locate in the residual fraction, which was larger than 5% of the total amount extracted from the four fractions in most soils.