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One of the most important factors limiting plant growth is soil pH. The objective of this study is to determine the effectiveness of marble waste applications on neutralization of soil acidity. Marble quarry waste (MQW) and marble cutting waste (MCW) were applied to an acid soil at different rates and their effectiveness on neutralization was evaluated by a laboratory incubation test. The results showed that soil pH increased from 4.71 to 6.36 and 6.84 by applications of MCW and MQW, respectively. It was suggested that MQW and MCW could be used as soil amendments for the neutralization of acid soils and thus the negative impact of marble wastes on the environment could be reduced. [Copyright &y& Elsevier]

The mechanisms by which organic materials affect soil pH are not fully understood. This study for the first time compared the short-term effect of various model organic compounds on pH change of two soils differing in initial pH (Podosol of pH 4.4 and Tenosol of pH 6.1). Eight organic compounds, representing common compounds in plant residues, were selected based on the number and type of chemical functional groups. The addition of organic acids (acetic, malic, citric, and benzoic acid) reduced soil pH immediately due to H dissociation. The magnitude of pH decrease depended on the rate of application, degree of dissociation of the acids, and initial soil pH. During a subsequent incubation, pH was slowly restored as these compounds were decomposed. The degree to which pH was restored was reduced with increasing addition rate. The production of H ions was increased with increasing rate of acid addition and decreased over time. When potassium citrate (organic anion) was added, soil pH increased due to H consumption upon decomposition. Compounds with amine groups (glucosamine hydrochloride) and less easily decomposable compounds (phenol) did not significantly alter pH during 16-day shaking. Changes in pH after glucose addition were relatively small compared with other compounds and were not expected because hydroxyl chemical groups of glucose are neutral. The present study demonstrated that the addition of model organic compounds to soil caused soil pH to increase, decrease, or remains unaffected. The extent and direction of pH change was dependent on the chemical functional group, addition rate, decomposition, and the initial soil pH. [ABSTRACT FROM AUTHOR]

We determined the effects of wood ash fertilization, given together with nitrogen (WAN), and nitrogen given together with P, B and Cu (SSF), on soil and foliage nutrients and fine root biomass in a 45-year-old Norway spruce stand in southern Finland. Fine roots were sampled 9 years, and the soil 10 years after ash (3 t/ha) and nitrogen (150 kg/ha) application. Fine root biomass tended to be lower, the necromass higher, and the fine root distribution relatively deeper on the WAN than on the control and SSF plots. The response of fine root biomass to WAN was probably related to changes in soil acidity. pH, base saturation, total and extractable concentrations of Ca, K, Mg and P, and total B, Cd, Mn, Ni and Zn concentrations in the organic layer were significantly higher on the WAN plots than on the SSF and the control plots with no ash and nutrient addition. On the WAN plots, the pH was 1.2 pH-units higher, the exchangeable Ca concentrations fourfold and those of Mg over twofold compared to the control plots. WAN increased the concentrations of K but decreased those of Mn and Ni in the needles compared to the control and SSF treatment. Even though ash and nitrogen fertilisation tended to decrease the fine root biomass, this decrease was not likely to affect tree growth during a 10-year period. [ABSTRACT FROM AUTHOR]

Incubation of soil with CaCO3 is generally considered a reliable method to determine the lime requirement (LR) of acid soils. Because of their considered reliability, these incubations are often used to calibrate buffer methods; however, one study reported that the use of room temperature incubation with CaCO3 overestimated the actual LR determined by field testing. The objective of this study was to compare the pH change following CaCO3 incubations for 60 d with those following 3-d incubations with Ca(OH)2 and to determine the possible role of soil N reactions causing any differences in pH change. Seventeen soils were incubated with either CaCO3 for 60 d at approximately 85% field capacity or for 3 d with an equivalent amount of Ca(OH)2 solution plus water to maintain a 1:1 soil/solution ratio. Both were incubated at room temperature (23 ± 2°C), followed by measurement of pH (1:1 in water). Ammonium-N and NO3--N were analyzed at Days 0 and 60 of the incubation. Soil pH was lower following the 60-d CaCO3 incubation than after the 3-d incubation with Ca(OH)2. The analysis of N transformations indicated that positive values of H+ (more H+ was produced than consumed) were generated from nitrification after 60 d of incubation in 14 out of 17 soils. Furthermore, incubations with soils that have been air dried produced a flush of nitrification that increased the ionic strength and decreased pH even further. These effects from long-term incubation would erroneously increase the LR. Incubation with Ca(OH)2 for 2 to 4 d avoids these errors. [ABSTRACT FROM AUTHOR]

Arsenic (As) concentrations in soils and waste material in two areas of former As mining and processing: Złoty Stok (Złote Mts.) and Żeleźniak (Kaczawskie Mts.), SW Poland, were measured to assess levels and environmental risk associated with possible increases in arsenic mobility under changing pH and redox conditions. Twenty six soil samples were collected from 12 sites, and represented a broad spectrum of soil properties and parent material origin, including natural soils, mine spoils, slags and tailings. Arsenic species were examined using a sequential extraction technique. The changes in As solubility were determined from extraction test solutions adjusted to solution pH values varying from 2 to 8. The effects of reducing conditions on As mobility were examined in incubation tests. Most of soils demonstrated extremely high concentrations of As, both of natural and anthropogenic origin. Total As concentrations in all samples were in the range 100–43,500 mg/kg. Sequential extraction techniques suggested that the main species of As in all soils were those bound to iron (Fe) oxides, in particular amorphous ones, whereas the contributions of mobile and specifically sorbed As forms were relatively low. In tailings and tailings-affected alluvial soils, As occurred mainly in residual forms, however these soils also had considerable amounts of mobile As. In all other soils, mobile As forms were very low. Arsenic mobilization could be possible at extremely low or high pH conditions (pH<2 or pH>8), and this may be of particular practical importance in the case of tailings, which are highly alkaline. High pH promotes solubilization of As forms in reducing conditions, whereas in neutral and acidic soils the risk of As release under reducing conditions is limited. [Copyright &y& Elsevier]

Soybean [Glycine max (L.) Merrill] often shows symptoms of iron deficiency chlorosis (IDC) on high pH, calcareous soils of the U.S. Midwest. The objective of this study was to assess the variation in soybean yield that could be explained by soil pH and carbonate concentration in Iowa fields. Color aerial images of soybean canopy taken from 2000 to 2002 from 12 fields having acid to calcareous soils were used to select 10 to 28 sampling areas 10 to 25 m² in size to encompass significant variability in early soybean growth and IDC symptoms in each field. Representative areas 0.93 m² in size were identified through field observations to collect soil samples and measure grain yield. Soil pH measured to a 15-cm depth across fields ranged from 5.6 to 8.2 and calcium carbonate equivalent (CCE) ranged from 0 to 30%. Soil CCE varied from 2.5 to 30% as pH ranged from 7.7 to 8.2. Grain yield decreased with increasing pH and CCE in 9 and 11 fields, respectively. Soil pH and CCE explained 30 and 41% of the variability in relative yield across sites, respectively. An alkalinity stress index (ASI) that combined both measurements (pH + 0.14CCE) was developed based on the relative effects of each measurement on yield and explained 45% of the yield variability across sites. The index developed was a better predictor of soybean yield in fields with high-pH soils than each measurement alone. [ABSTRACT FROM AUTHOR]

Two polycyclic aromatic hydrocarbon (PAH)-contaminated soils of pH 2 were successfully used as inoculum to enrich cultures growing on phenanthrene and pyrene at different pHs, including pH 3. Selected pyrene-utilizing cultures obtained at pH 3, pH 5, and pH 7 were further characterized. All showed rapid [14C]pyrene mineralization at pH 3 and pH 5 and grew on pyrene at pH values ranging from 2 to 6. Eubacterial and mycobacterial 16S rRNA gene denaturing gradient gel electrophoresis fingerprinting and sequencing indicated that the cultures were dominated by a single bacterium closely related to Mycobacterium montefiorense, belonging to the slow-growing Mycobacterium sp. In contrast, a culture enriched on pyrene at pH 7 from a slightly alkaline soil sampled at the same site was dominated by Pseudomonasputida and a fast-growing Mycobacterium sp. The M. montefiorense-related species dominating the pyrene-utilizing cultures enriched from the acidic soils was also the dominant Mycobacterium species in the acidic soils. Our data indicate that a slow-growing Mycobacterium species is involved in PAH degradation in that culture and show that bacteria able to degrade high-molecular-weight PAHs at low pH are present in acidic PAH-contaminated soil. [ABSTRACT FROM AUTHOR]

Abstract: The pH-dependent charges of Hungarian soils have been studied via surface acid–base properties. The intrinsic stability constants of protonation and deprotonation processes, as well as the concentration of surface sites, have been determined by surface complexation modeling. The protonation and deprotonation constants have been nearly the same for most soils. There is a relation between the concentration of surface sites and composition, expect for the freshly deposited soils with high primary silicate content. The results show that the concentrations of silanol and aluminol sites are different for each soil, the intrinsic stability constants of protonation and deprotonation processes, however, are nearly the same within experimental error. This can only be explained if these stability constants are real thermodynamic equilibrium constants. The fact that these constants are nearly the same supports the conclusion that we succeeded in excluding all processes that would disturb the measurements. The parameters characteristic of the edge sites of the soils are of two types: (a) the parameters depending on the quality and composition of the soils, (i.e.), the concentration of surface sites; (b) the parameters depending on the thermodynamically well-defined acid–base processes, independent of soil composition. [Copyright &y& Elsevier]

As Brachiaria hybrid cv. 'Mulato' has adapted to acid soils with extremely low phosphorus (P) contents, its low-P-tolerance mechanisms were investigated and compared with those of wheat (Triticum aestivum L.) and rice (Oryza sativa L. cv. 'Kitaake'). Among the three plant species, the highest P-use efficiency (PUE) in low-P soil was recorded in the Brachiaria hybrid, which increased remarkably under P-deficiency and soil acidity, while P-deficiency had less effect on the PUE of wheat and rice. As exudation of organic acid anions from roots is considered to be one of the most important mechanisms of adaptation to low-P soil, the role of phosphoenolpyruvate carboxylase (PEPC), which is closely related to organic acid metabolism and Pi recycling in C3 plants, was studied. As expected, the PEPC activity of the Brachiaria hybrid (C4 plant) leaves was 51- to 129-fold higher than that estimated for wheat and rice (both C3 plants). PEPC activity in leaves and roots of the Brachiaria hybrid increased up to two-and three-fold, respectively, and decreased the malate-inhibition ratio in leaves in response to P-deficiency. However, PEPC activity and malate-inhibition ratio were less affected in wheat and rice under P-deficiency. The Brachiaria hybrid synthesized higher amounts of organic acids (e.g., oxalate and fumarate) in leaves, especially under P-deficiency. Results from these experiments indicate that PEPC activated in the Brachiaria hybrid under low-P and low-pH conditions may contribute to the plant's greater adaptation to tropical acid soils with P-low availability. [ABSTRACT FROM AUTHOR]

There is an assumption in much recent literature that secreted organic anions (OAs) protect the root meristem from Al toxicity by complexation of Al ions. In fact, several possible mechanisms exist by which common OA might afford some degree of protection. Plants can excrete OA which undergo chemical association with protons (hereafter referred to as protonation) in the soil and increase rhizosphere pH. The cost in reduced carbon relative to protons consumed, C:H+, ranges from 2–6. The efficiency of this mechanism can be enhanced in the presence of soil organisms which can oxidise the OA that remain dissociated at soil pH to CO2 and H2O, thereby consuming protons which associate with lower p K functional groups (p K 1.2 to ~ 4). For fully dissociated organic acids the C:H+ ratio decreases to the range 1–3. The C cost to plants is further minimised if MnO2 is the terminal electron acceptor rather than O2, resulting in C:H+<1. OA might also complex or chelate Al. Complexes of Al3+ with oxalate appear to be effective, with some C:H+≤1. However, citrate complexation appears to be more stable in pure solutions and might offer the additional benefit of enhanced P acquisition. Our assessment is that the most efficient strategy for a plant to employ to protect itself from Al toxicity is to increase pH near the root apex by secreting OA into soil where the microbial oxidation of reduced C could be coupled with the reduction of MnO2. This would consume 0.2–0.67 mole of C per H+, which is the order of magnitude better than the C:H+ ratio of 2–6 that would occur if only protonation of OA was to be relied upon. These mechanisms have implications for the effectiveness of programs aimed at selecting cultivars for resistance to acidic soils. [ABSTRACT FROM AUTHOR]

Many soil analysis labs routinely determine lime requirement of acidic soils using different buffer solutions for optimum plant growth. The Adams‐Evans lime determination solution was introduced more than 40 years ago and has been used by many soil analysis labs. Even though many buffer solutions have been developed since then, very little attention has been paid to address the toxic nature of chemicals involved in buffer solutions. The most commonly used buffer solutions, such as the Adams-Evans, Shoemaker‐McLean‐Pratt (SMP), Woodruff, and others, contain p ‐nitrophenol, which is toxic to humans and the environment. Use of p ‐nitrophenol requires prescribed containment and disposal procedures, that creates extra burden on soil analysis labs that provide their invaluable service at low cost. Replacing p ‐nitrophenol with monobasic potassium phosphate (KH 2 PO 4 ), which has similar buffering capacity but with no known toxicity, is beneficial to soil testing labs and the environment. The original Adams‐Evans buffer solution was compared with the modified Adams‐Evans buffer solution with soils of different pH, cation exchange capacity and lime requirement. The linear regression between the buffer pH values and lime recommendations made by Adams‐Evans and the modified Adams‐Evans solutions were highly significant. Thus, the modified Adams‐Evans buffer solution can be used without loss of established recommendation criteria as the original buffer solution. [ABSTRACT FROM AUTHOR]

Due to their high, degree of reactivity, Mn oxides in soil systems may exert a greater influence on trace metal chemistry than that suggested by their relatively low abundance. In particular, Mn is the only known oxidizer of trivalent Cr in soils. We investigated soil properties that influence the Cr oxidizing capacity of Mn oxides in eight well-aerated high Mn soils. Total and easily reducible Mn abundance were quantified by extraction with 1.5 M NH2OH-HCl and 0.02 M hydroquinone. Relative average Mn oxidation state in soil samples was determined by x-ray absorption near edge structure spectroscopy (Mn-XANES) main edge energy position. Soils ranged in percentage of NH2OH-HCl-extractable Mn between 0.14 and 1.27, pH between 4.4 and 7.2, and percentage of C between 9.0 and 27.2. Manganese- XANES spectra showed that most of the study soils had a high Mn(IV)/Mn(III) ratio with edge energy position intermediate to that of a synthetic birnessite and a synthetic pyrolusite. In these high Mn soils, Mn-XANES edge energy was positively correlated with soil pH, suggesting a linear increase, over the normal range of soil pH, in the Mn(IV)/Mn(III) ratio of soil oxides. Soils with more total reducible Mn generally demonstrated greater net Cr(VI) production, but this pattern was moderated by soil pH and relative Mn oxidation state. High Mn soils with low pH and Mn oxidation state were weaker Cr oxidizers than their Mn abundance would suggest. Our data provide evidence that greater Mn abundance and greater Mn(IV)/Mn(III) ratio in soil Mn oxides enhances Cr oxidation. [ABSTRACT FROM AUTHOR]

A field experiment with five lime rates (0, 3.75, 7.50, 11.25, and 15.00 Mg ha-1) was maintained on a red soil (Ultisol) for 15 years to determine changes of soil acidity and effect on crop yields. The soil acidity decreased while exchangeable Ca in plough layer (0-20 cm) increased with lime rate and time. The decreased subsoil (20-60 cm) acidity started to occur four years after liming, and the extent of decreased soil acidity increased with lime rate and time. The increased ranges of exchangeable Mg2+ in subsoil were greater than that of exchangeable Ca2+, suggesting that downward movement of Mg2+ into the subsoil was faster than that of Ca2+. Lime application significantly increased the yields of crops studied. During the period of experiment, the maximum yield increased 4.67 times for barley, 2.24 times for mungbean, 57.3% for wheat, 53.4% for sesame, 52.8% for broad bean, 44.1% for potato, 35.1% for rapeseed, 32.1% for cotton, 28.4% for corn, 18.5% for watermelon, 11.0% for cowpea and 8.8 % for soybean. Liming at the highest rate was in favor to the decline in subsoil acidity and yield increase, especially for the later period of the experiment. Residual effects of reducing soil acidity by liming for the treatments of 0.5 L, 1.0 L, 1.5 L, and 2.0 L could last for 5, 7, 12, and 14 years, respectively, and the effects of lime application on the yields could last for more than 15 years. [ABSTRACT FROM AUTHOR]

A simple method for titrating acidic soils could be used by soil testing laboratories as an alternative method for routinely determining the lime requirement (LR) of soils. Because soil pH as a function of added base is linear in the pH range of 4.5 to 6.5, it may be possible to determine the slope of this relationship by regression analysis using a minimum number of base additions. The LR could then be determined by calculating the corresponding amount of lime required to reach the target pH using the regression equation. Our objectives were to determine reaction times needed for saturated Ca(OH)2 solution to reach an equilibrium pH with 17 widely different soils, and then test a simple titration procedure for its ability to predict the LR, determined first by a full titration curve and then by a standard incubation method. All titrations were performed in a 1:1 soil/water ratio with calcium hydroxide as the base. Using the regression procedure to estimate LR, equilibration times of 30 rain between base additions gave greater LRs than 15-min equilibration, but the same as 45-min equilibration. When all 17 soils were considered, the LR from extrapolation of the linear regression yielded the same, as did the full titration curve (TC). The LR from titration with three base additions and 30-min equilibration time between additions estimated an average of 80% of the LR determined by the 3-d incubation. The Adams-Evans (AE) buffer procedure overestimated and underestimated the LR for soils with relatively Iow- and high-LRs, respectively. Based on these results, titration appears promising for routine use, but it needs more research to determine whether it can be simplified further. [ABSTRACT FROM AUTHOR]

Liming is an effective method of correcting soil acidity, but the cost and other factors, such as sub-soil acidity, topography, and nutrient availability may limit its benefits. An alternative option is to grow acid tolerant plants. Pot experiments are an effective way of identifying plants with the genetic potential to grow in acidic soils. These experiments require a range of acidity levels. The soil used in this study was a sandy loam. Increments of aluminum sulfate [Al2(SO4)3.18H2O] and calcium carbonate (CaCO3) were added to derive dose-pH response relationships. The derived relationships were used to estimate the quantity of aluminum sulfate and lime required to change the pHCa (1:5, w:v, soil:10 mM CaCl2) of the soil from 4.4 to 3.89 and 4.4 to 5.2, respectively. The estimated quantities of aluminum sulfate (380 g) and calcium carbonate (48 g) were thoroughly mixed through 100 kg batches of the soil, which was potted (2 kg/pot). Then the acidified soils were leached to remove excess salts. The initial pHCa achieved was 3.86 and rose to 3.94 after leaching. A wide range of soluble aluminum (Al) concentrations (1:5, w:v, soil:10 mM CaCl2) was obtained from this study, e.g., 52 mg Al/kg soil in acidified soil and 1.8 mg Al/kg soil in limed soil. The variation in pH and EC between replicate pots was negligible (range 0.05 pH and 0.02 dS/m) and these remained relatively unchanged after six months. During the next six months some pots were held in the laboratory with 3 wetting/drying cycles; however, most were placed outdoors where they were sown with seed of Austrodanthonia spp. During this time, the pHCa of the acidified soils increased slightly to: 4.10 (laboratory), 4.18 (outdoors without plants), and 4.20 (outdoors with plants). A similar increasing trend was also observed in limed soils. It was concluded that adding aluminum sulfate and calcium carbonate followed by washing with water are quick and convenient methods for adjusting soil pH for pot experiments. [ABSTRACT FROM AUTHOR]

Only very limited information exists on the plasticity in size and structure of fine root systems, and fine root morphology of mature trees as a function of environmental variation. Six northwest German old-growth beech forests (Fagus sylvatica L.) differing in precipitation (520 – 1030 mm year-1) and soil acidity/fertility (acidic infertile to basic fertile) were studied by soil coring for stand totals of fine root biomass (0–40 cm plus organic horizons), vertical and horizontal root distribution patterns, the fine root necromass/biomass ratio, and fine root morphology (root specific surface area, root tip frequency, and degree of mycorrhizal infection). Stand total of fine root biomass, and vertical and horizontal fine root distribution patterns were similar in beech stands on acidic infertile and basic fertile soils. In five of six stands, stand fine root biomass ranged between 320 and 470 g m-2; fine root density showed an exponential decrease with soil depth in all profiles irrespective of soil type. An exceptionally small stand fine root biomass (<150 g m-2) was found in the driest stand with 520 mm year-1 of rainfall. In all stands, fine root morphological parameters changed markedly from the topsoil to the lower profile; differences in fine root morphology among the six stands, however, were remarkably small. Two parameters, the necromass/biomass ratio and fine root tip density (tips per soil volume), however, were both much higher in acidic than basic soils. We conclude that variation in soil acidity and fertility only weakly influences fine root system size and morphology of F. sylvatica, but affects root system structure and, probably, fine root mortality. It is hypothesized that high root tip densities in acidic infertile soils compensate for low nutrient supply rates, and large necromasses are a consequence of adverse soil chemical conditions. Data from a literature survey support the view that rainfall is another major environmental factor that influences the stand fine root biomass of F. sylvatica. [ABSTRACT FROM AUTHOR]

Summary: In an acid pasture soil (pHCaCl2 of 0–10 cm layer = 4.0) on the Southern Tableland, New South Wales, Australia, the earthworm population was dominated by native species. Aporrectodea trapezoides, a common introduced species reported elsewhere made up <20&percnt; of the total earthworm population with the exception of an area around a tree stump (an old sheep camp) where it was found in greater abundance. Three years after conversion of the pasture area to cropping, abundance of A. trapezoides in the limed plots (4.4 t&sol;ha) was 6.3 times that of the unlimed plots (19.7 vs 3.1 per m–2). A significant positive relationship between abundance and soil pH was detected. Regression analysis indicated that abundance reduced to zero at pH = 4.0. Earthworm distribution around the old tree stump also suggested the adverse effect of acid pH on the abundance of A. trapezoides. On the other hand, significantly lower abundance of the native species was found in the close vicinity of the tree stump (< 10 m) where pH was >5.0. [Copyright &y& Elsevier]

Four maize cultivars, which differ in tolerance to acid soils under field conditions (Zea mays L., acid soil-tolerant C 525 M, BR 201 F and Adour 250, and acid soil-sensitive HS 7777) were used to study the influence of pH (4.3 and 6.0) and Al (0, 20 and 50 µM) on the elongation of seminal roots in nutrient solution. Root elongation was inhibited by high H+ concentrations (pH 4.3) in cultivars C 525 M, Adour 250 and HS 7777 but not in BR 201 F. After 20 h exposure to Al, root elongation rates were more inhibited in cultivars BR 201 F and HS 7777 than in C 525 M and Adour 250. The use of a computerized linear displacement transducer system with high resolution (1 µm) allowed the monitoring of short-term responses of root elongation to Al. In the three cultivars affected by H+ toxicity, but not in the acid-tolerant BR 201 F, Al supply caused an immediate, but transient increase of relative root elongation rates. This result supports the hypothesis that Al-induced growth stimulation is caused by amelioration of proton toxicity. The time required for 20 µM Al to induce a 5% decrease of root elongation rates was shorter in the Al-sensitive BR 201 F (33 min) and HS 7777 (86 min) than in the Al-tolerant C 525 M (112 min) and Adour 250 (146 min) cultivars. However, the response-time to Al may be overestimated in the proton-sensitive cultivars, due to the transient stimulation of root elongation rates induced by Al. According to our results, experiments intended to investigate primary mechanisms of Al toxicity should be started after less than 30 min exposure to toxic Al concentrations, using pH conditions which avoid Al-induced growth stimulation due to amelioration of proton toxicity. [ABSTRACT FROM AUTHOR]