Soil calcareous

Eor example, beryUium occurs at the bottom of a displacement series with NTA allowing this metal to be recovered as the hydroxide by pH adjustment of an ore processing solution all of the interfering metals remain sequestered by chelation (14). Additionally, because other metals present caimot displace iron in an iron—EHPG chelate, the chelate can be used in highly calcareous soils to supply iron as a trace nutrient in agriculture (15). 

Generally, the most common cations in the soil solution are potassium, sodium, magnesium and calcium. Alkali soils are high in sodium and potassium, while calcareous soils contain predominantly magnesium and calcium. Salts of all four of these elements tend to accelerate metallic corrosion by the mechanisms mentioned. The alkaline earth elements, calcium and magnesium, however, tend to form insoluble oxides and carbonates in nonacid conditions. These insoluble precipitates may result in a protective layer on the metal surface and reduced corrosive activity. 

Rijnaarts HHM, A Bachmann, JC Jumelet, AJB Zehnder (1990) Effect of desorption and intraparticle mass transfer on the aerobic biomineralization of alpha-hexachlorocyclohexane in a contaminated calcareous soil. Environ Sci Technol 24 1349-1354. 

One example, a candidate matrix material of organotin species in marine water, had stability determined by storage for 120 days at 4°C in the dark, at ambient temperature, and exposed to daylight (Quevauviller and Donard 1991). Frequently storage at different temperatures over at least a i-year period are reported. Examples include organochlorine pesticides (OCPs) in BCR CRM 430, where pork fat was stored at -2o°C, -i-20°C, and -r37°C (van der Paauw et al. 1992). Storage at -20°C, -i-20°C, and -i-4o°C was performed for total and methyl Hg in BCR CRMs 463 and 464, tuna fish (Quevauviller et al. 1994), and metals in BCR CRM 600, EDTA and DTPA-extractable trace metal contents in calcareous soil (Quevauviller et al. 1998m). 

Quevauviller Ph, Lachica M, Barahona E, Gomez A, Rauret G, Ure A, Muntau H (1998m) Certified reference material for the quality control of EDTA- and DTPA-extractable trace metal contents in calcareous soil (CRM 600). Fresenius J Anal Chem 360 505-511. 

Quevauviller Ph, Herzig R. and Muntau H (1996b) Certified reference material of lichen (CRM 482) for the quality control of trace element biomonitoring. Sci Total Environ 187 143-152 Quevauviller Ph, Lachica M., Barahona E, Rauret G, Ure A, Gomez A, and Muntau H (1997) The certification of the EDTA-extractable contents (mass fractions) of Cd, Cr, Ni, Pb, and Zn and of the DTPA-extractable contents (mass fractions) of Cd and Ni in calcareous soil by the extraction procedures given CRM 600. EUR Report 17555 Quevauviller Ph. Maier EA, and Griepink B, eds. (1995) Quality Assurance for Environmental Analysis. Elsevier. Amsterdam. 

Phosphorus (P) is one of the major limiting factors for plant growth in many soils. Plant availability of inorganic phosphorus (Pi) can be limited by formation of sparingly soluble Ca phosphates, particularly in alkaline and calcareous soils by adsorption to Fe- and Al-oxide surfaces in acid soils and by formation of Fe/ Al-P complexes with humic acids (94). Phosphorus deficiency can significantly alter the composition of root exudates in a way that is, at least in some plant species, related to an increased ability for mobilization of sparingly soluble P sources (29,31,71). 

Especially in dicotyledonous plant species such as tomato, chickpea, and white lupin (82,111), with a high cation/anion uptake ratio, PEPC-mediated biosynthesis of carboxylates may also be linked to excessive net uptake of cations due to inhibition of uptake and assimilation of nitrate under P-deficient conditions (Fig. 5) (17,111,115). Excess uptake of cations is balanced by enhanced net re-lea,se of protons (82,111,116), provided by increased bio.synthesis of organic acids via PEPC as a constituent of the intracellular pH-stat mechanism (117). In these plants, P deficiency-mediated proton extrusion leads to rhizosphere acidification, which can contribute to the. solubilization of acid soluble Ca phosphates in calcareous soils (Fig. 5) (34,118,119). In some species (e.g., chickpea, white lupin, oil-seed rape, buckwheat), the enhanced net release of protons is associated with increased exudation of carboxylates, whereas in tomato, carboxylate exudation was negligible despite intense proton extrusion (82,120). 

From the ecological point of view, strategy II has advantages over strategy I, especially in well-buffered calcareous soils with high pH, since Fe mobilization and Fe uptake by strategy II is less dependent on the external (soil) pH than strategy I (180). 

Formation of stable chelates with phytosiderophores occurs with Fe but also with Zn, Cu, Co, and Mn (Fig. 8) (39,207,208) and can mediate the extraction of considerable amounts of Zn, Mn, Cu, and even Cd in calcareous soils (204,209). There is increasing evidence that PS release in graminaceous plants is also stimulated in response to Zn deficiency (210-212), but possibly also under Mn and Cu deficiency (213). Similar to Fe deficiency, the tolerance of different graminaceous plant species to Zn deficiency was found to be related to the amount of released PS (211,212), but correlation within cultivars of the same species seems to be low (214). It is, however, still a matter of debate as to what extent PS release is a specific response to deficiencies of the various inicronutrients. Cries et al. (213) reported that exudation of PS in Fe-deficient barley was about 15-30 times greater than PS release in response to Zn, Mn, and Cu deficiency. In contrast, PS exudation in Zn-deficient bread wheat was in a similar range as PS... 

Despite increased citrate accumulation in roots of Zn-deficient rice plants, root exudation of citrate was not enhanced. However, in distinct adapted rice cultivars, enhanced release of citrate could be observed in the presence of high bicarbonate concentrations in the rooting medium, a stress factor, which is frequently associated with Fe and Zn deficiency in calcareous soils (235) (Hajibo-huid, unpublished). This bicarbonate-induced citrate exudation has been related to improved Zn acquisition in bicarbonate-tolerant and Zn-efficient rice genotypes (Fig. 9) (23S). Increased exudation of sugars, amino acids, and phenolic compounds in response to Zn deficiency has been reported for various dicotyledonous and monocotyledonous plant species and seems to be related to increased... 

F. Awad, V. Romheld, and H. Marschner, Mobilization of ferric iron from a calcareous soil by plant-borne chelators (phytosiderophores). J. Plant Niitr. // 70l (1988). 

M. Treeby, H. Mar.schner, and V. Roniheld, Mobilization of iron and other micronu-trient cations from a calcareous soil by plant-borne, microbial, and synthetic metal chelators. Plant Soil 114 211 (1989). 

F. Awad and V. Rdmheld, Mobilization of heavy metals from contaminated calcareous soils by plant-borne chelators and its uptake by wheat plants. J. Plant Nutr. 23 (2000) in press. 

J. T. Moraghan, Manganese toxicity in flax growing on certain calcareous soils low in available iron. Soil Sci. Soc. Am. J. 43 177 (1979). 

X. L. Li. E. George, and H. Marschner, Extension of the phosphorus depletion zone in VA-mycorrhizal white clover in calcareous. soil. Plant and Soil I3I 4 (1991). X. L. Li, E. George, and H. Marschner, Acquisition of phosphorus and copper by VA-mycorrhizal hyphac and root-to-shoot transport in white clover. Plant and Soil 135 49 (1991). 

D. B. Alexander and D. A. Zuberer, Respon.ses by iron-efficient and inefficient oat cultivars to inoculation with siderophore-producing bacteria in a calcareous soil. Biol. Fert. Soih. I6 8 (1993). 

Badawy et al. (2002) reported that in near neutral and alkaline soils, representative alluvial, desertic and calcareous soils of Egypt, lead activity ranged from 10 677 to 10 4 83 M, and was negatively correlated with soil and soil solution pH. It could be predicted in soil solution from the equation log (Pb2+) = 9.9-2pH. In German noncontaminated soil with 2.3% CaC03 and soil pH 8.5, Zn, Cu and Cd are 1.87, 0.66, and 0.20 pM/L in soil solution, respectively (Helal et al., 1996). 

Carbon dioxide-water systems play an important role in controlling the pH of alkaline and calcareous soils as well as adjusting solubility of most trace elements and their compounds. Carbon dioxide dissolves in water to form dissolved C02 and dissociated carbonic acid, H2CO30 ... 

In arid and semi-arid soils with a pH range of 6-9, free calcium is the major Ca speciation form in soil solution. When pH > 9.2-9.5, CaP04 becomes a major calcium species in soil solution of neutral and calcareous soils, especially when the activity of H2P04 is > 10 5 M (Lindsay, 1979), such as after phosphate fertilizers are used. Lindsay (1979) further pointed out that CaS04° contributes significantly to the total calcium in solution when S042- is > 10 M. 

Emmerich et al. (1982) reported that in soil solution of arid soils amended with sewage sludge, free Ni2+ ion accounted for 60-70% of the total Ni in soil solution. Sposito and Page (1984) indicated NiHC03+ and NiC03° were also important Ni speciations in alkaline and calcareous soils. 

Figure 3.2. Changes of Cd speciation in soil solutions of a typical Israeli calcareous soil with pH 4-9 (after Hirsh and Banin, 1990, with permission from Soil Sci. Soc. Am)...

Hirsh and Banin (1990) reported that an increase in Cl concentration decreased Cd sorption due to formation of the CdCl+ ion pair. Enhanced sorption in the presence of HC03 was observed due to the formation of the CdHC03+ ion pair. Mahler et al. (1980) found that in calcareous soils treated with sewage sludge spiked with CdS04, Cd complexes were mainly Cd sulfate and carbonate complexes, and the formation of Cd-Cl complexes increased in both soils as total Cd increased. In sludge-amended California soils with pH 7-8, both Cd and Zn organic complexes and Cd phosphate complexes increase with P levels, but free Cd2+ and Zn2+ decrease with P levels (Fig. 3.4) (Villarroel et al., 1993). 

Most primary and secondary minerals found in soil systems are barely soluble in the soil solution. The amount of mass from the bulk phase to hydrated ions in soil solution is negligible compared to the total mass of the solid phase. In arid and semi-arid soils, concentrations of most trace metals in soil solution may be controlled by their carbonates and to some extent by their hydroxides. Other than carbonates, trace elements in arid and semi-arid soils may also occur as sulfate, phosphate or siliceous compounds, or as a minor component adsorbed on the surface of various solid phase components. The solubility of carbonates, sulfates and other common minerals of trace elements in arid and semi-arid soils will be discussed in Chapter 5. Badawy et al. (2002) reported that in near neutral and alkaline soils representative of alluvial, desertic and calcareous soils of Egypt, the measured Pb2+ activities were undersaturated with regard to the solubility of... 

In arid and semi-arid soils, calcite, dolomite, leonhardite (Ca2Al4Si8024.7H20) and lawsonite (CaAl2Si208.2H20) can be possible minerals. Calcium carbonate strongly influences soil properties in arid and semi-arid soils. Most calcareous soils have soil a pH in the range of 7.3-8 5. When sodium is predominant in soils, soil pH is above 8.5. In most arid and semi-arid soils, calcium carbonates (calcite and dolomite) generally accumulate and are most likely to control the Ca2+ and Mg2+ solubility in these soils (Lindsay, 1979). 

Trace elements can be precipitated as carbonates, sulfates, phosphates and hydroxides in arid and semi-arid environments. But most carbonates are more stable in arid and semi-arid soils than other solid phases. Cadmium hydroxide (Cd(OH)2), sulfate (CdS04) and phosphates (Cd3(P04)2) are more soluble than carbonate (CdC03, octavite), therefore the former minerals are not stable in arid soils. In calcareous soils, CdC03 (octavite) is the main Cd mineral to control Cd2+ activity in soil solution. At high C02... 

Soil pH strongly affects adsorption of Cd, Zn, and Pb in soils, but less so for Cu. In addition, Ca2+ is the major soil solution cation of arid soils. Ca2+ has been shown to be important in inhibiting divalent heavy metal sorption in calcareous soils. Theoretically, the presence of Ca2+ in soil solution may reduce metal adsorption in arid soils. However, high pH increases overall metal adsorption in arid soils. 

The protocol involving NaOAc-HOAc at pH 5 was first proposed and used by Jackson (1958) to remove carbonates from calcareous soils to analyze soil cation exchange characteristics (Grossman and Millet, 1961). Other researchers used HOAc for the extraction of metals from sediments and soils (Nissenbaum, 1972 Mclaren and Crawford, 1973). Tessier et al. (1979) first used the NaOAc-HOAc solution at pH 5 to dissolve the carbonate fraction from sediments. Since then, the NaOAc-HOAc buffer has been widely used as a specific extractant for the carbonate phase in various media (Tessier et al., 1979 Hickey and Kittrick, 1984 Rapin et al., 1986 Mahan et al., 1987 Han et al., 1992 Clevenger, 1990 Banin et al., 1990). Despite its widespread use, this step is not free from difficulties, and further optimization is required in its application. Questions arise with regard to this step in the elemental extraction from noncalcareous soils, the dissolution capacity and dissolution rates imposed by the buffer at various pHs, and the possibility that different carbonate minerals may require different extraction protocols (Grossman and Millet, 1961 Tessier et al., 1979). 

Dissolution of carbonate by NaOAc-HOAc solutions at varying pHs from arid-zone soils, as indicated by X-ray diffraction, are presented in Fig. 4.1. Arid soils from Israel contained varying contents of CaC03 (from 13.7-68.1%). X-ray diffraction showed that calcareous soils used in this study... 

The effective dissolution capacity of the NaOAc-HOAc buffer solutions at various pHs in the CARB step of the current SSD protocol is estimated from the maximum quantity of Ca released (Fig. 4.2). When the buffer solution is at pH 5.0, almost all CaC03 can be dissolved from calcareous soils with about 45-50% CaC03 at this step. For soils with higher carbonate contents, a second dose of the buffer solution must be added to complete the dissolution step. 

The contents of trace elements extracted by the buffer solutions depend upon the solution s acid capacity in dissolving carbonate from soils. Trace elements dissolved by the buffer solution increased with decreasing pH of the buffer solution (Table 4.3). Release of trace elements by the buffer solutions at pH 6.0 was much smaller from calcareous soils with more than 30% of CaCC>3. The dissolution of trace elements by the buffers paralleled with the dissolution of Ca and Mg. The correlation coefficients between Ca and trace elements were as follows Cd (0.92), Pb (0.87), Zn (0.90), Ni (0.90), Cr (0.91), V (0.54) and Co (0.70) and between Mg and trace elements were Cd (0.88), Pb (0.80), Zn (0.79), Ni (0.87), Cr (0.58), V (0.69) and Co (0.80), (all with n = 32). 

Extraction of the CARB fraction by the NaOAc-HOAc solution at various pHs resulted in the larger differences obtained in the subsequent fractions, i.e., ERO fraction, OM fraction, and to some extent, the RO fraction (Figs. 4.4 and 4.5). Extraction of the CARB fraction by NaOAc-HOAc solutions at pH 6.0 and 7.0 usually led to higher contents of major and trace elements in the ERO fraction than that by the buffer solutions at pH 4.0 and 5.0. This was especially obvious for Ca and Mg in calcareous soils. Metal extraction from the OM and RO fractions after extraction of the CARB fraction by the NaOAc-HOAc solutions at pH 7.0 and 6.0 were also higher than those extracted by the buffer solutions at pH 4.0 and 5.0, as shown in Figs. 4.4 and 4.5. 

The effects of the pH of the NaOAc-HOAc solutions on the subsequent fractions are related to the partitioning patterns of elements in soils. Calcium and Cd in the calcareous soils are predominately present in the CARB fraction (Banin et al., 1990). Cadmium and Ca in the CARB fraction of the soils studied accounted for 40-50% and 75-99%, respectively. Even NaOAc-HOAc solutions at pH 7.0 extracted 3-6% and... 

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