Alkaline soils calcareousness

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). 

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 ... 

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. 

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... 

Alkaline or calcareous soils cannot be preserved with sodium bisulfate. 

Bray 1 Mehlich 1 Olsen NH4F + HC1 HC1 + H2S04 NaHC03, pH 8.5 non-calcareous soils - often used for tropical soils acid and sandy soils neutral and alkaline soils, but used widely... 

A detailed description of how dissolved CO2 is involved in controlling the pH of alkaline and calcareous soils is useful at this point. 

It may be instructive to analyze in some detail the situation of a reversibly adsorbed ion, whose mobility in the soil is relatively high. A case in point is Cd, a toxic metal that adsorbs by cation exchange in acid and near-neutral soils, but may precipitate into carbonates and phosphates in calcareous and alkaline soils. The theory needed for the analysis of ion leaching through soils, in which the main retention mechanism is ion exchange, is developed in Chapter 3 (section 3.5) using Cs as the example ion. 

Thus, B(0H)3 is a Lewis add rather than a Bronsted acid (see Chapter 1). Because boron adsorbs most effectively in the pH 8 to 9 range on A1 and Fe oxides and silicate minerals, its availability is generally low in coarse-textured, acid-leached soils and in calcareous soils. Deficiency in add soils is the result of boron depletion by leaching, while deficiency in calcareous soils is caused by strong adsorption and predpitation as relatively insoluble Ca borate salts. In contrast, B toxicity is most commonly found in alkaline soils of arid regions these soils often contain high levels of Na which forms quite soluble borate salts. A lack of rainfall allows soluble borate to accumulate to phytotoxic levels. 

Cobalt toxicity is occasionally found in high-Co soils formed from serpentinite and other ultrabasic rocks. Deficiency is most likely in coarse-textured, acid-leached soils alkaline or calcareous soils and humus-rich soils. Extractability by strong acids can range from very little (< 1%) to a large fraction (>30%) of the total Co, depending on the forms of Co in the soil. 

Under acidic, oxidizing conditions, Zn " is one of the most soluble and mobile of the trace metal cations. It does not complex tightly with organic matter at low pH. Acid-leached soils often have Zn deficiency because of depletion of this element in the surface layer. Calcareous and alkaline soils also commonly have Zn deficiency, but the cause is low solubility. 

If a low concentration of Fe , say 10 Af, is maintained in soil solution by cation exchange (or by precipitation of FeCO, as would be the case in calcareous or alkaline soils), then equation 10.85 simplifies to... 

However, based on higher correlation of soil test with crop response, dilute acid fluoride extraction (Bray s No. 1 extractant) or NaHCOg adjusted at pH 8.5 (Olsen s extractant) considering all soils including acid, neutral, alkaline and calcareous are most commonly used for routine soil testing and soil fertility evaluation programme. 

Adsorption of Mo to hydrous Fe and A1 oxides is pH-dependent (Reisenauer, Tabikh, and Stout, 1962), and the rate of adsorption is highest at acidic pH. It decreases with increases in pH from 4.45 to 7.5. Compared with acid soils, alkaline soils are high in soluble or available Mo (Davis, 1956). As in any other soil, in alkaline soil the availability of Mo is also influenced by several other factors. The relative Mo content of the parent rock, the process of soil evolution, and the physicochemical attributes of the soil (pH, calcareousness, organic-matter content, cation-exchange capacity, texture, moisture, relative concentrations of other mineral elements) all influence the availability of Mo. 

Although pH is the predominant factor affecting the availability of Mo in alkaline soils, there are several other factors that influence its availability. Soil calcareousness, cation-exchange capacity (CEC), organic-matter content, and soil moisture are all known to affect the availability of Mo in alkaline soils. 

Mehrotra, N. K., and Agarwala, S. C. (1979). Nutrient composition of rice plants subjected to high alkalinity (SAR) in irrigation waters and soil calcareousness. In Micronutrients in Agriculture, ed. S. C. Agarwala and C. P. Sharma, pp. 95-102. Lucknow, India University of Lucknow. 

The H3PO4 produced in (12.4) moves from the fertiliser granule and dissolves large quantities of Fe + and AF from the clay soil, and becomes involved in the complex chemistry of the salts listed in Table 12.7. In calcareous (alkaline) soils, reaction (12.5) may proceed to some extent, putting the phosphate in less available form. 

The chemistry of calcareous and alkaline soils is dominated by the CaCOj which is present. This absorbs phosphate on its surface converting it to amorphous calcium phosphate (12.5), which is later transformed into crystalline CaHP04 2H2O. The latter then maintains adequate quantities of phosphate in the soil solution. 

Gypsum has a substantial advantage for use in high pH or alkaline soils, because of being pH neutral. This is because the sulfur in the compound lowers soil pH. The presence of gypsum in calcareous soils causes a small decrease in pH through the increased Ca concentration in soil solution which would be expected to decrease the sorption of P (Kordlaghari and Rowell, 2006). 

Because of their phosphatic composition, conodonts will not persist for long in acidic soils. Calcareous parent materials of Paleozoic age commonly contain conodonts, and they may occur in the sand fraction of more alkaline soils. Conodonts are common in the calcareous tills derived from the Paleozoic of the northeastern United States (Sitler [1963] and authors unpublished data). 

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. 

If the weathering rate equals or exceeds the rate of H+ release by the biota, such as would be the case in a calcareous soil, the soil will maintain a buffer in base cations and residual alkalinity. On the other hand, in noncalcareous "acid" soils, the rate of H+ release by the biomass may exceed the rate of H+ consumption by weathering and cause a progressive acidification of the soil. In some instances, the acidic atmospheric deposition may be sufficient to disturb an existing H+ balance... 

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