Sodic soils

The basement complex for the Patagonian desert and arid northeastern Brazil is formed by metamorphosed Precambrian rocks. Landscapes are characterized by level erosion surfaces of different ages. The landscape is dissected by a large number of valleys. Large depressions are filled with marine and continental beds of sedimentary rocks. Rocks in the Andean system, that stretches the entire length of the west side of the continent, vary greatly. Many depressions are filled with sediments. In addition, many active volcanoes are responsible for periodic lava flows and the deposition of volcanic ash. East of the Andes, the land surface is level and slopes towards the Atlantic Ocean. Broad depressions contain saline or sodic soils. 

Swarup A., Anand S. Transformation and availability of iron and manganese in submerged sodic soils in relation to yield and nutrition of rice. Fertilizer News 1989 34 21-23. 

Bethune MG, Batey TJ (2002) Impact on soil hydraulic properties resulting from irrigating saline-sodic soils with low sahnity water. Austral J Exp Agri 42 273-279 Birnbaum LS, Sttaskal DE (2004) Brominated fiame retardants Cause for concern Environ Health Perspectives 112 9-17... 

Bresler E, McNeal BL, Carter DL (1982) Saline and sodic soils. Advanced series in agricultural sciences 10 Springer-Verlag, Berlin... 

Rengasamy, P. (2002) Transient salinity and subsoil constraints to dryland farming in Australian sodic soils an overview.- Australian Journal of Experimental Agriculture 42, 351-361. 

Garg, V.K., Singh, P.K. and Katiyar, R.S. (2004) Yield, mineral composition and quality of coriander (Coriandrum sativum) and fennel (Foeniculum vulgare) grown in sodic soil. Indian journal of Agricultural Sciences 74(4), 221-223. 

Coale, F. J., V. P. Evangelou, and J. H. Grove. 1984, Effects of saline-sodic soil chemistry on soybean mineral composition and stomatal resistance. J. Environ. Qual. 13 635-639. 

Reeve, R. C. and C. A. Bower. 1960. Use of high-salt water as a flocculant and source of divalent cations for reclaiming sodic soils. Soil Sci. 90 139-144. 

Hydration swelling, 108-115 Layer charge and CEC, 113-115 Structure, 111 Sodic soils, 407 Dispersion, 414 Exchangeable Na+, 409, 412 Toxicity to plants, 407-408 Sodium, 411... 

Gupta, R.K., Chhabra, R., and Arbol, I.P., Fluorine adsorption behavior in alkali soils Relative roles of pH and sodicity, Soil Sci., 133, 364, 1982. 

Karyotis, T., Iliadis, C., Noulas, C., and Mitsibonas, T. (2003). Preliminary research on seed production and nutrient content for certain quinoa varieties in a saline-sodic. Soil ]. Agron. Crop Sci. 189, 402 08. 

J. Akhter, R. Murray, K. Mahmood et al.. Improvement of Degraded Physical Properties of a Saline-Sodic Soil by Reclamation with Kallar Grass (Leptochloa fusca), Plant Soil, 258(1), 207-216, Jan. (2004). 

R.P. Courtemanche, M.W. Hester, and LA. Mendelssohn, Recovery of a Louisiana Barrier Island Marsh Plant Community Following Extensive Hurricane-induced Overwash, J. Coastal Res. 15(4), 872-883, Fall (1999). G. Singh, H. Singh, and P.P. Bhojvaid, Amelioration of Sodic Soils by Trees for Wheat and Oat Production, Land Degrad. Devel. 9(5), 453 62, Sept.-Oct. (1998). 

In semiarid climates, sulfate deposits in the soil are sometimes reduced under conditions of poor drainage. The conditions necessary for reduction are created in natural basins where water accumulates due to the very low water permeability of sodic soils. The sulfate reduction reaction ... 

Wetlands of humid climatic zones often emit H2S, as is evident from the rotten-egg odor of marshes and swamps. As long as the dominant exchangeable base cations are Ca " and Mg ", which is the case in most freshwater wetlands, H2S formation should not cause the soils to become strongly alkaline. In these nonsodic soils, alkalinity generated by reduction forms precipitates of Ca (and Mg) carbonates. The low solubility of these carbonates prevents the pH from rising much above 8. In sodic soils, however, reaction 7.64 causes alkalinity to build up in the form of soluble Na carbonates (see Chapter 8, Section 8.1). 

Figure 8.4. Relative cation composition of exchange sites for sodic soils compared with nonsodic ("normal" and acid) soils. (Adapted from G. H. Bolt et al. 1976. Adsorption of cations by soil. In G. H. Bolt and M.G.M. Bruggenwert (eds.). Soil Chemistry. New YorIcElsevier.)...

The typical compositional range of exchange sites in soils, shown in Figure 8.4, reveals that sodic soils have higher than normal levels of exchangeable Na" ". The important ionic concentrations in soil solution that affect the level of exchangeable Na are [Na" ], [Ca " ], and [Mg +], The sodium adsorption ratio, or SAR, is a solution property defined by the equation... 

There are basically three potential hazards of salt-degraded soils to plants—salinity, sodicity, and alkalinity. The first two hazards are used to classify soils as saline or sodic, or both, as described in Table 8.4. The alkalinity hazard (measured by RSC) is not usually applied directly to the classification of soils, but the pH values reported in Table 8.4 indicate that sodic soils are the most likely to have a problem of high alkaUnity. This arises partly from the hydrolytic exchange reaction, described in Chapter 3, which is enabled by the presence of appreciable exchangeable Na" and low salt concentrations, conditions that are diagnostic of sodic soils. Hydrolytic exchange can be viewed as a two-step reaction ... 

The leaching of saline-sodic soil with good water (low salinity, low SAR) causes the pH to rise. This can result in the mobilization of trace elements such as selenium in some soils (selenium exists in the soil as an oxyanion, selenite or selenate), elements that adsorb better at low pH than high pH. How would you prevent this potential environmental risk to groundwater during the reclamation of the saline-sodic soil ... 

In calcareous soils, F mobility is low. Perhaps its solubility is limited by incorporation into insoluble Ca minerals such as hydroxyapatite. In sodic soils, F" mobility is enhanced by the fact that NaF is a very soluble salt. 

Halite Halides Arid, saline/sodic soils C Highly soluble adverse osmotic effects on plants... 

Gypsum Sulfates Arid soils C Moderataly-high solubility used to reclaim sodic soils... 

Sodic (black alkali) soils are a particularly difficult management problem. The water permeability of these soils to water is very slow. The pH of sodic soils is commonly greater than 9 or 9,5, and the clay and organic fractions are dispersed. Dispersed organic matter accumulates at the surface of poorly drained areas as water evaporates and imparts a black color to the surface, hence the name black alkali. Sodic soils are found in many parts of the western United States. In some locations they occur in small patches, slick spots, less than 0.5 ha in extent. Such patches occupy slight depressions, which become accentuated as surface soil particles disperse and are blown away by wind erosion. The percolation of insufficient water to satisfy plants and to control salinity is the main problem associated with sodic soils. In addition, their relatively low soluble-salt concentrations and high pH values can result in direct Na toxicities to the most sensitive plants. 

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