Sodicity

In their model they used a kaolinite-like clay for the degraded silicate and allowed Na, Mg, and K to react to form sodic montmorillonite, chlorite, and illite respectively. The balance is essentially complete with only small residuals for H4Si04 and HCOT The newly formed clays would constitute about 7% of the total mass of sediments. 

Irrigation has been practiced from the ancient time it is only in the twentieth century that the importance of the irrigation water quality was recognized [7]. The use of saline water may result in the reduction of crop yields. A high sodicity of water for irrigation may cause the deterioration in the physical properties of soils... 

Under water scarcity, the two factors, salinity and sodicity of the irrigation water must be considered together for a proper evaluation of the ultimate effect of the water on the infiltration rate that generally increases with increasing salinity of the irrigation water and decreases with either decreasing salinity or increasing sodicity. 

Davidson, J.L. Quirk, J.P. (1961). The influence of dissolved gypsum and pasture establishment on irrigated sodic clays. Australian Journal of Agricultural Research, 12, 100-10. 

Western Woodlaik Basin Franklin Seamount (9°55 S, 151L50 W) 2143-2366 Westernmost propagating tip of spreading center. Basaltic andesite and inferred sodic rhyolite. Spires aud mounds of Fe-Mn-Si oxide up to several meters thick and 200 m in extent. Venting 20-30 C clear solution. Inactive barite silica chimneys contain up to 21 ppm Au. vSi-bearing Fe oxyhydroxide. 

It is sometimes claimed that mucilage and similar gels may help to maintain hydraulic conductivity between root and. soil (52). However, the hydraulic conductivity of soils is often substantially decreased when soils are irrigated with waste water. Apart from the inducement of sodicity, which is real in many cases, the decreases in hydraulic conductivity are attributed largely to the production of microbial biomass, particularly extracellular polysaccharides (e.g.. Ref. 53). These extracellular polysaccharides form gels that may store large quantities of water and allow water and ions to diffu.se through them at rates not much less than those of free water, but they could be expected to restrict mass flow of water and thus nutrients, to roots (54). 

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. 

Sodium Adsorption Ratio. Because of the swelling effects of Na+, the relative amount of sodium (sodicity) in the water quality especially in the irrigation water quality is an important measurement in soil science. Decreased permeability can interfer with the drainage required for normal salinity control and with the normal water supply and aeration required for plant growth. The relative sodium status of irrigation waters and soil solutions is often expressed by the sodium adsorption ratio (SAR)... 

Alkali feldspars (K.NajAlSijOg) form a continuous solid solution series at high temperatures, but tend to exsolve upon cooling into a potassium-rich phase and a sodium-rich phase, resulting in perthitic intergrowths (2). Sodic plagioclases and potassium-rich feldspars tend to be studied together, in part because of similarities in structure, composition, occurrence, and weatherability (e.g., 1[). 

Table I. Silica Release Rates from Sodic Feldspars...

Fig. 8.26 Exchangeable sodium percentage (ESP) along a Burleson soil column, as a function of the sodium adsorption ratio (SAR) of irrigation water. The values were obtained by percolating the soil columns with sodic water (total electrolyte concentration of 11 meq/L). Each curve corresponds to a given applied volume of solution (Thomas and Yaron 1968)...

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... 

Kaersutite NaCa2(Mg,Fe)4TiSi6Al2(0,0H)24 SODIC-CALCIC AMPHIBOLES C2lm... 

Figure 5.40 Intracrystalline distribution of Fe +-Mg + between Ml and M3 sites in sodic amphiboles. Reprinted from Ungaretti et al. (1978) with author s permission.

We recall to this purpose that ideal site mixing does not necessarily mean that the mixture as a whole is ideal, but that the intracrystalline site distribution may be described by a constant (without the necessity of introducing site-interaction parameters cf equation 5.109, for example). Generally speaking, if the adopted constant differs from 1 (as in the case of sodic amphiboles in figure 5.40 and of cummingtonites in figure 5.39), the mixture as a whole is obviously nonideal because site permutability does not reach the maximum value attained by the ideal condition (cf section 3.8.1). 

The extrinsic stability relations of the sodic term paragonite [NaAl2(Si3Al) Ojo(OH)2] have been investigated as have those of the potassic end-member muscovite ... 

---