Ratio soil/solution

Soil solution to soil ratios also strongly affect distribution of some trace elements such as Zn speciation in arid and semi-arid soils. Fotovat et al. (1997) reported that the proportion of free hydrated Zn2+ to total Zn ranged from 20-65% at field capacity soil water content and decreased with increases in solution to soil ratios, while the proportion of Zn complexed with organic ligands increased dramatically in soils. However, solution to soil ratios do not strongly affect the distribution of Cu speciation in soil solution since Cu primarily occurs as organic complexes in these soil solutions. 

Step No. Fraction Solid-phase desired Reagents pH Ratio of solution/soil Temperature (°C) Time Note... 

Both ratio of base cations to aluminum, and the aluminum concentrations, are used as indicators for steady-state geochemical and biogeochemical processes. By assigning established critical loads to these indicators (for example, the concentrations of aluminum in soil solution should not exceed 0.2 meq/L and the base cations to aluminum ratio should not be less than 1), it is possible to compute the allowable acidification for each ecosystem. An extensive overview of critical values for the ratio of base cations to aluminum for a large variety of plants and trees can be found in Prof. Sverdrup s papers (for example, Sverdrup et al., 1995 Warfvinge et al., 1992, 1993). 

Sverdrup, H., Warfvinge, P., Rosen, K. (1995). A model for the impact of soil solution Ca Al ratio, soil moisture and temperature on tree base cation uptake. Water, Air and Soil Pollution, 61, 365-383. 

A further difficulty is the distinction between a concept and an operation, for example in the definition of ion exchange capacity. Operationally, "the ion exchange capacity of a soil (or of soil-minerals in waters or sediments) is the number of moles of adsorbed ion charge that can be desorbed from unit mass of soil, under given conditions of temperature, pressure, soil solution composition, and soil-solution mass ratio" (Sposito, 1989). The measurement of an ion exchange capacity usually involves the replacement of (native) readily exchangeable ions by a "standard" cation or anion. 

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)... 

The selectivity of the exchange between two cations is specific to saline snbsnr-face systems, described by the sodium adsorption ratio (SAR). Based on Na content in soil solutions, the U.S. Salinity Laboratory (U.S. Salinity Laboratory 1954) derived the equation... 

Kj, or the ratios of solution-phase solute concentration and adsorbed-phase concentration were calculated to estimate the relative affinity of the soils for phenolic acids. The Kj values for p-hydroxybenzoic acid, p-coumaric, vanillic, ferulic, and syringic icids were 67, 75, 69, 92 and 376, respectively for a 48-hr equilibration of 0.1 nmol mL phenolic acid solution with a sample of an alfisol preextracted in boiling water. The sorption capacity was greatly reduced by pretreatment of soil samples with sodium acetate-hydrogen peroxide to remove organic matter and metal sesquioxides. 

Albrecht campaigned against the concept of an acid soil causing poorer crop growth rather, it is the calcium deficiency that needs to be remedied. The acid soil solution dissolves rock particles, such as rock phosphate and limestone, to release beneficial nutrients such as phosphate and calcium respectively. It also mobilizes the other adsorbed ions off the clay-humus colloid. He estimated the optimum ratios of calcium to magnesium and calcium to potassium. These were approximately from 4 1 to 7.5 1, and from 15 1 to 38 1 respectively. The higher the Ca K ratio, the more proteinaceous... 

Overman, A. R., and Chu, R. L. (1977a). A kinetic model of steady state phosphorus fixation in a batch reactor. I. Effect of soil/solution ratio. Water Res. 11, 771-775. 

With respect to trace metal cations, it is common in soil solutions for the total cation anion ratio of the reactants to be very low because complexing anions are... 

Chapman, RJ., Edwards, A.C. and Shand, C.A. (1997) The phosphorus composition of soil solutions and soil leachates influence of soil solution ratio. Eur. J. Soil Sci., 48, 703-710. 

As silicate minerals decompose, trace elements are released and enter the soil solution. Thereafter their fate depends on a number of factors. Immediately, they may precipitate or remain in solution and the likelihood of this happening can be predicted by considering the ion s charge/radius (in nm) ratio, which is often called the ionic potential (IP). Values of IP > 95 refer to soluble anions of the elements B, Cr(VI), Mo(VI), Si and W. Soluble cations are found in a group where IP < 30, namely Cd, Co, Cu, Fe(II), Pb, Mn(II), Hg, Ni, Ag, Sr, Sn and Zn. 

The most important factor influencing the uptake of strontium by plants is the Ca status of the soil, other factors include the pH and organic matter content. Lem-brechts et al. (1990) have investigated the relation between soil solution composition and 85Sr uptake by young lettuce plants. A close relationship was shown between the Sr concentrations in the plants and the Sr/Ca ratio in solution either in nutrient medium, or in soil solution. It was suggested that plants primarily withdraw their nutrients from the soil liquid phase. 

As an example of these ideas, an activity-ratio diagram for control of Al(III) solubility by secondary minerals in an acidic soil solution will be constructed. The Jackson-Sherman weathering scenario14 indicates that when soil profiles are leached free of silica with fresh water, 2 1 layer-type clay minerals are replaced by 1 1 layer-type clay minerals, and ultimately these are replaced by metal oxyhydroxides. This sequence of clay mineral transformations can be represented by the successive dissolution reactions of smectite, kaolinite, and gibbsite ... 

---