Response of soils to sodic and saline conditions

Abstract

SALINE AND SODIC SOIL CONDITIONS reduce the value and productivity of soils in the arid and semiarid regions of the world. Accumulation of soluble salt in the soil solution im poses stress on growing crops that can lead to decreased yields and, in severe cases, com plete crop failure. Accumulation of dispersive cations such as sodium and, possibly, potassium in the soil solution and the exchange phase affects soil physical properties such as structural stability, hydraulic conductivity, and infiltration rate, which conse quently affect crop production.Management of saline and sodic soils for crop production involves understanding three interrelated general areas: crop response to saline conditions, simultaneous transport of salt and water in soil, and response of soils to sodic and saline conditions.Although the first area has been studied mainly by plant scientists and agronomists, the second and third areas have been studied mainly by soil scientists. Considerable in formation is available in the technical literature on all three areas, but knowledge in the third area is more limited and empirical than in the first two. Rhoades (1972) and Frenkel et al. (1978), evaluating water quality for irrigation, concluded, "Our greatest limitation in assessing the sodicity hazard [of irrigation water] is our inability to predict how the water will affect soil structure and permeability."An indication of the superficiality of our understanding of the response of soils to sodic and saline conditions is the confusion we face in trying to answer the following five questions.1) What is the critical concentration of exchangeable sodium which separates normal from sodic soils? The US Salinity Laboratory Staff (1954), after studying many soil samples from the western USA, suggested an exchangeable sodium percentage (ESP) of 15 as the critical level above which soil structure could be deleteriously affected. This value was considered to be far too high for Australian soils, and Mclntyre (1979), study ing the hydraulic conductivity of 71 soil samples from Australia, proposed an ESP of 5 more appropriate for separating normal from sodic soils. This difference in the threshold sodium percentage is very important in the applied world. Whereas ESP values above 15 are quite rare in soils of arid and semiarid regions, soils with ESP values around 5 are wide spread. If we adopt the Australian definition, most soils in semiarid and arid regions should be classified as sodic soils and care should be undertaken in their management.

Hydrodynamic and Chemical Factors in Clogging by Montmorillonite in Porous Media

“…With regard to chemical effects, cation valence is known to affect the permeability of soils containing clays (e.g., [17][18] and to influence the morphology of clay aggregates (e.g. , [19][20][21].…”

Long-term application of animal slurries to grassland alters soil cation balance

“…Lebron et al (2002) found that hydraulic conductivity decreased sharply as ESP approached 5%. An ESP of only 2.2% can cause a 70% decrease in infiltration rate (Shainberg & Letey 1984). Soils with a high clay or silt content might be expected to be more sensitive to increased ESP than sandy soils.…”

“…However, soil pH is already greater than 6.0 in the HC treatment without lime having been applied at any time over the 32 years to all but one of the HC plots; thus the addition of lime to supply Ca 2þ and increase soil pH further is not an agronomic option. The addition of gypsum is a possible management strategy to minimize the impact of slurry (Shainberg & Letey 1984;Halliwell et al 2001;Lebron et al 2002). Gypsum can provide the Ca 2þ needed to exchange for Na þ and K þ and maintain a higher electrolyte concentration in solution; it has been shown to improve soil physical conditions (Shainberg & Letey 1984;Sumner 1993;Yu et al 2003) and P retention (Vidal et al 2003).…”

“…Organic manure application alters both chemical and physical properties of soil (Shaviv et al 1986;Christie 1987;Haynes & Naidu 1998;Hao & Chang 2002), which has implications for aspects of the agro-environmental system such as plant nutrient supply and nutrient loss to surface waters. Soil sodicity may be increased, which is known to damage soil structure and alter soil hydraulic properties (Shainberg & Letey 1984;Sumner 1993). Much work has highlighted the risk of nutrient loss, particularly phosphorus (P), from soils receiving organic fertilizers (McGechan 2001; Van Vliet et al 2002) and this has been identified as a major contributor to the eutrophication of surface water bodies.…”

Problem Soils of the Paddy Fields in the Eastern Coastal Plain of the Red River Delta, Vietnam

“…Leaching of salts by irrigation water is inhibited by an unstable soil structure and decline in soil permeability (Shainberg and Letey, 1984). The toxicity of Na ion leads to proper consideration of sodium-divalent cations exchange selectivity and its influence.…”