The sodium adsorption ratio (SAR) is an irrigation water quality parameter used in the management of sodium-affected soils. It is an indicator of the suitability of water for use in agricultural irrigation, as determined from the concentrations of the main alkaline and earth alkaline cations present in the water. It is also a standard diagnostic parameter for the sodicity hazard of a soil, as determined from analysis of pore water extracted from the soil.[1]
The formula for calculating the sodium adsorption ratio (SAR) is:[2]
SAR allows assessment of the state of flocculation or of dispersion of clay aggregates in a soil. Sodium and potassium ions facilitate the dispersion of clay particles while calcium and magnesium promote their flocculation. The behaviour of clay aggregates influences the soil structure and affects the permeability of the soil on which directly depends the water infiltration rate. It is important to accurately know the nature and the concentrations of cations at which the flocculation occurs: critical flocculation concentration (CFC). The SAR parameter is also used to determine the stability of colloids in suspension in water.
Although SAR is only one factor in determining the suitability of water for irrigation, in general, the higher the sodium adsorption ratio, the less suitable the water is for irrigation. Irrigation using water with high sodium adsorption ratio may require soil amendments to prevent long-term damage to the soil.[3]
If irrigation water with a high SAR is applied to a soil for years, the sodium in the water can displace the calcium and magnesium in the soil. This will cause a decrease in the ability of the soil to form stable aggregates and a loss of soil structure and tilth. This will also lead to a decrease in infiltration and permeability of the soil to water, leading to problems with crop production. Sandy soils will have less problems, but fine-textured soils will have severe problems if SAR is greater than 9. When SAR is less than 3, there will not be a problem.[4]
The concept of SAR addresses only the effects of sodium on the stability of soil aggregates. However, high K and Mg concentrations have also negative effects on soil permeability. The effect of potassium can be similarly treated by means of the potassium adsorption ratio (PAR).[5] To take into account simultaneously all major cations present in water, a new irrigation water quality parameter was defined: the cation ratio of structural stability (CROSS), a generalization of SAR.[6][7]
^Reeve, R. C.; Bower, C. A.; Brooks, R. H.; Gschwend, F. B. (1954). "A comparison of the effects of exchangeable sodium and potassium upon the physical condition of soils". Soil Science Society of America Journal. 18 (2): 130. doi:10.2136/sssaj1954.03615995001800020004x.
^Oster, J. D.; Sposito, Garrison (1980). "The Gapon coefficient and the exchangeable sodium percentage-sodium adsorption ratio relation". Soil Science Society of America Journal. 44 (2): 258. doi:10.2136/sssaj1980.03615995004400020011x.
^DWAF (1996). "South African Water Quality Guidelines: Vol. 4: Agricultural Use: Irrigation" (PDF). Department of Water Affairs and Forestry, South Africa. pp. 141–153. Retrieved 21 June 2017.
^Rollins, Larry (1 October 2007). "Advanced topics in water chemistry and salinity". WateReuse Foundation. Retrieved 2 November 2016.
^Sposito Garrison (2008) The Chemistry of Soils. 2nd ed. New York. Oxford University Press.
^Rengasamy, Pichu; Marchuk, Alla (2011). "Cation ratio of soil structural stability (CROSS)" (PDF). Soil Research. 49 (3): 280. doi:10.1071/SR10105.
^Smith, Chris J.; Sposito, Garrison; Oster, J.D. (2016). "Accounting for potassium and magnesium in irrigation water quality assessment" (PDF). California Agriculture. 70 (2): 71. doi:10.3733/ca.v070n02p71.
External linksedit
PDF file retrieved 24 December 2008.
January 01, 1970
sodium, adsorption, ratio, sodium, adsorption, ratio, irrigation, water, quality, parameter, used, management, sodium, affected, soils, indicator, suitability, water, agricultural, irrigation, determined, from, concentrations, main, alkaline, earth, alkaline, . The sodium adsorption ratio SAR is an irrigation water quality parameter used in the management of sodium affected soils It is an indicator of the suitability of water for use in agricultural irrigation as determined from the concentrations of the main alkaline and earth alkaline cations present in the water It is also a standard diagnostic parameter for the sodicity hazard of a soil as determined from analysis of pore water extracted from the soil 1 The formula for calculating the sodium adsorption ratio SAR is 2 SAR N a 1 2 C a 2 M g 2 displaystyle text SAR frac Na sqrt tfrac 1 2 Ca 2 Mg 2 where sodium calcium and magnesium concentrations are expressed in milliequivalents liter SAR allows assessment of the state of flocculation or of dispersion of clay aggregates in a soil Sodium and potassium ions facilitate the dispersion of clay particles while calcium and magnesium promote their flocculation The behaviour of clay aggregates influences the soil structure and affects the permeability of the soil on which directly depends the water infiltration rate It is important to accurately know the nature and the concentrations of cations at which the flocculation occurs critical flocculation concentration CFC The SAR parameter is also used to determine the stability of colloids in suspension in water Although SAR is only one factor in determining the suitability of water for irrigation in general the higher the sodium adsorption ratio the less suitable the water is for irrigation Irrigation using water with high sodium adsorption ratio may require soil amendments to prevent long term damage to the soil 3 If irrigation water with a high SAR is applied to a soil for years the sodium in the water can displace the calcium and magnesium in the soil This will cause a decrease in the ability of the soil to form stable aggregates and a loss of soil structure and tilth This will also lead to a decrease in infiltration and permeability of the soil to water leading to problems with crop production Sandy soils will have less problems but fine textured soils will have severe problems if SAR is greater than 9 When SAR is less than 3 there will not be a problem 4 The concept of SAR addresses only the effects of sodium on the stability of soil aggregates However high K and Mg concentrations have also negative effects on soil permeability The effect of potassium can be similarly treated by means of the potassium adsorption ratio PAR 5 To take into account simultaneously all major cations present in water a new irrigation water quality parameter was defined the cation ratio of structural stability CROSS a generalization of SAR 6 7 See also editCation exchange capacity CEC Alkaline soil Residual Sodium Carbonate IndexReferences edit Reeve R C Bower C A Brooks R H Gschwend F B 1954 A comparison of the effects of exchangeable sodium and potassium upon the physical condition of soils Soil Science Society of America Journal 18 2 130 doi 10 2136 sssaj1954 03615995001800020004x Oster J D Sposito Garrison 1980 The Gapon coefficient and the exchangeable sodium percentage sodium adsorption ratio relation Soil Science Society of America Journal 44 2 258 doi 10 2136 sssaj1980 03615995004400020011x DWAF 1996 South African Water Quality Guidelines Vol 4 Agricultural Use Irrigation PDF Department of Water Affairs and Forestry South Africa pp 141 153 Retrieved 21 June 2017 Rollins Larry 1 October 2007 Advanced topics in water chemistry and salinity WateReuse Foundation Retrieved 2 November 2016 Sposito Garrison 2008 The Chemistry of Soils 2nd ed New York Oxford University Press Rengasamy Pichu Marchuk Alla 2011 Cation ratio of soil structural stability CROSS PDF Soil Research 49 3 280 doi 10 1071 SR10105 Smith Chris J Sposito Garrison Oster J D 2016 Accounting for potassium and magnesium in irrigation water quality assessment PDF California Agriculture 70 2 71 doi 10 3733 ca v070n02p71 External links editNew Mexico State University Irrigation water classification systems PDF file retrieved 24 December 2008 Retrieved from https en wikipedia org w index php title Sodium adsorption ratio amp oldid 1138525894, wikipedia, wiki, book, books, library,
