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United States Department of Agriculture

Agricultural Research Service

Title: Determining Soil & Water Sodicity from Electrode Measurements

Authors
item Rhoades, James
item Manteghi, N
item Lesch, Scott - UCR, RIVERSIDE, CA 92521
item Slovacek, Denton - HACH CO., LOVELAND, CO

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 1997
Publication Date: N/A

Interpretive Summary: The presence of excessive levels of sodium in soils and irrigation waters causes deleterious effects on their use for crop production. This hazard is referred to as sodicity and is a serious problem in some parts of the US and abroad. The reclamation and management of such soils and waters requires appropriate, practical methods for diagnosing sodicity. Conventional methodology takes about seven separate analytical operations to determine the sodium-adsorption-ratio (SAR) which is the traditional index of soil and water sodicity hazard. A much faster and simpler methods were developed and successfully tested on a wide range of salt-affected soils and extract solutions. The methods avoid the need for laboratory analyses of calcium and magnesium concentrations and, in the case of soils, to separate extracts from the saturated soil-pastes. The SAR is sufficiently accurately estimated in the methods using simple electrode measurements made directly in the pastes. The methods were developed under a CRADA with the Hach Company and will soon be available to the public in the form of a test kit.

Technical Abstract: A method was developed for estimating the sodium adsorption ratio (SAR) of the extracts of the saturated-pastes of salt-affected soils from measurements made directly in the saturated-paste with sodium-, EC- and pH-electrodes. An analogous method was developed for the determination of the SAR of extracts and other aqueous solutions when the electrode measurements were made in the extract or solution without the use of pH and ionic strength buffers. The methods were successfully tested on a widespread range of salt-affected soils and extract solutions and were deemed suitable for field applications in the diagnosis, screening and classification of sodic soils and waters. The methods will be available to the public in the form of test-kits manufactured by the Hach Company.

Last Modified: 9/2/2014
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