When preparing a saturation paste of soil to test Electrical Conductivity preparation would pulverizing the soil release salts that would have otherwise not been availble for plant uptake? Causing higher EC values?
Is it better to just leave soil as is to better mimick the natural environment that the roots of plants would experience?
Hi Kristin,
If one needs to determine the actual salinity experienced by plant roots in real-time field conditions, measurement of EC (ECw) and solutes in the soil water extracted at field-water content is the best approach. However, it is impractical to routinely extract soil water at typical field-water contents. Therefore, EC of the soil solution extracts obtained at a higher than normal water content (saturated paste) has been used as the best practical method for expressing EC of a given soil. If the EC measurements were made according to the recommended standards, comparisons can be made across studies and soils for which EC has been measured following the same standards.
The standard method for ECe measurement can be found in ‘Methods of Soil Analysis (Part 3), Chemical Methods’ Soil Science Society of America Book Series No.5 (chapter 14). If you cannot access this easily, please let me know, I can provide a pdf.
Susantha
The very purpose of doing EC in saturation paste of soil , instead of soil : water suspension , is simply to emulate the same field conditions almost similar salt infested conditions . And , in the process , soil should never be allowed to under any such mechanical disturbances like pulverization , where there is some possibility of breaking the soil aggregates stabilization . In a way , you are right Kristin .
Standard method for determining ECe (Electrical conductivity in saturation paste) recommends using air dry soils that has been passed through 2.00 mm sieve.
I read about passing it through a 2mm sieve in an article, however I'm thinking that if ECe or saturated paste extract is used to emulate field conditions that roots experience would it not be more ideal to disturbe the soil as little as possible as it may release more salts than would be readily available to plant roots in the environment?
Soluble salts in soil are estimated in extracts of saturated paste or 1:2 and 1:5 soil to water mixture by vacuum filtration. As has been highlighted the saturated paste method is the preferred one. For saline or sodic soil characterization, the saturation paste method is preferred.For routine soil testing purpose, 1:2 soil: water extraction method is used.With dry soil, if we increase the proportion of water,there will be hydrolysis of sparingly soluble salts like gypsum and the salt content estimated will increase.The EC values estimated in 1:2 and 1;5 extracts will be less because of dilution. .So the estimated EC values in 1:2 and 1:5 are multiplied with 2 and 5 respectively to get the EC of the soil(more or less equal to EC of saturation paste).
;:ware
Hi Kristin,
If one needs to determine the actual salinity experienced by plant roots in real-time field conditions, measurement of EC (ECw) and solutes in the soil water extracted at field-water content is the best approach. However, it is impractical to routinely extract soil water at typical field-water contents. Therefore, EC of the soil solution extracts obtained at a higher than normal water content (saturated paste) has been used as the best practical method for expressing EC of a given soil. If the EC measurements were made according to the recommended standards, comparisons can be made across studies and soils for which EC has been measured following the same standards.
The standard method for ECe measurement can be found in ‘Methods of Soil Analysis (Part 3), Chemical Methods’ Soil Science Society of America Book Series No.5 (chapter 14). If you cannot access this easily, please let me know, I can provide a pdf.
Susantha
Hi Kristin,
Susantha hit the nail on the head: you need to use the 'standard' method that suit the soil type and what it is you need to know. You can perhaps use the more exacting techniques in a research study than is possible in day-to-day testing.
Paul.
Pulverizing the soil will alter the field condition as the interstices would have been destroyed and the objective of the work defeated.
Pulverizing/grinding helps in homogenizing soil sample after mixing sub samples and reducing subsampling errors if any.For most of routine analysis, the ground samples are passed through 2-mm sieve .Mechanical grinding using soil grinding machine may be harsher than manual mortar and pestle grinding.In saturation paste preparation spatula is used for mixing and stirring which may not be a harsh treatment.Compared to grinding and working with spatula,the soil:water ratio(increase in proposition of water from field capacity to saturation and other ratios of soil to water )may solubilize some salts present in soil.
Simple standard procedure of soil preparation after passing through 2mm sieve , and subjecting thus prepared soil samples to saturation paste ECe will be the right course . Pulverising soil samples or grinding soils samples using pestle-mortel will not change the mechanical composition of soil to an extent where your EC will not be over-estimated .
The very term salt answers your question. Salts are water soluble. Regardless of their chemical bondage to other compounds, once exposed to water they are released. Even mechanically held salts are released.
Pulverizing the sample give you a clearer and more precise analysis but in many cases should be unnecessary. Leaving the sample whole only means you have fooled yourself, not the sample.
- Badges
- Science topic
- Similar topics
- Agricultural Science
- Soil Science
- Soil Analysis