how is soil pH determined? I see that in some articles a 1:1 ratio of soil to water is used for determination of pH, and in some papers a 1:5 soil to water ratio is used, what's the difference and which one is a more accurate method?
thanks is advance
Dear Fa,
There is no standard procedure for measuring soil pH. Some of the details that vary from one laboratory to the next are: soil : solution ratio, use of a salt solution (e.g., 0.01 M CaCl2) rather than water, method of mixing, time of standing before reading, etc. Soil may be weighed, or measured as a volume (McLean 1982). Therefore, when reporting sol pH, it is essential to include at least a brief summary of the procedure followed.
The experimental AFNOR standard NF X-31-103 (France) recommends a ratio 1/2.5. The International standard NF ISO 10390 recommends a ratio 1/5. And the USDA - Kellogg Soil Survey Laboratory Methods Manual (Report 42, 2014) suggest to use a ratio 1/1.
With my best regards
Prof. Bachir ACHOUR
Generally, a ratio of 1:5 soil to water is used to determine pH of soil. weigh 20 g of dry soil and add it to 100 mL of water in a conical flask. stir well with a glass rod and allow them to swirl in an orbital shaker for few minutes. Remove the flask and measure the pH of the solution with a well calibrated pH meter.
In my opinion 1:5 ratio (soil to distilled water) is more suitable to determine pH because in this case the natural condition would be simulated in laboratory. I have seen this procedure in many articles.
Dear Fa,
There is no standard procedure for measuring soil pH. Some of the details that vary from one laboratory to the next are: soil : solution ratio, use of a salt solution (e.g., 0.01 M CaCl2) rather than water, method of mixing, time of standing before reading, etc. Soil may be weighed, or measured as a volume (McLean 1982). Therefore, when reporting sol pH, it is essential to include at least a brief summary of the procedure followed.
The experimental AFNOR standard NF X-31-103 (France) recommends a ratio 1/2.5. The International standard NF ISO 10390 recommends a ratio 1/5. And the USDA - Kellogg Soil Survey Laboratory Methods Manual (Report 42, 2014) suggest to use a ratio 1/1.
With my best regards
Prof. Bachir ACHOUR
Adequately explained by Prof. Bachir ACHOUR . However when dealing salt-affected soils it would be better if 1:2 soil :water is followed as per the USDA Handbook 60.Generally for such soils this ratio is suggested for comparison of results from one part to the other part of the globe.
As Prof. Bachir ACHOUR statted, there is no standard procedure for measuring soil pH, it depends on you soil characteristics. But, the most common ratio used for soil-water pH is 1:1 soil:water. Some laboratories measure pH in a 1:2 ratio of soil to deionized to improve the fluidity of the slurry; particularly for soils with high organic matter and clay concentrations that can absorb a significant volume of water.
Hi Najafi,
There are no perfect methods for measuring soil pH. So, the best method depends upon your objective. All of them reflect different approaches and interpretations of soil acidity. However, I suggest you to go for 1:5 method.
Zafar
You can use portable soil pH meter. pH is measured on a scale of 0-14. A soil or water pH reading below 7 is considered acidic, while a pH reading above 7 is basic. A pH reading of 7 is neutral, and is ideal for many plants and spray materials. You can measure both in the field and even after the soil sample collection. If you already have the samples, then follow this method:
Its a great job. However simply speaking you can use a pH meter. pH meter can tell you the pH value. But don't forget to calibrate device before use.
But if I use the 1: 5 ratio, would the soil classification be the same as for the 1: 2.5 ratio? I don't think so.
Of course there is a standard procedure! ISO 10390 describes the measurement of pH in soils. The ratio 1:5 specified there is related to volumes. For example 5 ml soil is suspended in water, 0.01 mol/l CaCl2 or 1 mol/l KCl solution by shaking for 60 min followed by settling for 1 to 3 hours (avoid contact with air during this step). The pH is measured then in the supernatant solution. The values measured in water are about 0.5 - 0.7 higher in comparison to CaCl2 and KCl.
I have just noticed that I skiped the volume of water accidently. For this example (at a ratio of 1:5) of course 20 ml of water or salt solution is applied. Maybe I should also add the explanation that the salt solutions can be take to simulate the natural pore water of soils.
But what about soil classification?
Can i use the same classification for all ratio: 1/2.5, 1/5, 1/10?
Good explanations by Prof. Bachir ACHOUR and Mohammed Abu Sayed Arfin Khan.
Thanks and regards
- Badges
- Science topic
- Similar topics
- Biological Science
- Biochemistry
- Biochemical Techniques
- Analytical Chemistry
- pH