I have two methods for measuring the ph of soil
the first consists of using 5g of soil with 25 ml of distilled water, stirring for 2 hours and measuring the ph after 24 hours of rest.
the second consists of using 10g of soil with 25 ml of distilled water, shaking for 1 hour and measuring the ph after 2 hours of rest.
the two methods give similar results but if I measure the ph using a sample from the second method but after 24 hours I find that the ph value has changed, for example if I measure the value after 2 hours I find 7.92 and if I leave the sample for 24 hours the value becomes 7.72
so I want to know why there's this change and what's the best method to use
Temperature plays a key role in pH measurements. When temperature levels increase, the pH level drops. Time can indeed affect the pH of a solution, if one (or more) of its components are thermodynamically unstable. In such case, the kinetics of the unstable compound (compounds) reaction will determine the rate of pH change (if it ever changes, it depends on the reactants/products). Atmospheric CO2 also effect the pH of soil. Soil pH will influence both the availability of soil nutrients to plants and how the nutrients react with each other. Soil pH increased with aridity. Soil available P was not significantly affected by aridity. With increasing temperature from cool to warm sites, soil organic C, total N, available N and total P also decreased. In contrast, soil pH and available P increased with temperature.
It is also related to concentration as well, you are increasing concentration 2 times in the 2nd experiment, and as a result, the amount of salts dissolved in water results in pH difference. Another possibility is that insoluble constituents that contribute to pH are higher after 1h of stirring and after prolonged duration that sediment resulting in pH difference.
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