@ Wati, probably in winter season you are applying more nitrogen and sulfur fertilizers which may lower the soil pH. Loss of organic matter, removal of soil minerals when crops are harvested and erosion of the surface layer may also cause the reduction of soil pH.

J. C. Tarafdar thank you for the reasonse sir. The site is a forest land with no anthropogenic disturbance ( no farming activities so no application of such chemicals). Is there any other possible factors?

Dear Wati,

If the land is forest land then must be the type of vegetation is coniferous. And coniferous vegetation is acid forming in nature. Kindly check and let me know.

The pH of soil increases as a result of denaturation organic acid at high

temperature where as low soil pH i.e. more acidic during winter because of there is no. denaturation organic acids .

Debabrata Nath thank you for the insight. The site is a natural forest, where there are a mixture of vegetation. Incase the dominant vegetation is not conifers, but suppose lets say, deciduous trees such as oak. What might be the possible factors sir?

Madhukar Baburao Deshmukh thank you for the insightful answer. I will read up some papers on that sir. Regards

Dear Wati,

Say it is deciduous then there will be laterization. And if it is coniferous then there will be podzolization. So kindly have a look about these soil forming processes.

Thank you for the insight sir, I'll definitely look into that.

I have another suggestion. I guess that you are measuring pH in water and that the EC of the suspension is higher in winter than in summer.

Large dilutions with pure water in the lab lower the total ionic strength that applies in the field which produces an artificially igh pH. This is usually prevented by measuring pH in (say) 10 mM CaCl2 solution

Paul Milham thank you for the insightful and excellent suggestions sir. We will try that method