The soil type I have noted this effect on is "Hutton" Orthox, Ferralitic R.
4 Samples each sampling pH shift =
pH 6.9 June 2015
pH 5.9 September 2015
Location Uplands East Coast South Africa
pH shifts of this magnitude are common in rice paddy soils
You may refer to the attached paper for an answer. With best wishes-
I agree with you Paul , especially when soil is ferralitic in nature .
Surely pH changes in most of the soils as temperature changes which effect the availability of of nutrients. Pl. get help from following papers.
Hi Phillip, interesting observation. Are these flooded soils or is there significant wintertime water logging? If so production of ferric hydroxide will generate considerable acidity. Cheers Clint
Clinton, the climate is summer wet, winter dry and yes the soil does become very muddy. The striking soil colour is another strong indicator as to what is happening, it is bright Red/Brown Strong chroma. Can you please clarify your comment? " production of ferric hydroxide will generate considerable acidity" I have always thought that any Hydroxide containing compound was Alkaline. The wonder of soil science is that it often gives unexpected surprises.
Hi Philip,
It is my understanding that the oxidation of reduced iron (Fe2+) to Fe3+ in the presence of water and oxygen produces considerable acidity. So reduced iron due to water logging during your wet season that is subsequently oxidized (often due rhizosphere O2 pumping) can theoretically produce 8 moles of protons for every 4 moles of ferric hydroxide. Yes I agree it's kinda counter intuitive but has been well documented especially in ferralitic soils. The reference of Begg (Root-induced iron oxidation and pH changes in the lowland rice rhizosphere BY C. B. M. BEGG et al) is one such ref although there are plenty more out there. Pretty fascinating stuff infded. Regards Clint
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