During nitrification process, protons are released, which reduce the soil pH and results in soil acidification. I am interested in knowing at how much depth these protons can travel down the soil profile.
Nitrogen fertilizers are immediate soluble in water. Therefore, the presence of proton during nitrification is not govern by single factor. The availability of water content, soil types and fertilizers are the predominant factors. However, the production of proton more closely related to the availability of fertilizer at certain depth.
Dear Sajjad
Two hydrogen ions (i.e. H+) (referred to as protons) are released following each nitrification (ammoniacal-N to nitrate-N) process. Nitrification can occur either from applied fertiliser-N (as urea, ammonium sulphate or ammonium nitrate) or even organic fertilisers such as composts or residual soil organic-N or ammoniacal-N (by organic-N mineralising to ammoniacal-N which in turn nitrifies as nitrate-N).
Nitrification is also possible from grazed pasture from animal urine since it has urea which hydrolyses into ammoniacal-N which can nitrify as nitrate-N.
All the above will result in protons or H+ accumulations in soils which will manifest in soil pH reduction or increasing in soil acidity. There has been substantial publication in soil acidity caused by nitrification. Often such acidity tends to be in the top soil (0-150 mm) but can leach down the profile (>300 mm) if the soil acidity is significant or prolonged. A well known correction of soil acidity is regular lime dosing which will remove or neutralise protons in soils.
Kind regards
Selva
Selva Selvarajah Thank you very much Sir for your detailed answer. May I request you for a reference of the statement "Often such acidity tends to be in the top soil (0-150 mm) but can leach down the profile (>300 mm) if the soil acidity is significant or prolonged."
Dear Sajjad
My reference to long term effects of grazing and N fertilisation on soil acidity has been based on numerous papers on soil acidity studies. You will note wherever soil pH is acidic at 0-75 mm the same phenomenon (i.e. acidity) is observed at 75-150 mm (or 0-150 mm vs 150-300 mm, depending on the depth studied by workers) or in deeper profiles. Whilst acidity can leach, the remedy such as lime can also leach to improve soil acidity at deeper profiles. At lower profiles, microbial activities including nitrification is low hence acidity is generated in the top soil profiles such as 0-75 or 0-150 mm. Thus if lower soil profile is found to be acidic, it is dominated by soil acidity changes in the top profiles.
Soil acidity is studied in the context of N fertilisation, grazing, cropping and liming. Soil acidity can be measured by pH and indirectly by Al availability in soil or lack of base saturation. You could find much of the useful references by web search, but ensure you use the correct key words such as "acidity, N fertiliser, soil depth, pH, soil Al & pH, nitrification & soil acidity, grazed pasture and soil acidity etc. etc.".
I have given the following references but not limited to:
https://dl.sciencesocieties.org/publications/aj/pdfs/109/2/706 - this paper has info on N fertilisation effect on soil pH with depth
https://link.springer.com/chapter/10.1007/978-94-011-0221-6_130 - this paper deals with N and K fertiliser application effects on soil pH changes
https://www.researchgate.net/publication/240507272_Soil_acidification_under_clover_pasture - in this paper soil pH decline extending to 300 mm
https://link.springer.com/article/10.1007/BF01049667 - pot trial showing calcium nitrate increasing pH whilst ammonium sulphate decreasing pH, without studying soil depth effect
http://www.agriculture.gov.au/SiteCollectionDocuments/natural-resources/soils/trends-factsheets/vic-practices-grazing.pdf - a different paper on practical implications of grazing on soil acidity in Australia
If you need any further assistance please let me know.
Kind regards
Selva
Dear Selva Selvarajah Thank you very much for such a detailed answer and very useful attachments. I found all the attached articles very informative and they have thoroughly improved my understanding. I appreciate your valuable time.
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