Causes of soil acidification: a summary

. A review of recent data shows that (i) dissolved CO 2 has its greatest acidifying effect in soils with pH values above about 6.5, (ii) fertilizers containing NH −1 + ions or urea will acidify soil whether the ions are taken up directly by plants or are first nitrified, (iii) oxidation of nitrogen and sulphur in soil organic matter causes acidification especially after deforestation, and (iv) the acidifying effect of rainfall and dry deposition is due to sulphuric and nitric acids, SO 2 and NH −1 + ions. A table is given showing the order of magnitude of each source of acidification.