Processes of soil acidification during nitrogen cycling with emphasis on legume based pastures

N. S. Bolan, M. J. Hedley, R. E. White

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325 Citations (Scopus)


In areas that remain unaffected by industrial pollution soil acidification is mainly caused by the release of protons (H+) during the oxidation of carbon (C), sulphur (S) and nitrogen (N) compounds in soils. In this review the processes of H+ ions release during N cycling and its effect on soil acidification are examined. The major processes leading to acidification during N cycling in soils are: (i) the imbalance of cation over anion uptake in the rhizosphere of plants either actively fixing N2 gas or taking up NH4+ ions as the major source of N, (ii) the net nitrification of N derived from fixation or from NH4+ and R-NH2 based fertilizers, and (iii) the removal of plant and animal products containing N derived from the process described in (i) and losses of NO3-N by leaching when the N input form is N2, NH4+ or R-NH2. The uptake of excess cations over anions by plants results in the acidification of the rhizosphere which is a "localized" effect and can be balanced by the release of hydroxyl (OH-) ions during subsequent plant decomposition. Nitrification of fixed N2 or NH4+ and R-NH2 based fertilizers, and loss of N from the soil either by removal of products or by leaching of NO3-N with a companion basic cation, lead to 'permanent' acidification.

Original languageEnglish
Pages (from-to)53-63
Number of pages11
JournalPlant and Soil
Issue number1
Publication statusPublished - Jul 1991
Externally publishedYes


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