Rapid Saturation–Diffusion Method to Determine Cation- and Anion-Exchange Capacities in Soil

Vander Luis Novais Nunes, R. L. Mulvaney

Research output: Contribution to journalArticlepeer-review


Soils have long been recognized for electrostatic retention of anions as well as cations, although this property is usually characterized by measuring cation- but not anion-exchange capacity. A technique is described that determines effective cation- and anion-exchange capacities (CECe and AECe) for a single soil sample. In this technique, 0.5 g of soil is saturated by treatment with 1 or 0.006 M ammonium nitrate (NH4NO3) using a vacuum manifold equipped with disposable syringes, the excess NH4NO3 is removed by leaching with 2-propanol, and sequential diffusions are performed to determine ammonium-nitrogen (NH4+-N) as CECe and nitrate (NO3)-N as AECe. In evaluative studies, complete saturation of cation- and anion-exchange resins was achieved with 1 but not 0.006 M NH4NO3, and neither CECe nor AECe measurements were affected by entrapment of excess saturating reagent, cross-contamination of NO3-N diffused following 15NH4+-N, or interference due to soil organic N. Good agreement was obtained in comparing CEC data collected with 1 M NH4NO3 and ammonium acetate for 10 soils dominated by permanent charge but not for seven highly weathered soils. For all soils studied, both CECe and AECe were significantly reduced by the use of 0.006 M NH4NO3, and the AECe data thereby obtained agreed closely with compulsive exchange measurements using 0.002 M barium chloride. The rapid saturation-diffusion method described measures CECe and AECe when using 1 M NH4NO3, and can also be performed to estimate electrostatic ion retention at a low ionic strength (μ = 0.006) that approximates field conditions.

Original languageEnglish (US)
Pages (from-to)76-91
Number of pages16
JournalCommunications in Soil Science and Plant Analysis
Issue number1
StatePublished - 2021


  • 2-propanol
  • Cation-exchange capacity
  • ammonium nitrate
  • anion-exchange capacity
  • leaching
  • rapid saturation-diffusion method
  • vacuum manifold

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Soil Science


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