Soil cation-exchange capacity (CEC) is often determined by NH4 saturation, using a 1 M solution of NH4C2H 3O2 at pH 7. A study was conducted to ascertain whether this determination can be performed by employing a simple diffusion technique previously developed for direct inorganic-N analysis of soils. Values obtained for 10 diverse Illinois surface soils following overnight NH4 saturation were correlated very highly with CEC data collected for the same samples on the basis of NH4 analyses by steam distillation (r = 0.999, P < 0.001) or colorimetry (r = 0.999, P < 0.001), and also with data obtained by summing atomic absorption measurements of calcium (Ca), magnesium (Mg), and potassium (K) displaced during NH4 saturation (r = 0.811, P < 0.01). As a much more rapid and convenient alternative to existing methods for preparation of NH4-saturated soil, a simple saturation technique was developed whereby 0.500 g of soil was leached under vacuum with 15 mL of 1 M NH4C2H3O2 (pH 7) in a 10-mL disposable syringe containing a stainless-steel frit, and then with 30mL of 2-propanol. After drying for a few minutes, the soil sample was transferred to a 473-mL (1-pint) wide-mouth Mason jar, treated with 10mL of 2 M KCl, and analyzed for exchangeable NH4 by diffusion with MgO for 1.75 h at 45-50°C on a hot plate. Except for a calcareous soil, CEC measurements by the rapid saturation-diffusion approach did not differ significantly (P < 0.05) from diffusion data involving overnight NH 4 saturation. This approach allows CEC determinations to be accomplished in a few hours instead of days, and will be especially useful for routine soil characterization and testing.
- Cation-exchange capacity
- Soil analysis