Robertson, G. Philip; Sollins, Phillip; Ellis, Boyd G.; Lajtha, Kate. 1999. Exchangeable ions, pH, and cation exchange capacity. In: Robertson, G. Philip; Coleman, David C.; Bledsoe, Caroline S.; Sollins, Phillip, eds. Standard soil methods for long-term ecological research. New York, NY: Oxford University Press: 106-114.
AImost all nutrients taken up by plants and microbes are taken up in their ionic form from the soil solution, and knowledge of the size and composition of the soil solution, together with knowledge of nutrient turnover rates, can provide valuable insight into soil nutrient availability and into other biogeochemical processes such as rates of weathering and leaching losses. While nutrient pool size per se can be a poor indicator of availability, changes in pool sizes can indicate changes in ecosystem processes that bear closer examination. Moreover, in all soils the potential for significant hydrologic loss of mobile nutrients is directly related tothe size of the exchangeable nutrient pool and the proportion in solution at any given time.
In this chapter we present standard methods for the extraction of the major cations and anions from soil, the measurement of exchangeable acidity and soil pH, and cation exchange capacity. Methods for the extraction of dissolved-only nutrients (those ions only in the solution phase as opposed to total exchangeable nutrients that have both solution and surface adsorbed phases) are provided elsewhere (see Chapter 9, this volume), as are methods for available phosphorus (see Chapter7, this volume) and dissolved organic nitrogen and carbon (see Chapter 5, this volume).