The role of calcium in buffering soils

Abstract. Calcium is the soluble cation that occurs in largest amount in most soils. It does not take part directly in the proton transfer reactions involved in pH-buffering, but it provides the cation charge balance for these reactions. It is also the complementary cation in formulations of chemical potential for many other ions in soils. The presence of free calcium carbonate in calcareous soils. The presence of free calcium carbonate in calcareous soils ensures a very high soil buffer capacity; d AB/ d pH ? 1000 Eq. m^?3.
In acid mineral soils, dissolution and precipitation of aluminium ions contribute to the buffering processes, but most of the buffering in non-calcareous soils is caused by specific ion adsorption at variable-charge sites, in particular those associated with the dissociation of humus acids. Typical buffer capacity values of non-calcareous soils vary from 10 Eq. m^?3 for sandy soils to 100 Eq. m^?3 for peats. The pH changes associated with buffering are produced by leaching of calcium from soil, or by adding calcium to soil in liming materials.