Base Cations (Ca,Mg,K,Na)

Inputs of base cations in the precipitation were relatively low during this period. Concentrations of base cations increased in the canopy throughfall in spite of the fact that no foliage remained on the trees during this time. Concentrations of the macro-nutrients Ca, Mg, and K were highest in the A horizon and showed a progressive decrease in the AB and Bt horizons. This pattern of high concentrations in the upper soil horizons and decreasing concentrations with depth are characteristic of elements which are strongly affected by nutrient cycling. Cycling of essential nutrients maintains an abundant supply of nutrients for incorporation into new biomass while at the same time limiting nutrient losses from the soil profile. Elements which are available in excess of the plant requirement are leached from the soil profile in quantities greater than elements which are in short supply. An example of this is shown for the nonessential element, sodium. Sodium concentrations tend to increase with increasing depth resulting in considerable loss of Na from the rooting zone.

Soil solution concentrations of Ca and K were attenuated in the A and AB horizons following tree removal. Concentrations in the cut plots were approximately midway between those in the oak canopy and grassland soil plots. This indicates that concentrations of Ca and K rapidly decrease toward those of grassland soils following tree removal. Concentrations of Ca and K in the Bt horizon were similar for all three treatments indicating that there was only a small increase in leaching losses from the upper soil profile due to the effects of tree removal. In contrast, concentrations of Mg were nearly identical in the oak canopy and cut plot soil solutions. Sodium was not affected by tree removal and soil solution concentrations were similar for all three treatments.