USE OF A SOIL CHRONOSEQUENCE TO CALIBRATE SOXHLET GENERATED CHRONOFUNCTIONS

A calcium-bound phosphate (PCa) chronofunction from a Vancouver Island soil chronosequence was compared mathematically with a chronofunction produced by leaching parent materials from the soil chronosequence with 0.3 M acetic acid for up to 24 wk in modified soxhlet extractors. The equivalent of approximately 13 yr of PCa weathering in the surface 10 cm of the chronosequence soils was achieved by one week of leaching in the soxhlets. After 24 wk of soxhlet leaching, the parent material samples lost approximately 20% of their original 220 g weight and resembled Ae horizon samples from the soil chronosequence. Equations derived from the change in elemental composition of the soxhlet-leached parent material samples were used with the elemental composition of the top 10 cm of the youngest soil (127 yr) in the chronosequence to predict the elemental composition of the top 10 cm of the oldest soil in the chronosequence (550 yr). The predictive equations were useful for elements such as Ca, Na, K, Al, Si and PCa, whereas the amount of Mg and Fe remaining in the soil chronosequence was overestimated, due to the inability of the acetic acid solution to attack ferro-magnesian minerals. An equation relating the weight of soil residues to soxhlet leaching time predicted that the chronosequence soils would experience a lowering landscape rate of 0.05 mm yr−1. The soxhlet leaching and field-time calibration technique described is considered by the authors to be useful for other applications, such as predicting loss of soil buffering constituents due to acid rain or predicting rates of release of elements from contaminated soils. Key words: Soil chronofunctions, soil chronosequence, soxhlet weathering, leaching