Changes in extractability of iron, aluminum and silicon and dispersibility by storage of california forest soils

Abstract

Abstract The effect of long‐term laboratory storage on the extractability of pedogenic organic, Fe, Al and Si‐bearing phases and soil dispersibility in two California forest soils was investigated. Storage of A and BC‐horizon samples generally resulted in significant decreases in oxalate and pyrophosphate‐extractable Al and Fe. Aluminum and Fe extractability by pyrophosphate generally decreased more than oxalate extractability, resulting in apparent increases in the quantities Alo‐Alp and Feo‐Fep. Effects of storage on Si extractability were variable. Extraction of organic carbon from A‐horizon soil increased through storage while extractability decreased in BC‐horizon samples. Storage decreased the chemical dispersibility of A and BC‐horizon soil, thus implying an increase in aggregate stability. Ultrasonification treatment prior to chemical dispersion of field‐fresh and lab‐stored samples had little effect on particle size distribution. Decreases in pedogenic organic, Al, Fe and Si extractability can be empirically related to apparent increases in aggregate stability, though the specific mechanisms by which aggregates are stabilized through drying are unclear.