Laboratory Methods for Characterization of Peat Materials

Abstract

Organic soils have characteristics that distinguish them markedly from mineral soils. The analytical procedures used for their characterization and classification are relatively recent. Not many organic soils in the world have been analyzed by the methods of the USDA Soil Taxonomy. These methods were originally developed on soils occurring in environments very different from that of the Guayana Highlands. Consequently, adjustments of the analytical procedures were necessary. This chapter first highlights the specificity of organic soils in general, as their characterization and taxonomic classification require the use of criteria and laboratory methods different from those applied to mineral soils. Then, the testing of existing procedures on selected organic soils from a variety of settings in Venezuela is described and discussed. Finally, the application of the calibrated procedures to the Guayana Highland peats is addressed. Soil pits were dug until the bedrock or, in deeper soils, to 150 cm depth. Field sampling faced several limitations that made it difficult to collect truly undisturbed samples, especially in folic and fibric layers, because of high water table and water saturation of the peats, possible contamination of deeper layers by mobilization of chemical and physical constituents from upper layers, and pit wall collapse. Field moisture and bulk density were obtained by oven drying 100 mL of field-moist soil. Rubbed and unrubbed fiber treatments were applied. Organic matter was determined by loss on ignition and by Walkley–Black. The pH in water was measured on field-moist samples and on air-dry fine-ground soil material. The determination of the exchangeable cations and available phosphorus (by Olsen and Bray1 methods) was performed in triplicates on air-dry fine-ground material and on field-moist material with similar dry matter contents.