Phosphate Fractionation of Soils at Agroal, Portugal

Abstract

Eidt (1973, 1977, 1984a) suggested that the analysis of soil phosphate fractions (I-III) could be used to identify land-use areas on archaeological sites as well as serve as a relative-dating technique. He noted that the total inorganic phosphate value (I + II + III) reflects the type and intensity of land-use practice, and he hypothesized that the ratio of Fraction II/I correlates with the time elapsed since soil enrichment. A test of these propositions was carried out in conjunction with the excavations at the settlement of Agroal (Portugal), which was occupied during the Bronze Age (2000-1000 B.C.) and Middle Ages (A.D. 1300-1640). Samples were taken from all archaeological levels of the site as well from soils with known land-use histories in the area of Agroal. Results of this study support Eidt"s two principal hypotheses. First, there was a strong correspondence in the control soils between total phosphate values and the nature of land-use activities. Second, the ratio of Fraction II/I in the archaeological samples did, in fact, correlate with the relative age of the associated artifacts. A model of the site"s land-use history, based on the total inorganic phosphate and the Fraction II/I values, suggests a significant alteration and degradation of the soil landscape during the Bronze Age, as a consequence of agriculture, herding, and refuse disposal, followed by less-intensive use during the Middle Ages.