The archaeological value of soil phosphate prospections in artificially fertilized areas – a case study in the area of Sievern (county of Cuxhaven)

Abstract

For a reassessment of a soil phosphate prospection from the 1990s new phosphate analyses were carried out in the area of Sievern (county of Cuxhaven) in 2011-2012. Three transects of soil profiles were sampled for the determination of slightly and easily soluble phosphates with 12.1- and with 0.1-molar hydrochloric acid. It was verified that higher phosphate contents occur in the west and low contents in the east of the study area. Except for few spots highly enriched with phosphate, the local soils mostly show no to mediocre increases not indicating extensive pre-medieval settlement over a vast area. Furthermore, the measured phosphate amounts include on average 47 % of easily soluble phosphates probably stemming from modern fertilization. Therefore phosphate contents in the agriculturally intensively used area of Sievern are only of reduced archaeological significance and they demand a modified analytic procedure. By sampling soil profiles in vertical steps of 5 cm it was furthermore shown, that in the local sandy soils phosphates can be translocated to depths of 40-80 cm. The sampling underneath the plough layer carried out in the 1990s may thus have led to investigating soil horizons heavily enriched with modern phosphates. The conclusions drawn from these data therefore have to be seen critically.