A medieval hillfort as an island of extraordinary fertile Archaeological Dark Earth soil in the Czech Republic

Abstract

Archaeological Dark Earth soil is a category of archaeological anthrosols that has gained much attention because it exhibits higher nutrient content and organic matter stocks and a characteristic dark colour, and enables higher crop yields in comparison to neighbouring soil. However, much is unknown about the chemical properties of Archaeological Dark Earth soils in Central Europe. Therefore, we studied a European Dark Earth (EDE) soil, a type of Archaeological Dark Earth soil, in the territory of the early medieval Dřevíč hillfort, Czech Republic, aiming to compare the chemical properties of EDE with a control soil unaffected by settlement activities. The black colour of EDE soil contrasted highly with the light grey Cambisol of the control. Soil reaction and total element contents (N, P, Ca, Mn, Fe, Al, Cu, Zn, Sr and Rb) were substantially larger in the EDE soil compared with the control and vice versa in the case of the C/N ratio. Also, the content of plant‐available (Mehlich III) P, Ca, K and Mg was larger in the EDE soil than the control. In contrast to Ca, plant‐available and total P and K were not well correlated. Total element contents are highly suitable for geoarchaeological purposes as enrichment factors can be easily calculated. The increased contents of these elements, together with pieces of charcoal visible in the EDE soil, indicate the deposition of organic waste and biomass ash during the existence of the hillfort. Thus, medieval hillforts can represent extraordinary nutrient‐rich islands in the cultural landscape of Central Europe. The chemical signatures generated by past settlement activities are so intense that they cannot easily be masked by short‐term intensive application of mineral fertilizers. Highlights Settlement activities increased soil pH and the content of anthropogenic elements. Enrichment by P, Ca, Mn, Fe, Al, Zn, Cu, Sr and Rb may indicate settlement activities. Analysis of total element contents is suitable for geoarchaeological purposes. Application of mineral fertilizers cannot easily mask signatures of medieval settlement activities.

Response to Referee Comments

“…Thus, ABEs can hardly develop in semi-arid and arid regions because of the high decomposition rate of accumulated organic matter. The depth of the ABE C10 horizon normally ranges from 0.4 to 0.8 m and can extend up to 1m or more (Courty et al, 1989;Macphail et al, 2003), with increasing depth indicating increasing longevity and intensity of settlement activities. Archaeological black earth soils have been studied by many authors (Runge, 1973;Mücher et al, 1990;van Smeerdijk et al, 1995) but were previously limited to visual descriptions of different organic and inorganic inclusions, archaeological features, artifacts, and post-depositional modifications.…”

“…Statistical modeling indicates that more than 150 000 km2 representing 3.2% of the Amazon forest may harbor Dark Earth sites (McMichael et al, 2014). Amazonian Dark Earth soil is most widely studied in Brazil where they occupy relatively large areas with thick altered soil mantles and higher chemical fertility than the surrounding soils not affected by anthropogenic activities (Corrêa, 2007). These sites are known by designations such as black earth (Terra preta), Indian black earth (Terra preta de Indio), anthropogenic black earth (Terra preta antropogenica), and archaeological black earth (Terra preta arqueologica) collectively termed as Amazonian Dark Earths .…”

“…Similar enrichment was obtained for two Terra preta sites in Santarém, Pará state, Brazil, where the contents of total P (366 -460 mg kg-1), Zn (21 -26 mg kg-1), and Mn (25 -32 mg kg-1) was significantly higher in comparison to respective surrounding soils of 54-772 mg kg-1 P, 2 -4 mg kg-1 Zn, and 3 -5 mg kg-1 Mn (WinklerPrins and Falcão, 2010)). Some authors have worked on the chemical content of fragmented potteries found in the Terra preta in the Amazon Basin (Da Costa et al, 2011;Costa et al, 2013). Most of these studies revealed that areas with the highest density of pottery fragments coincide with the highest contents of elements such as Zn, Cu, Mn, Ba, and Sr.…”

“…The physical description of EDE usually divides the depth of the soil into four distinct horizons with the upper horizon mostly made of midden materials in the form of charcoal, shell, bone, plaster, bricks, etc. (Table 1; Courty et al, 1989). Furthermore, Courty et al (1989), categorized EDE from their studies in London into two stratigraphic units; the C19 lower 'pale Dark Earth' unit and the upper 'Dark Earth' unit.…”

“…The availability of P and other elements are from the decomposition of plant materials, excrements, urine, ashes, bones or fish bones, and charcoal. Courty et al (1989) reported an extremely high content of total P between 1.6 to 2.6% in London impacted by bone, feces, or plant decomposition. Nicosia et al (2012) in using Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS) in Dark Earth in Florence, Italy re-…”