Thermophilic microorganisms in arable land around medieval archaeological sites in Northern Caucasus, Russia: Novel evidence of past manuring practices: Chernysheva et al.

Thermophilic microorganisms in the soils of medieval cultivated fields located within the Kislovodsk Basin (Northern Caucasus, Russia) were selected as a means for the reconstruction of manuring practices. Thermophilic bacteria are specific groups of microorganisms that develop in manure during the composting process when temperatures reach 60-70 degrees C. The abundance of this type of bacteria in soils depends greatly on the intensity of farming practices. In medieval cultivated soils (Alanic Culture, A.D. 500-800), high numbers of thermophilic bacteria were observed, indicating the long-term use of manure. In arable lands near Alanic settlements, the abundance of thermophilic bacteria decreased significantly with distance from the sites. The highest abundance of thermophilic bacteria was observed in the 500 m zone adjacent to the sites. Moreover, the highest concentration of thermophilic microorganisms was found in the soil within an Alanic corral. We suggest that dung accumulated in the paddock for a long time. Abundance of thermophilic microorganisms at archaeological sites could be used as a new indicator of the application of decomposed manure to ancient and medieval arable soils.