Soil Trace Element Evidence for Horse Corralling during the Copper Age in Northern Kazakhstan

The Copper Age (3700-3100 BCE) Botai horse pastoralists of the Eurasian Steppe region constructed large permanent settlements. Remote sensing imaging of the Krasnyi Yar archaeological site in northern Kazakhstan revealed numerous curvilinear features that could indicate that horses were corralled within the village. Ammonium acetate leachates (NH₄OAc, buffered to pH 8) of modern horse manure from the Krasnyi Yar area are enriched in P and Na as well as other nutrients including sulfur (S), potassium (K), magnesium (Mg), boron (B), manganese (Mn), and zinc (Zn).  A typical horse passes ~20% of its nutrient intake in manure and urine and can generate up to 10 tons of manure a year; a site at which horses were corralled could be expected to show chemical enrichments in the soil reflective of their diet. To investigate this possibility, soil samples were taken along N-S and E-W transects from a depth of 15-25 cm within one of the semicircular enclosures and sequentially leached with NH₄OAc and hydrochloric acid (HCl). Samples within the enclosure show elevated concentrations of P, Na, S, Mg, B, and Zn relative to soils outside of it; potassium is depleted. Unlike P and Na, which are elevated in the modern manure and enclosure samples in both NH₄OAc and HCl leachates, S, Mg, B and Zn are enriched relative to background only in the NH₄OAc leachates. This indicates these elements are being held on exchangeable sites on clay or organic matter, or in soluble secondary salts or sulfates rather than in refractory soil minerals such as silicates. Overall, the geochemical data are consistent with alteration of the Krasnyi Yar enclosure soil by manure additions. Indications of corralling within the Botai village strengthen other evidence that suggest horses were domesticated in the Botai culture by 3400 BCE.