Influence of seabird guano and camelid dung fertilization on the nitrogen isotopic composition of field-grown maize (Zea mays)

Organic fertilizers have the capacity to alter the nitrogen isotopic composition of plants. Camelid dung and seabird guano are two potentially important fertilizers in the agricultural systems of western South America, particularly Peru and Chile. This paper presents isotopic data (δ¹³C and δ¹⁵N) from field grown plants (maize, Zea mays) fertilized with the following four treatments: CO (control, no fertilizer applied), AS (ammonium sulfate, a chemical fertilizer), DU (camelid dung), and SG (seabird guano). Plants were grown in experimental plots in the Virú Valley, northern Peru. Plants fertilized with the chemical fertilizer presented very similar isotopic compositions compared to the control. Conversely, the camelid dung fertilized plants were characterized by higher δ¹⁵N values compared to the control plants (by 1.8 to 4.2‰ depending on the plant part). The seabird guano fertilized plants were greatly enriched in ¹⁵N in comparison to the control plants (by 11.3 to 20.0‰). The results of this study have important implications for the reconstruction of human diet using isotopic data derived from bone collagen and related tissues, particularly in the prehispanic Andes, but also in Europe and North America during the 19th century, when Peruvian seabird guano was used extensively. Specifically, the interpretation of the relative contributions of plant and animal protein to the diet on the basis of bulk isotopic compositions of bone collagen (or similar tissues) may be confounded by camelid dung fertilization if the carbon isotopic compositions of the two sources are similar. Likewise, the interpretation of the relative contributions of maize and marine protein may be confounded by seabird guano fertilization.     

A pottery workshop with flint tools on blades knapped with copper at Nausharo (Indus civilisation, ca. 2500 BC)

Twenty years after its discovery, the pottery workshop of Nausharo (province of Baluchistan, Pakistan), which yielded a series of knapped stone tools in association with unbaked sherds and clay waste, is still of unique importance in Asian protohistorical studies. The types of pottery production (sandy marl fabrics) identified in this workshop, which is dated to ca. 2500 BC, correspond to the majority of the domestic pottery discovered at the site during the first two phases of the Indus Civilisation. The flint blades discovered in the workshop were made from exotic flint, coming from zones close to the great Indus sites such as Mohenjo-Daro and Chanhu-Daro. This is also the origin of a small amount of the pottery (micaceous fabrics) found at Nausharo in domestic contexts, e.g. Black-Slipped-Jars. The butts of the blades display features characteristic of pressure detachment with a copper pressure point. Gloss and microwear traces (polish) testify to the blades' having been used for finishing the clay vessels: for actual finishing (trimming) while they were being turned on a wheel, and possibly also for scraping by hand. Both of these operations are distinctly attested to by the presence in the workshop of two different types of clay shavings.