Abstract
BackgroundStable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ15N). Animal excrement is known to impact plant δ15N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint.Methodology/Principal FindingsThis paper presents isotopic (δ13C and δ15N) and vital data for maize (Zea mays) fertilized with Peruvian seabird guano under controlled conditions. The level of 15N enrichment in fertilized plants is very large, with δ15N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ15N values ranged between −0.3 and 5.7‰. Intraplant and temporal variability in δ15N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ13C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk.Conclusions/SignificanceThe results presented in this study demonstrate the very large impact of seabird guano on maize δ15N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data from archaeological material.
Highlights
Seabird excrement was arguably the most economically significant organic fertilizer in the world prior to the twentieth century
Conclusions/Significance: The results presented in this study demonstrate the very large impact of seabird guano on maize d15N values
The trade in guano peaked during the middle of the nineteenth century, with 20 million tons being exported to Europe and North America between 1848 and 1875 [2]
Summary
Seabird excrement (guano) was arguably the most economically significant organic fertilizer in the world prior to the twentieth century. The importance of guano as a fertilizer prior to the nineteenth century is less well known, but is mentioned by Spanish chroniclers and in colonial administrative documents [6,7]. On this basis, some have suggested that it may have been of some importance in prehispanic agriculture [8,9]. Animal excrement is known to impact plant d15N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint
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