Re: [DIYbio] Barcoding of wheat

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0053763
"The second potentially significant source-related cause of plant δ¹⁵N variation is the uptake of fertilizer-derived N by plants. Animal fertilizers are characterized by extremely variable δ¹⁵N values depending on the relative proportions of N-bearing species in the fertilizer (e.g. urea, uric acid, ammonium, organic matter) [143]. Manures consisting primarily of solid waste derived from terrestrial herbivores tend to have δ¹⁵N values between 2 and 8 ‰ [144], while those that contain a mix of solid and liquid waste (slurry fertilizers) tend to have higher δ¹⁵N values, often between 6 and 15 ‰ [145], [146]. The highest δ¹⁵N values for animal fertilizers (>25 ‰) have been recorded for seabird guano [143], [147], which consists primarily of uric acid and is subject to significant NH₄⁺ volatilization. The addition of animal fertilizer N to the soil therefore adds an N source with an isotopic composition that is usually enriched in ¹⁵N relative to endogenous soil N. This results in higher δ¹⁵N values for plants growing in soils fertilized with animal waste than those plants growing in unfertilized soil or soils fertilized with chemical fertilizers [143], [145]–[147]."