STABLE ISOTOPE ANALYSIS FOR TRACING BIOSOLIDS-DERIVED N: AN EXAMPLE FROM CATTLE GRAZING BIOSOLIDS-AMENDED RANGE
Abstract:Stable isotope mixing models can be used to determine the proportion of two isotopically distinct sources in a mixture. Nitrogen in biosolids, highly processed human waste, can be distinguished from natural soil N on the basis of isotopic composition. Information about the relative contribution of N from these two sources is preserved as N moves through the ecosystem. This study was conducted to determine (1) if isotope analysis can effectively be used to trace biosolids-derived N in a desert environment, (2) if cattle, given free choice between biosolids treated and non-treated range, preferred one over the other, and (3) what proportion of plant N is biosolids-derived when plants are grown where biosolids have been applied. In June 1999 biosolids were applied to treated pastures at a rate of 18 dry-Mg ha−1. Two single-choice pastures provided cattle with forage. In one, the entire pasture was treated with biosolids and, in the other, no biosolids were applied. Four additional pastures were free-choice, where half of the pasture was treated and the other half was not treated. Cattle were allowed to graze during 3 trials. Feces, forage, and biosolids samples were collected and analyzed during this experiment. Both C and N isotopes were measured. In the first trial the analysis indicates that in biosolids treated pastures about 22% of the forage N is biosolids-derived. Secondly, cattle given free choice selected about 84% of their forage from the biosolids treated portion of the pasture and 16% from the non-treated portion. This study has demonstrated the usefulness of stable isotope analyses to trace biosolids in these environments. The possibilities for future isotope work in this environment are numerous.
Document Type: Research Article
Publication date: January 1, 2002
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