Nitrogen Isotope Compositions of Synthetic Fertilizer, Raw Livestock Manure Slurry, and Composted Livestock Manure

To investigate the difference in N isotope ratio ( 15 N/ 14 N, expressed as δ 15 N) among N sources (synthetic fertilizer, livestock manure, and manure compost), eight synthetic fertilizer, four livestock manure, and thirty-seven compost samples were collected and analyzed for δ 15 N. The mean δ 15 N values of N sources were -1.5 ± 0.5‰ (range: -3.9 to +0.5‰) for synthetic fertilizer, +6.3 ± 0.4‰ (+5.3 to +7.2‰) for manure, and +16.0 ± 0.4‰ (+9.3 to +20.9‰) for compost. The lower δ 15 N of synthetic fertilizer was attributed to its N source, atmospheric N2 of which δ 15 N is 0‰. Meanwhile, more 15 N-enrichment of compost than manure was assumed to be resulted from N isotopic fractionation (faster loss of 14 N-bearing compound than 15 N) associated with N loss particularly via NH3 volatilization during composting. Therefore, our study shows that δ15N values could successfully serve in discriminating two major N sources (synthetic fertilizer and compost) in agricultural system.