Synthetic fertilizers and raw or composted livestock manure are typical nitrogen (N) sources in intensive cropping and livestock-farming systems. The distinct N isotope ratios ( 15 N/ 14 N, expressed as δ 15 N) of the N sources make it possible to use the δ 15 N of soil, plant and groundwater samples to trace the N derived from the two N sources in the agricultural landscape. However, N isotope fractionation during N cycling may hamper the usefulness of the δ 15 N technique for tracing N. This paper reviews the changes in the δ 15 N of soil, plant and groundwater samples in the agricultural landscape as affected by synthetic fertilizer and raw or composted manure applications with consideration of the effect of N source and N fractionation during N cycling on variations in δ 15 N. First, this review summarizes the fundamental N isotope fractionation theory with an emphasis on the critical role of nitrification in changing δ 15 N through N loss. Second, the differences in the δ 15 N of synthetic fertilizer and raw or composted manure are discussed with an emphasis on mechanisms that increase δ 15 N in raw or composted manure. Third, the effects of synthetic fertilizer and raw or composted manure applications on the variations of δ 15 N in soil, plant and groundwater samples across different scales of experiments from laboratory to watershed are discussed. We conclude that in spite of N isotope fractionation, the feasibility of the δ 15 N technique in tracing N originated from synthetic fertilizer and raw or composted manure in soil, plant and groundwater in the agricultural landscape can be strengthened when site-specific information on the δ 15 N of N sources as well as the dominant N processes is available. [ABSTRACT FROM AUTHOR]