Synthetic fertilizer and livestock manure differently affect δ15N in the agricultural landscape: A review

•Synthetic fertilizers (SF) and livestock manure (LM) are typical N sources.•The δ15N of soil, plant, water samples is affected by both N source and loss.•Application of 15N-depleted SF decreases δ15N in soil, plant, water samples.•Application of 15N-enriched LM increases δ15N in soil, plant, water samples.