Variations in crop grain and soil N isotope composition (d¹⁵N) as affected by liquid hog manure (d¹⁵N of total N was +5.1‰), solid cattle manure (+7.9‰) and chemical fertilizer (+0.7‰ for urea and -1.9‰ for ammonium phosphate) applications, and control (no fertilizer application) were examined through a 4-year crop rotation under field conditions. Canola (Brassica napus), hulless barley (Hordeum vulgare), wheat (Triticum aestivum), and canola were grown sequentially from 2000 (year 1) to 2003 (year 4). From year 2, hog manure or chemical fertilizers, but not cattle manure, treatments increased grain N concentrations over control. Grain d¹⁵N (+0.3 to +2.5‰) of crops applied with chemical fertilizers was lower than those in the other treatments, reflecting the effects of the ¹⁵N-depleted N source, while the manure treatments tended to increase grain d¹⁵N. The higher grain d¹⁵N of crops applied with hog manure (+5.6 to +8.4‰) than those applied with cattle manure (+2.2 to +4.1‰) reflected the higher N availability of liquid hog manure (up to 70% as ammonium) than solid cattle manure (99% organic N) and higher potentials for ammonia volatilization loss in hog manure rather than differences in manure d¹⁵Nsignatures. Soil total and extractable N concentrations and d¹⁵Ntended to vary with the application of N sources with different N isotope composition and availability. Our study expanded the application of the d¹⁵N technique for detecting N source (organic vs chemical) effects on N isotopic composition to field conditions and across a 4-year rotation, and revealed that N availability played a greater role than the d¹⁵N signature of N sources in determining crop d¹⁵N.