We investigated whether organic compost and urea produce specific delta N-15 signals in soil and tomato plants (Lycopersicon esculentum Mill. cv. Pinguan) under intensive management in greenhouse conditions. Urea (U) and compost (C) were applied to the soil separately (U or C) or together (CU) during crop growth to give a total application rate of N 800 kg ha(-1) in all three treatments. Plant parts (roots, leaves, stems and fruits) and soil samples were taken at the seedling, fruit expansion and mature stages. The results indicate that all three fertilization practices produced significant delta N-15 differences in soil and plant tissues. The concentration of delta N-15 in plant tissues was in the order C > CU > U, and delta N-15 in soil followed the trend C > CU congruent to U. At maturity the delta N-15 values ill plants averaged 17.8+/-0.4 parts per thousand, 10.0+/-0.6 parts per thousand, and 5.9+/-0.4 parts per thousand (n = 3) under C, CU, and U treatments, indicating that delta N-15 of plant and its tissues can reflect compost or chemical N source in long-term fertilizer history. Although we found that plant assimilation N, reallocation N, plant age and N loss in the soil exerted effects on the N-15 discrimination of the different plant parts during growth, the two amendments (urea and compost) influenced the final tissue delta N-15 of the plants. Moreover, it was possible to distinguish between crops to which urea or compost was applied on the basis of the delta N-15 of the plant parts and it was a good method to distinguish organic and commercial food.