A study was carried out to investigate the N derived from the incorporation of pea (Pisum sativum L) and red clover (Trifolium prasente L) residues into soil-crop systems by employing 15N-labelling techniques. It consisted of two experiments, namely: incorporation of pea (1st experiment) and red clover (2ndexperiment) residues into soil. The treatments applied were shoot residue (SR1–SR8), root residues (RR1–RR8) and non-residues (NR1–NR8) incorporation into soil. Four pots of each treatment (SR1–SR4; RR1–RR4; and NR1–NR4) were sampled 21 days after residues incorporation (21 DARI) into soil. Concurrently, the remaining pots (SR5–SR8; RR5-RR8; and NR5–NR8) were also sampled, but these then were allowed to grow 35 and 28 days further for another sampling, respectively, both for the 1st and 2nd experiments. The results showed that a certain amount of N had been released both from shoot and root of pea and clover residues and derived to ryegrass (indicator crop). The N shoot and root of ryegrass derived from pea residues decreased from the 1st to the 2nd samplings. While the derived-N from red clover residues in the shoot and root of ryegrass increased and decreased from the 1st to the 2ndsampling, respectively.