Effect of compost enriched with N and L-tryptophan on soil and maize Rizwan Ahmad, Azeem Khalid, Muhammad Arshad, Zahir A. Zahir and Tariq Mahmood Agron. Sustain. Dev., 28 2 (2008) 299-305 Published online: 15 March 2008 DOI: 10.1051/agro:2007058