such as lignin, polyphenols and cellulose, similar to fresh materials of S. grandiflora in this study, can cause N priming. For example, Azam et al. 1993 found that tops of vetch Vicia villosa Roth. 47 and 55 g kg–1 of N and lignin, respectively applied to soil with low native N mineralization resulted in higher N priming than soybean tops 24 and 80 g kg–1 of N and lignin, respectively. However, these workers found less N priming, i.e., 4-5% of N initially applied, than this study. A larger N priming was reported by Ehaliotis et al. 1998 who found 38% N recovery from maize residues by maize plants when high quality residue of beans Phaseolus vulgaris 44 and 47 g kg–1 of N and lignin, respectively was applied in a sandy soil. Although our data did point out to the occurrence of the N priming effect, the large effect found needs further investigation.