The allelopathic potential of rice straw cv. Giza 178 was evaluated on the germination and seed-ling growth of squash, turnip, lentil wheat, Egyptian berseem and flax. Germination percentage and rate of all studied crop seeds were not affected significantly by aqueous extracts of rice straw, ex-cept for the rate of germination of flax which was delayed by increasing the extract concentration. Shoot length of flax was inhibited by 10.2% with 0.1% dilution, but was stimulated for wheat shoot length by5.6% at undiluted extracts. Seedling length of turnip and flax was stimulated by 46.9& 16.2%, respectively¸ with undiluted extracts. Seed-ling growth response depended on the extract concentration. Squash seedling fresh weight was stimulated by 9.3% at undiluted extract. How-ever all other crop seedling fresh weight was not significantly affected.
Residues from rice straw placed in pots of sand had no significant effect on the emergence per-centage and rate of all studied crops, except for emergence percentage of Egyptian berseem and wheat which was increased and the rate of emer-gence of turnip and lentil which were delayed by increasing residue concentration. The flax emerged seedling shoot length and lentil seedling length were inhibited by 9.6% and 14.3%¸ respec-tively, in the presence of low rice straw residues as compared with control. The fresh weight of turnip, lentil, squash and wheat emerged seedling were stimulated by 3.3%, 8.4%, 22.8% and 26.4%¸ re-spectively¸ at higher residue concentration (1%).
The stimulation effect by undiluted extract, and higher residue concentration from rice straw tissue may contain water-soluble compounds that exert allelopathic effect on the growth of studied crops under controlled environmental and greenhouse conditions, and it may be recommend to incorpo-rate rice straw in the soil at higher concentration under field conditions. However more research is needed to identify these possible allelopathic com-pounds and demonstrate their potential field condi-tions.