The Allelopathic Potential Effect of Winter Crops on Biochemical Constituents and Productivity of Cotton

llelopathy is an important mechanism of plant interference mediated by the release of plant-produced secondary metabolites or decomposition products of microbes to the aerial or soil environment. Its potential effect (promote or inhibit) of onion, clover, barley and garlic soil residues on germination percentage, seedling growth, leaves chemical constituents, yield components and fiber properties of cotton Giza 97 cultivar was studied by using seed-after-seed protocol. The allelopathic potential winter crop residues significantly affected all study parameters. Sowing cotton after onion, clover and garlic residues enhanced seed germination, seedling growth, metabolic activities yield components and fiber properties in 2021 and 2022 seasons compared with control. These might be related to the presence of promoter substances (allelochemicals) improving cotton germination, growth and development. Conversely, cotton planted after barley residues showed a reduction in germination, seedling growth, leaves chemical constituents and yield in both seasons compared to control. These might be attributed to the high concentration of phenols and flavonoids in barley residues causing repression of germination, growth and development of cotton. Onion residues achieved the best positive effect (above the control) on cotton germination (4.99 and 3.98%), seedling fresh weight (18.21 and 16.68%), boll weight (14.01 and 19.59%) and seed cotton yield (32.26 and 43.01%), respectively, in both seasons compared to fallow plants. Barley residues achieved the lowest negative results (below the control) for cotton germination (9.42 and 13.34%), seedling fresh weight (13.6 and 16.46%), boll weight (8.28 and 6.75%) and seed cotton yield (13.73 and 13.22%), respectively, in both seasons compared to fallow plants.