Allelopathic effect of different rates and ages of sunflower plant (Helianthus annuus L.) residues on emergence and growth of corn (Zea mays L.)

Utitization of plant residues has led to identification of natural methods of crop protection. One of such method is using the knowledge of allelopathy. A field study was conducted to determine the response of corn to different rates and ages of sunflower residues in Sari, Iran, using a randomized complete block design with seven treatments and four replications. Treatments included The age of plant residues (6, 8, and 10 week-old), plant residue rates (8 and 16% soil weight), and control (no plant residue). Seedling emergence (two weeks after planting), plant height and dry weight of corn (two, four, and six weeks after planting) and final plant height and dry weight and grain yield of corn plant were measured. Results showed that seedling emergence, height, and dry weight were reduced in comparison with control. Increasing the age of residues did not significantly affect on these traits for 6 and 8 weeks old residues, but 10 weeks old residue reduced all measured traits. Residues rate did not significantly affect these traits. The most reduction in final plant height and dry weight were observed in older residue (10 weeks old) mixed with soil treatment (22 and 52%, respectively). In this study residues from older plants found to be more phytotoxic.