Allelopathic Potential of Three Sunflower Cultivars on Some Successive Crops and Companion Weeds

Abstract

Field Trail was carried out in Alhamdhia Research Station of College of Agriculture / University of Anbar during the agricultural season (2021 - 2022). Allelopathic potential of residue parts for three sunflower cultivars Helianthus annuus L. These were Sakha, Akmar and Ishaqi were evaluated under open field conditions against weed flora associated with the proposed crops; wheat, broad bean and flax, the crops were cultivated usually after sunflower crop as successive crops. After getting seed from sunflower , plant parts were chopped and incorporated with field soil using a rotavator. The results showed the following: Highest content of total phenolic compounds observed in the field mixed by Sakha cultivar at 4th week after mixing recorded (1.48mg g)^(-1) while the phenolic content in control (soil without residues) recorded lowest content in most of the weeks measuring. Studied soil properties indicated that the sunflower residues enhanced soil properties by increasing the essential nutrients; NPK. Moreover, organic matter and C/ N ratio also increased from 44 to 143% regarding the variations between the time after mixing the residues and sunflower cultivar . Weed density per m2 at 30 and 60 days after cultivation significantly reduced by residues of the three sunflower cultivars . Furthermore, all traits of the sunflower residues showed desired reduction against weed dry matter. However, lowest dry matter average was observed with weed associated with wheat crop. There was also a discrepancy between weed dry matter growing in control treatments, which indicates that crop species significantly impact the growth of weed growing with it and ranged according to its severity. Data of crop injury symptoms in successive crops effected by sunflower residues showed changing green color of wheat plants to a pale green color as a result of the damage that occurred to the plants from allelopathic stress. Regarding broad bean crop, the injury score in this crop affected by sunflower residues behaved same as wheat plants except for slight dwarfing, but the general condition of the plant is rather good. On the contrary, flax plants showed more sensitivity to sunflower residues in addition to yellowing, damage exceeded dwarfing and burning of the edges of some leaves were seen. Sunflower resides improved growth properties of wheat crop, thus increasing the grain yield average 22.75, 22.6 and 19% for Sakha, Akmar and Ishaqi cultivars. Allelopathic potential of sunflower residues appeared inversely on developing the growth of bean and flax crops, which did not achieve an increase in the final yield despite the supply of soil with essential growth requirements.