Efficacy of irrigation intervals and chemical weed control on optimizing bulb yield and quality of onion (Allium cepa L.)

: Two field experiments were carried out at the village ten, Abu Humus, El-Beheira Governorate, Egypt, during the two successive seasons 2016/2017 and 2017/2018, to evaluate the effect of three types of herbicide and three irrigation intervals on productivity and quality of onion cultivar (Giza Red). The experiments were designed as split plot in randomized complete block design with three replications. Irrigation intervals – (I 1 ) 20 days, (I 2 ) 30 days, and (I 3 ) 40 days – were assigned to the main plots. Herbicides treatments – (H 1 ) Control, (H 2 ) Fluazifop-p, (H 3 ) Oxyfluorfen, and (H 4 ) Clethodium – were distributed randomly in sub-plots. The results revealed that the interaction between herbicide and irrigation intervals had significant effects on productivity and quality of onion (Giza Red) cultivar in both seasons. Maximum onion bulbs yield (14.06 and 14.29 ton/fed) was recorded at (I 3 with H 3 ) treatments in first and second seasons, respectively. (I 2 with H 3 ) led to increase onion harvest index values. The highest value of carbohydrates percentage and total soluble solids (TSS) obtained at {I 3 and H 2 }. Herbicides residues in dry onions bulbs under all treatments were found well below the maximum residue limit set by World Health Organization (WHO)/Food and Agriculture Organization (FAO) (0.05 mg/kg). In conclusion, the interaction of Oxyfluorfen herbicide and irrigation interval 40 days could be used to improve fresh and dry bulb yield (ton/fed) of onion cultivar, harvest index and water use efficiency (WUE). The treatment of {I 3 (40 days) with H 2 (Fluazifop-p)} could be used to enhance bulb diameter (cm) after harvest, TSS and the percentage of carbohydrates.