This study explores the potential role of combined biochar and compost amendments, along with cobalt spraying on the growth and yield of onion grown on soil with an EC value of 7.42 dSm^-1. A field trial was conducted with the main treatments being soil amendments (Without, biochar, compost and biochar + compost) and sub main treatments being different cobalt (Co) rates (0, 5, and 10 mg Co/L). Parameters measured at 80 days post-transplanting included plant height, dry weight, carotene content, nitrogen, phosphorus and potassium. At harvest, yield traits such as bulb diameter, total bulb yield, vitamin C and total sugar content were assessed. Soil nutrient levels, including available NPK, were also determined at harvest. The results indicate that both biochar and compost significantly improved onion growth and yield parameters compared to the control, as the superior treatment was the combined application of biochar and compost followed by compost alone then biochar alone. Also, the cobalt treatments had a positive effect, as this effect increased as the Co rate increased. Specifically, the highest rates of cobalt (10 mg/L) in conjunction with biochar and compost amendments resulted in the greatest increases in plant growth and nutrient content as well as bulb characteristics. Also, the soil available NPK increased due to soil additions, as the highest values were achieved with the combined treatment of boichar plus compost. These findings suggest that integrating biochar and compost amendments with cobalt spraying can effectively enhance onion growth and productivity under saline conditions.