A field experiment was conducted during the agricultural season 2016-2015 in the project of cultivating onion using the modern technologies of the Directorate of Basrah Agriculture in Khor al-Zubair - Basrah in order to study the effect of the mulching, concentration and the number of sprays with liquid sulfur zolfast in the growth and yield of the local red onion cultivar.         The experiment included three factors: the Interactions between three types of mulch (white, black as well as without mulch) and spraying with liquid sulfur Zolfast with three concentrations (0, 1.5 and 3 ml \ l) twice or three or four times. The experiment was implemented as Factorial Experiment Split Split Plot Design by Randomized Complete Block Design (R.C.B.D.) in three replicates and the arithmetic means of the treatments were compared using the least significant difference test (L.S.D at 0.05). The results showed that there is a significant increase in total chlorophyll, carbohydrate, nitrogen, potassium% and sulpher contents in the plants leaves mulched with black plastic as compared to non-mulched plants. Mulching with black or transparent white plastic show significant increase in phosphorus contents as well. Plants sprayed with zolfast at concentrations of 3 ml \ l and 1.5 ml \ l were superior in total chlorophyll content and percentage of nitrogen while those sprayed with concentration of 3 ml \ l contained high content of  carbohydrates, phosphorus, potassium and sulfur. The leaves of plants that were sprayed four times with zolfast significantly exceeded in their carbohydrate and potassium content, while those sprayed three times excelled in percentage of sulfur as such those were sprayed three or four times excelled in percentage of nitrogen & phosphorus. The interactions between the studied factors showed a significant effect on most of the traits.