The aim of our research was to determine the potential of waste generated during the production of chlorine for the synthesis of polyvinyl chloride as plant fertilizer in agriculture. For the production of fertilizer sludge produced when cleaning the saline solution, 78 vol % waste sulphuric acid from the dehydration of chlorine and calcinated magnesite were used. The product contains minimum: MgO – 16%, CaO – 9%, SO3 – 35%, and about 32% of water, mainly crystalline. The effect of the product on agrochemical properties of soil and crops was investigated in pot and field experiments. Soil fertilization with the product had a positive effect on the soil content of available magnesium and sulphate sulphur, their content in air-dry matter of plants and yields of spring rapeseed, and sugar beet roots.