Ferrous Sulfate Heptahydrate is an inorganic salt and a mining chemical. Ferrous Sulphate Heptahydrate is an Inorganic Compound. Ferrous sulfate is used as a soil amendment for lowering the pH of a high alkaline soil so plants can more readily access the soil's nutrients. In horticulture it is used for treating iron chlorosis, a yellowing of plant leaves caused by iron deficiency.