However, if soils is alkaline because of high bicarbonate ions, or if irrigation waters contains bicarbonate, the soluble calcium in gypsum reacts with the bicarbonate to form insoluble calcium carbonate. The pH of the soil is decreased to the rage of 7.5 to 7.8 when bicarbonate is reduced. Gypsum is the best way to supply calcium to soil and roots below cultivation depth. Gypsum as metals protector Heavy metals, such as cadmium, copper, lead, and nickel, are toxic to plants in excess amounts, as well as to the people who eat the plants. Soils in or near some industrialized areas and soils very heavily amended with municipal sewage sludge might contain toxic amounts of heavy metals.
Plants generally absorb less of the heavy metals from soil when gypsum is applied.
Metals also become more toxic in highly acid soils. In those cases, use limestone to reduce acidity and metal toxicity. Some of the heavy metals plants absorb never more farther than the roots, the reason you should not grow root crops, such as carrots, in contaminated soil. Using Gypsum A calcium analysis of your garden's soil on a assay of calcium uptake in your plants is the best way to gauge your garden's gypsum needs. Most Cooperative Extension Service soil tests include calcium if you request it.