Gypsum (Solution-Grade)

Heavy Metals (PPM)

Arsenic       <10

Cadmium     <5

Mercury        <.2

Lead         16

Nickel         <5


Source:   Data From Oregon Department of             Ag Organic Certification Database

Gypsum is a staple in organic production if you believe in the power of calcium for plant health.

Solution-grade gypsum is used as a pre-plant calcium amendment or a mid-season calcium drench. Because of it's ability to "suspend" in water (it's not soluble and must be re-circulated in your mix tank), it is popular as a calcium feed mid-season.

Gypsum is the ideal source of soil applied plant-available calcium when your pH is above ~6.5. Gypsum is pH neutral, so it won't effect your soil pH in most circumstances. With a low pH, powdered lime or wollastonite can be used instead or in addition to gypsum.

Many high-calcium "calcareous" soils contain enormous amounts of calcium carbonate, which isn't plant available. Many crops in calcareous soils will test low in calcium! While applying gypsum sounds counter-intuitive, it floods the soil solution with a plant-avilable source of calcium for the plant. High magnesium soils (>20% base saturation) call also be improved with very large applications of gypsum.

Gypsum is often used to flocculate clay particles, improving the physical structure of soil. The benefit is greatest in soils where the Base Saturation of calcium is low.

Gypsum is also used to improve sodic soils (soils high in sodium). Sodic soils have poor water infiltration due to a lose in their physical structure. Gypsum helps flocculate the clay particles, opening up the soil structure for water to infiltrate. The leaching action of water can then flush excess sodium out of the root zone into deeper regions of the soil profile. As gypsum does not remove sodium by itself, the real key is large amounts of water applied slowly to flush the sodium out of the root zone.