Gypsum – Composition and Uses
Q. What is gypsum? And what are its uses?
A. Gypsum, composed of calcium, sulphate, and water, has a chemical symbol of CA SO4 2H2O. It is an abundant natural mineral, which originated from the drying out of ancient seas and is quarried or mined in many parts of the world. Plants use almost as much calcium as phosphorus.
Until fairly recently, gypsum’s value as a fertilizer was not widely known or appreciated. Twenty five years ago, when Dr. Jacob Mittleider taught people to use it as a Pre-Plant fertilizer in high pH or alkaline soils, he was even sometimes ridiculed by fertilizer sellers, who asked if he had “gyped some folks today.”
Gypsum now enjoys an excellent reputation as a fertilizer. It is even used as a ‘clean green’ or organic soil conditioner and fertilizer. While other calcium sources raise soil pH, gypsum has a substantial advantage for use in high pH or alkaline soils, because of being pH neutral.
Gypsum is particularly useful in treating heavy or clay soils, where it is used to improve the soil’s
texture, drainage and aeration. It is also used to improve the structure of soil that has been compacted by heavy stock or machinery, in the improvement of sub-soils exposed by earth movement, and in reducing salinity of soils affected by dairy effluent or alkali.
In large-scale farming, gypsum is sometimes applied initially at 2 tons per acre (depending on soil type), and annual maintenance applications of 1 ton per acre are common.
For the home gardener, gypsum should be used by those with less than 20″ of annual rainfall at the rate of 2 pounds per crop – incorporated in the soil – in each 18″ X 30’ soil-bed or Grow-Box. For those with more than 20″ of annual rainfall, use agricultural or dolomite lime.