I have occasionally used scraps of drywall in my garden to increase drainage in heavier clay soils. What other benefit can gypsum offer to soil in a larger commercial level operation? Well in addition to the traditional benefits of improved drainage and reduction of surface crusting there are some lesser know benefits. (Must use soil test results to figure application rates based on CEC to improve drainage.) Did you know that in 1971 we were gaining 10#/Acre of atmospheric sulfur in rainfall annually? Now that we have reduced our atmospheric sulfur by “scrubbing” we no longer have that annual addition to our soils. Gypsum can be a good source of sulfur and also calcium.
What gypsum is not good for is correcting pH issues with your soil. Well let me correct that, some things that are side effects from low pH soil, gypsum will correct. For example high levels of aluminum (more common in low pH soils) create a toxic environment for plant root growth. Gypsum binds with aluminum reducing the soil toxicity. Adding 1Ton/Acre gypsum also reduces phosphorus run-off from our fields by reducing ponding and improving drainage. There are currently many thousands of acres in the United States under cost share management in concert with NRCS. There is also evidence of potential pathogen transport reduction with application of gypsum.
Safety considerations: Do not apply to snow covered ground. Pure sand and pure silt soils are not likely to show a response unless the soil surface tends to crusting. Apply within 5 days of manure applications to prevent run off. Long term use over recommended rates may cause calcium imbalances and pH increases. Prevent ruminants from grazing gypsum piles or applied fields until a rainfall or irrigation event of at least 1″. Do not exceed applications of 5 tons/Acre annually.