Gypsum vs. mined calcium sulfate anhydrite for sodium management

August 30, 2009

In the August 31, 2009 Super Journal report, “Gypsum vs. mined calcium sulfate anhydrite for sodium management” (263 KB pdf document), a study was conducted evaluate the ability of two calcium sulfate based products – gypsum (calcium sulfate dihydrate) and mined anhydrite (calcium sulfate anhydrite) to reduce soil sodium levels when applied to Poa annua greens prior to leaching. Key conclusions were:

• Leaching of both treated and non-treated greens resulted in significant reductions in soil salinity, sulfur, chloride, magnesium, potassium, sodium, sodium percentage and nitrate.

• One application of either mined anhydrite or gypsum at 10 lbs product/1000 sq ft did not result in further reductions in soil salts or sodium, or in an increase in soil calcium or sulfur. It was simply leaching, whether on the treated or non-treated greens, that provided the only significant reductions in soil salts.

• The lack of observable effects caused by the application of either the mined anhydrite or gypsum has several possible causes. These include the possibility that:

• the products are not effective under these conditions due to low solubility or other issues

• the 10 lb product /1000 sq ft rate tested, which is the rate recommended on product labels, is too low to produce statistically significant changes when used in a single application

• leaching overwhelmed the effect of the product by moving all salts below the sampling area

• To follow up on the possibility that solubility was involved in the observed results, we obtained samples of commercial products based on gypsum (Allied Gypsum and Ultra Fine AG Gypsum Soil Conditioner), mined anhdydrite (Cal-CM Plus Mini-Prilled) and on an uncharacterized source of calcium sulfate (Cal-Sul) for analysis. Results of solubility tests clearly demonstrated that Cal-CM and Cal-Sul were much less soluble than the two gypsum products tested. While the low solubility of Cal-CM and Cal-Sul raises many questions about their potential as soil or water remediation tools, it is not the sole cause of the observed lack of efficacy in the field, since the highly soluble gypsum products also had no effect on soil salts or sodium.

• To follow up on the possibility that use rates were too low to produce detectable results, follow-up field tests will be conducted

• Until results from planned field tests confirm the optimal rate and use patterns for calcium sulfate-based soil amendments, the benefit of these applications for sodium management cannot be determined. For the time being, the best tool for reducing sodium and other damaging soil salts on turfgrass is leaching

Project title: Evaluation of gypsum and mined calcium anhydrite as pre-leaching soil amendments for sodium management on turfgrass

Principal investigators: Larry Stowell, Ph.D., CPAg and Wendy Gelernter, Ph.D., PACE Turf, LLC

Cooperator: Kevin Hutchins, Mission Viejo Country Club, Mission Viejo, CA

Report (263 KB pdf) posted 8/31/09