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As growers receive results from their soil tests, I am commonly asked what is the difference between agricultural lime and gypsum. The follow up question is usually "can I use gypsum to raise my soil pH?" The answer is no.
Many soils in Alabama become more acidic over time. This is a natural part of how soils change over time. The processes of "liming" involves applying a material to neutralize that acidity. The most common product used is agricultural lime – calcium carbonate (CaCO3). Agricultural lime works by increasing the exchangeable calcium and neutralizing hydrogen ions.
Gypsum is calcium sulfate (CaSO4ˑ2H2O). Gypsum has a neutral effect on soil pH. This means that gypsum will not neutralize acid soils or effectively soil raise pH.
Both of these products, however, do provide a crucial plant nutrient, calcium. The amount of calcium in each material differs with its purity and type. Gypsum also contains sulfur, another needed plant nutrient.
So, if you your soil test indicates that you need to raise the pH of you soil, agricultural lime is what you need. The amount you need to apply depends on your soil test and the specific liming material you are interested in using (for example, calcitic lime, or dolomitic lime). If you do not need to apply any liming material BUT you do need to apply calcium, gypsum would be a potential choice for you to use. In the end, what you apply will revolve around cost as well as availability. In any case, if you are unsure of what to use or simply what to go over your options, call your local Extension office or a State specialist like me. We are here to help.
Extension Specialist, Commercial Horticulture
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