Fall is an ideal time to apply soil amendments that enhance soil chemistry and improve soil physical characteristics. Agricultural soils with ideal pH levels and good soil structure – with well-aggregated soil particles and plenty of pore spaces for air and water movement -- are important for crops to thrive.
Ag lime and gypsum are two common soil amendments that impact soil quality but sometimes there is confusion about their purposes and when to use one or the other amendment.
Ag lime is an acid-soluble material, often calcium carbonate or magnesium carbonate, applied to cropland to raise the pH of acidic soils. Acid soils, or soils with excess active hydrogen (H+), can curb a growing plant’s ability to reach its potential by limiting nutrient availability and biological activity. Scientists recommend soil pH of 6.2 to 6.8 as ideal for most crops.
Gypsum is calcium sulfate dihydrate. It is not acid soluble and is not recommended for altering soil pH. Gypsum is used to add sulfur and improve soil particle aggregation. The sulfate in gypsum binds with excess magnesium (an element which causes poor soil structure) in the soil to form Epsom salts that easily move down through the soil profile. The magnesium is then replaced by calcium to improve soil structure and produce better results for water holding capacity, root development and soil quality.*
“We use lime where we have very low calcium and low pH,” says Cory Schurman, national sales manager with GYSPOIL brand gypsum. “We use calcium sulfate (gypsum) where we have more neutral pH but where we have higher magnesium levels and lower calcium levels.”
Schurman adds that some growers use gypsum the year before they apply lime in order to lower magnesium levels and improve the efficiency of liming. “They work well together and tend to complement each other,” says Schurman.