This week’s column discusses the macronutrients known as secondary nutrients: Sulfur (S), Calcium (Ca), and Magnesium (Mg). Calcium and magnesium are found as cations, positively charged ions in the soil, while sulfur is typically found as sulfate, an anion, negatively charged.While are three are important, sulfur is especially critical to producers. Proteins are made up of amino acids and all plant proteins need sulfur containing amino acids.