Which product releases sulfur in a form plants can absorb but requires oxidation before plant use?

Elemental sulfur is a unique product in nutrient management because it must undergo a biological oxidation process before it can release sulfate sulfur in a form that plants can absorb. This process involves the conversion of elemental sulfur (S) to sulfate (SO4^2-), which is the form of sulfur that plants can utilize. The oxidation typically occurs through the action of soil bacteria that facilitate this transformation.

In contrast, other options like ammonium sulfate and potassium sulfate already contain sulfur in a plant-available form, thus eliminating the need for oxidation. Gypsum, while it contains calcium and sulfate, does not require transformation for sulfur availability. Therefore, elemental sulfur stands out as the correct answer to the question regarding the need for oxidation prior to plant uptake.