"施石膏肥料于" can be translated into English as "apply gypsum fertilizer to" or "administer gypsum fertilizer to" , depending on the specific context.
“Apply” is a commonly used verb in agriculture and horticulture to describe the act of putting a substance (such as fertilizer, pesticide, etc.) onto a surface or into the soil.
“Administer” can also be used, though it's more often associated with the act of giving or dispensing something (like medicine), but in some contexts, especially when referring to the controlled or intentional application of a substance, it can be appropriate.
In most agricultural contexts, “apply” would be the more natural and commonly used choice. For example: "Apply gypsum fertilizer to the soil to improve its structure."（将石膏肥料施于土壤，以改善其结构。）