Fertilizer is a crafted liquid product used to restore Fertility in the Farm, Irrigated Farm, Greenhouse, and Greenhouse II. Along with the growing of Green Manure, it is the only method of restoring Fertility levels.
Fertilizer has to be supplied via a pipe, transport vehicles do not transport fertilizer. When different types of fertilizer is delivered to a growing plot, their properties will be mixed proportionally.
In the mid-game, Fertilizer I is generally produced using the the Ammonia byproduct from Sour Water stripping and Nitrogen from the Air Separator. It can be enhanced by adding Limestone and Sulfur to Fertilizer II. Alternatively, Fertilizer (Organic) can be sustainably produced through green methods using Compost.