The 'Compost Yard is a Tier 1 Resource building that also operates as a Service building, removing Waste from Shelters and other waste-generating buildings, converting it into Fertilizer for use on crop fields. Unlike most resource buildings, the Compost Yard has a recurring cost in gold to remain in operation.
Compost yards have three bins to generate fertilizer, a bin must be completely full before a multi-phase decomposition will occur. After completion, fertilizer can be applied to fields by clicking the Compost Yard building, clicking the bin in the informational pane that's ready, then clicking a button that will appear over fields to select one for application. After some time, the fertilizer will be worked into the field and that bin will be freed up to receive more waste for conversion.
Exact fertility change will vary depending on several factors (e.g. biome, initial fertility level, current fertility level) but application of fertilizer generally gives a fertility increase of 5-10%
Basic Strategy
Compost yards are negative-desirability buildings with a large radius and should be placed a reasonable distance from core residential districts despite their role in waste collection.
It is also beneficial to put Compost Yards somewhat near crop fields when possible, given the intended use of the final product.
When selecting a field for application, it is worth considering current fertility of available fields (which one will benefit most) and upcoming crop rotations (which fields will have large fertility drains in the near future).