Game concept
County Fertility
From the game's encyclopedia
County Fertility exists in Counties located within the The Great Steppe, and can be grazed by Nomadic Rulers to increase their Herd.
A County's Fertility represents the quality of its pastures.
Fertility stabilizes around the Fertility Equilibrium, allowing Nomadic Rulers with a large Domain Limit to sustain their Herd growth. Fertility is affected by the Steppe Seasons and slowly replenished by Herders.
When a Realm's fertility is low, it is a sign to Migrate.
County Control slows down the rate at which Fertility grows by a percentage equal to the current control.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
County Fertility is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "County Fertility exists in Counties located within the The Great Steppe, and can be grazed by Nomadic Rulers to increase their Herd." It is part of The Great Steppe. It covers Fertility Equilibrium and Domain Fertility. Patch 1.20.1.2, from game/common/game_concepts/mpo_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/mpo_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.