Fertility equilibrium is the level at which soil fertility will naturally stabilize based on the current crop schedule. At equilibrium, fertility loss from crops matches the natural replenishment rate. If multiple crops are in rotation, this value is an approximation since each crop has a different equilibrium point. Fertilizer is not factored into this calculation.
Soil fertility directly affects crop yield—at 60% fertility, yield is only 60%. Most crops deplete fertility as they grow. Fertility naturally replenishes when below 100% or can be restored by growing fertility-boosting crops or using fertilizers. Growing the same crop consecutively increases fertility loss and should be avoided by using crop rotation.
The monthly rate at which soil fertility restores itself without fertilizers. The less fertile soil, the higher replenish rate. If fertility exceeds 100%, natural replenishment turns negative and fertility will slowly decrease.
The average monthly fertility required to maintain the target level for the current crop rotation. This extra fertility must be replenished with fertilizer.