Fertility

Fertility is a property of a ground Tile. It affects the rate at which plants on that tile grow and reproduce, and can be affected by a variety of Weather, the Ground, Flooring, and certain player actions.

*See also Plant Growth Speed*

## Weather

Weather may positively or negatively affect fertility (`FertilityAddP`). These are the possible weathers that have an effect on Fertility. Multiple weathers active at the same time stack their bonuses additively. For example, Heavy Rain during Spirit of Harvest will increase the Fertility of tiles by 130%.

### Average effect on fertility

         While the weather variations across game are random, we can determine an average effect depending on the difficulty settings of the player. In almost all cases the effect are positive for the player, notably thanks to the Spirit of Harvest weather which is very likely to happen.

The following graphs and numbers are simulations of the weather effect on the fertility of Wheat made over 3 in-game years , assuming the sect achieves 500 Reputation around day 25. The assumptions made are :

* The fields are in acceptable Temperature ranges at all time (in a room-controlled temperature)
* The fields have a light source of 110 strength nearby (a Lamp Post) as shown in the example image
* The player does not have the Fiery Chasm or Frozen Furnace Natural Wonder, nor, if they have those, activate the Yin Yang Stela or Rainsword.
* 100 tile Qi. This assumption does not hold in practice except in early game, so average values for 500 Tile Qi are also provided.
* For the immortal case, no weather constraint is applied.

The averages fertility effects are :

* Normal difficulty : 13.7% bonus fertility on 100 tile Qi, 13.4% on 500 Tile Qi.
* Immortal difficulty : 14.4% bonus fertility on 100 tile Qi, 13.8% on 500 Tile Qi. The higher number is explained by the higher frequency of events.

### Weather fertility optimization

    The most important factor for the weather effect on fertility are the number of occurrences and durations of Spirit of Harvest and Polar night, as shown in the scatter plot. In case fertility is a concern for a player, they could thus optimize fertility values by :

* dispelling natural Polar Night weathers as they occur (this can only be done with Air of Cultivation is thus not very practical),
* dispelling any remaining "Spring is Coming" weather event at the start of Summer - since they are the only other weather of type 6 and can conflict with Spirit of Harvest (again, only through Air of Cultivation),
* in case neither Spirit of harvest nor any weather of type 1 is currently active towards the end of summer, force Rain events or Clear Skies to be active through Miracles or Fushu and Fei (doable early).
* dispelling Spirit of Harvest with low remaining duration towards the end of summer and apply miracles as explained above (needs Air of Cultivation)

To explain the last two recommendations, the average duration of Spirit of Harvest is 17 days, with a minimum of 14 days, and Spirit of Harvest is triggered by Common events, who happen every 2.60 days in Immortal difficulty. Moreover, Spirit of Harvest will have 100% chance of triggering if a weather of type 1 is active, and 57.1% chance otherwise. Since Common events can only trigger weathers of type 1 or Spirit of Harvest in summer, you would have a very good chance of triggering Spirit of Harvest by keeping a type 1 active through miracles towards the end of summer, possibly dispelling a current Spirit of Harvest effect up to about 8 days before the end of summer.

## Flooring

Flooring can reversibly reduce the Fertility of the tile on which it is built. Flooring reduces the base fertility to zero.

## Spirit Roots

A nearby Spirit Root significantly affects the Fertility with a Circular Range of 6 in the area around itself excluding its own tile. Blessed Spirit Roots increase Fertility by 1 (0% Bless) to 2 (100% Bless), while Cursed Spirit Roots decrease Fertility by 1 (0% Curse) to 3 (100% Curse). Spirit Roots that are produced by Plant reproduction are considered to have 0% Bless.

Both of these bonuses stack multiplicatively with weather bonuses.

## Ancient Formation

The Ancient Formation Wood Spirit Formation can increase **Fertility** by 2 (flat value) with Range 8 of its aura. This bonus stacks additively after the soil and weather bonuses.

## Corpses / Feces

A corpse of any Character, when allowed to decay on a tile or when buried in a Grave or Tomb, results in a boost to the Fertility of the area by 0.2 in a square radius of 2 tiles (a 5x5 square). This is unaffected by the Cultivation Level of the corpse, and does not happen for Vessel or Zombie corpses.

Similarly, Rubbish, Feces, or Dragon Feces can also increase the Fertility of the tile on which it decayed by 0.2.

This boost does not take place if the map tile is unexplored at the time the corpse or feces decays. It stacks multiplicatively with weather bonuses.

The maximum increase in fertility due to corpses or feces is capped to a maximum of 0.5 points. Once the fertility has been increased, it is permanent and does not decrease back to its original value.

This fertility increase also persists across soil type changes. For example, fertilizing a tile containing Soil (Fertility 1) 3 times increases its Fertility to 1.5. When that tile is converted into Spirit Soil or Spirit Water, the Fertility will increase to 2.5.

## Effect on plants

The first and most important effect of fertility is on the growth speed of plants, with improved fertility of the tile increasing the growth rate of the plant. Some plants also have a fertility requirement of the soil they are on, failing which they will not grow.

Fertility can affect the zoning of Fields and Herb Gardens. If a tile has 0 Fertility, a Field or Herb Garden cannot be zoned onto that tile.

Fertility also affects the locations at which plants undergo reproduction. If the Fertility of the tile is zero, a plant will not root divide to that location. This is usually caused by flooring or a cursed spirit root.

## References

1. ↑ `Settings/Weather/Weather.xml & Settings/Weather/Weather_Special.xml`
2. ↑ `Settings\ThingDef\Plant\Plant_LingZhi.xml [Fertility]` & `XiaWorld.Thing.SetFertility(), AddEffectSource` is called with `auraData.Radius` and not `Radius - 1` like other Effect sources, hence the extra range.
3. ↑ `XiaWorld.PlantThing.GetEffectSourceValue`
4. ↑ Scripts\Skill\class\zhen\zhen\_xtmlj.lua
5. ↑ 5.0 5.1 `XiaWorld.Map.AddFertilityAddtion`
6. ↑ `XiaWorld.Npc.CorpseStep`
7. ↑ `XiaWorld.JobBuryHim._OnToilDo`
8. ↑ `XiaWorld.ItemThing.OnDeath`
9. ↑ `XiaWorld.PlantThing.DoReproduce`