Root depth depends on the crop type.
Grass has shallower roots than trees, which means grass likely needs to receive more frequent, shorter waterings. We automatically select a default value for each crop type, but you can adjust it if needed.
How do I select my root depth?
To measure your root depth, take several soil samples containing the roots using a soil probe and measure the roots. Increasing the root depth will increase the watering amount for a single watering.
Related article: How do I determine my crop type?