Ultisols are by definition acid soils. In Hawaii they usually occur in the
zone. They are not found on the Big Island because as the name implies, Ultisols are
old or ultimate soils. Many thosuands of years from now some soils on the Big Island
now classified as Inceptisols may turn to Ultisols as nutrients are leached and clay
accumulates in the subsoil. As a group, the Ultisols are the least fertile of our soils.
But their value as agricultural soils is lowered more by their usual occurrence on
dissected landscapes on the windward sides of the older Islands. A combination of
steep slopes, high soil acidity, low fertility and heavy cloud cover renders our Ultisols
marginal for crop production.