Mineral soils that have umbric or ochric epipedons, argillic horizons, and that hold water at <1. 5 MPa tension during at least 90 days when the soil is warm enough for plants to grow outdoors. Alfisols have a mean annual soil temperature of <8°C or a base saturation in the lower part of the argillic horizon of 35% or more when measured at pH 8. 2. (An order in the U. S. system of soil taxonomy. )