Soil pH describes the soil's acidity or alkalinity. Extremely high or low pH (on a scale from 0 to 14, and in which 7 is neutral) can have a negative effect on the health of plants and soil biota. In soils with pH below 5.5, acid-sensitive agricultural plants are adversely affected and the risk of subsoil acidification increases. Soil pH is an important indicator of chemical processes that occur in soil, affecting soil processes governing nutrient availability. Although soil acidification is a natural process, it can be accelerated under agriculture. Soil pH represents a signficant constraint to production in many areas of Australia, with the economic loss from soil acidification across Australia, estimated to be up to six times higher than from dryland salinity.