Inorganic Phosphorus Forms in Soufriere Hills Volcanic Ash and Volcanic Ash-Derived Soil

Soufriere Hills volcano is an active andesitic volcano located in the south-central part of Montserrat Island, West Indies. Phosphorus (P)-rich ash emitted from the Soufriere Hills volcano is expected to have effects on P retention and distribution in highly acidic soils surrounding the areas inundated with ash for several years. Phosphorus forms In ash varied with year of deposition with highest percent of P as Ca-P. Generally, the predominant forms of inorganic P in ash/soil mixtures and volcanic ash-derived soil were Ca-bound P > Al- or Fe-bound P > residual P > labile P > water-soluble P. Low soil pH in severely affected volcanic area soils suggests that Ca-P may exist in a partially dissolved form and will be the primary source of P for vegetation. Significantly high free Fe and A] oxides in these soils imply that bulk of P will remain as fixed P at the soil pH. High amounts of free Fe and Al oxides in soil may also play an important role in P adsorption and retention in these soils overtime. The cation exchange capacity and pH of surface material from severely affected areas suggest that surface material mainly consists of a high percentage of ash (primary mineral). Total inorganic P was relatively less in areas minimally affected by the volcano. Both water-soluble and labile P pools in the minimally affected areas were relatively higher than those in severely affected areas.