Volcanic ash blankets almost two-thirds of the North Island (Baumgart 1954). Of the volcanic ash soils, rather more than one third are classified as yellow brown pumice soils (Baumgart 1954) derived from rhyolitic pumiceous ash having clay fractions made up principally of allophane (Fieldes and Taylor 1961). This mineral shows a considerable capacity for fixing phosphate (Jackman 1951). Yellow brown pumice soils present an interesting field of research for the soil scientist, since they are among the most dynamic
of soils- their equilibrium with the envirorunent is quite unstable (Baumgart 1954). An attempt is being made in New Zealand to bring the yellow brown pumice soils to a high level of production through both foresting and agriculture. Phosphate topdressing is essential for establishment and maintenance of improved pastures. It appears from the results of Jackman (1955) that a substantial proportion of fertilizer phosphate becomes converted to organic forms and accumulates as such. He has shown also that these soils in the virgin state contain a high proportion of their total phosphorus in the organic form. [From Introduction]
