Particle-size separates of sand, silt, and clay from 24 representative Irish soils were analyzed for total, inorganic, and organic P (Mehta & Legg), and for forms of inorganic P (Chang & Jackson). In general, all forms of P were highest in the clay fraction and lowest in the sand. The inorganic P of the clays and silts was mainly iron-P whereas calcium-P was the dominant form in the sand fraction.
The influence of parent material on the P content of the separates was examined, and it was found that soils of limestone origin had a higher content of calcium-P in their separates than did those from the shale-derived soils. The sands of the shale soils contained more total P than the same fraction in the limestone soils.
Drainage also affected the distribution of P. In general, the clays and silts from the well-drained soils were higher in total P, but total and organic P and the proportion of organic P to total P was higher in the sands of the poorly-drained soils than in the sands of the well-drained soils.
A significant negative correlation (−0.61) was obtained between the percent clay in the soil and the total P content of its clay fraction.