Phosphate Forms in Particle Size Separates of Irish Soils in Relation to Drainage and Parent Materials

Abstract

AbstractParticle‐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.