Phosphate Retention by New Zealand Soils and Its Relationship to Free Sesquioxides, Organic Matter, and Other Soil Properties

Abstract

Phosphate retention from KHzP04 solution at pH 4.6 was measured in some New Zealand soil profiles, arranged in sequences of increasing weathering and leaching, from sedimentary and volcanic parent materials. P retention from KHzP04 solution correlated closely with Pretention measured by adding solid Ca(H;;P01)'z.H20 to moist soil and subsequently measuring water-soluble P. P retention by topsoils correlated closely with organic carbon, total nitrogen, loss on ignition, organic phosphorus, Tamm Al and Fe, and neutral citrate-dithionite Fe. Subsoil P retention correlated closely with Tamm Al and Fe and citrate-dithionite Fe. Soil organic matter was not considered to be directly concerned in Pretention; the close correlation with P retention followed from a close correlation between soil organic matter and Tamm Al and Fe. On each parent material, Tamm AI, Fe, and P retention increased with degree of weathering to a maximum in moderately weathered soils of silt texture and then decreased in strongly weathered soils of clay texture. With increasing degree of leaching within the profile, P retention and Tamm Al and Fe decreased in topsoils and increased in subsoils. P retention per unit of Tamm Alar Fe was similar in topsoils and subsoils. Allophane in soils lowered the P retention per unit of Tamm Alar Fe. Soils with allophane contained appreciable Tamm Si (> 5 ruM Si ). Possibly the Tamm Si combined with Tamm AI and Fe, thereby preventing P retention by the AI and Fe. © 1965, Taylor & Francis Group, LLC. All rights reserved.