Distribution of phosphorus in particulate, colloidal and molecular-sized fractions of soil solution

• Published in: Water research (Oxford) 2000-03, Vol.34 (4), p.1278-1284
• Main Authors: Shand, C.A, Smith, S, Edwards, A.C, Fraser, A.R
• Format: Article
• Language: English
• Subjects: colloids; Earth sciences; Earth, ocean, space; Exact sciences and technology; filtration; particles; peaty podzol; phosphorus; soil solution; Soils; Surficial geology
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/S0043-1354(99)00240-7

The total P in soil solution can be divided into three procedurally defined components namely molybdate reactive P (MRP), organic P (OP) and condensed P (CP). The amounts of these components in different size fractions of soil solution from a peaty podzol was determined using 1.6- and 1.2- μm filters to remove particles, and 0.45- and 0.22- μm filters to remove colloids. For MRP, 55% was associated with particles >1.2  μm and a further 23% with colloids >0.22  μm. For OP, 34% was associated with particles >1.2  μm and a further 46% with colloids >0.22  μm in size. CP behaved differently with no significant amount ( P≥0.05) associated with particles >1.2  μm, and around 54% associated with colloids >0.22  μm. In a separate experiment, the distribution of MRP, OP and CP in different molecular sized fractions of 0.45- μm filtered soil solution was determined using 100-, 10- and 1-kD ultrafilters in a stirred cell, part filtering the soil solution to minimize compositional changes in the retained fraction, and adding NaCl to minimize electrostatic exclusion. The 0.45- μm filtrate contained 116 of MRP, 212 of OP and 332  μg dm −3 of CP. Ultrafiltration showed 32% of the MRP, 95% of the OP and 90% of the CP was >10 kD. During ultrafiltration a gel, containing P mostly as OP, accumulated on the filter. The results highlight the quantitative importance of P associated with particulate, colloidal and high molecular weight materials in soil solution from an organic soil.