Phosphorus Desorption Quantity‐Intensity Relationships in Soils

Abstract

Phosphorus desorption quantity‐intensity (Q/I) relationships reveal information about the P release properties of a soil. This research was carried out to evaluate the P desorption characteristics of a group of soils of diverse properties and to compare several empirical models to describe P desorption Q/I curves. Samples of five soils (Typic Calciustoll, Udic Pellustert, Vertic Albaqualf, and Aridic Calciustoll surface soils, and Psammentic Paleudult subsoil) were enriched with five P concentrations (0, 25, 50, 75, and 100 mg P kg−1) and incubated for 31 d. Subsamples of each treated soil sample were equilibrated with different amounts of HCO−3‐saturated anion‐exchange resin. After 72 h the amount of P sorbed on the resin (Q) as well as the solution P concentration (I) were determined. Results from each subsample gave a point on the Q/I curve. The P release capacity of the soils used in this study was relatively low. In untreated samples, the solution P concentration when no P was desorbed (Io), an intensity parameter, ranged between <0.01 and 0.19 mg P L−1, while the maximum desorbed soil P (Qmax), a quantity parameter, was in the range 4.7 to 21.1 mg P kg−1. The corresponding P buffering power index, the slope of the Q/I curve at Io, ranged between 56 and 1703 L kg−1. These Q/I parameters were not closely related to any evaluated soil property, with the possible exceptions of CaCO3 content in calcareous soils and clay content. The P buffering power of a soil apparently depended on the availability of P sorption sites and their degree of depletion, and was not always directly related to the ability of a soil to release P. The P release activity of a P‐enriched soil depended on the desorbability of the applied P as well as the native labile soil P. Plots of P buffering power against intensity for a given soil were not affected by P enrichment. The Q/I curves could be best described by a proposed desorption Q/I equation (Q = a I−0.1 + b ln(I + 1) + c) and the Barrow power function, but the proposed equation followed the theoretical expected trend. The proposed equation is therefore recommended to describe P desorption Q/I curves.

Association of soil-test phosphorus with phosphorus fractions and adsorption characteristics

“…When STP was regressed against adsorption and ancillary soil attributes (Table 4), R 2 values were generally lower than those for the fractions, although release into solution depends on desorbability of P as well as the level of labile P (Raven and Hossner 1993). All tests were associated positively with EPC for which a significant relationship with 0.01 M CaCl 2 P was reported previously (Reddy et al 1980).…”

A rainfall simulation study on the relationships between soil test P versus dissolved and potentially bioavailable particulate phosphorus forms in runoff

“…However, there are a limited number of sorption sites in a kilogram of sediment matter, and the concentrations of these P forms must level out at some higher P saturation level (that was not covered by our material; i.e., the relationship actually has a shape of a Langmuirtype curve). By comparing the paper of Raven and Hossner (1993) to that of Barrow and Shaw (1977), it seems that at least some soils require excessive P additions to show a saturation of surface sorption sites. The former authors reported linear increase in AER-extractable P upon relatively modest P additions of up to 100 mg P kg -1 .…”

Sorção de fósforo em função do teor inicial e de sistemas de manejo de solos

“…(Barrow et al, 1998), o que justifica a menor adsorção do fosfato adicionado posteriormente (Raven & Hossner, 1993), como observado neste trabalho.…”

“…Adições de fertilizantes fosfatados (maior P pre ) proporcionam maior cobertura dos sítios de sorção, saturando-os e diminuindo a variação da energia livre proporcionalmente ao recobrimento da superfície (Fox & Kamprath, 1970;Ryden et al, 1977;Barrow, 1978). Isso aumenta a dessortividade e diminui a relação sorvido/solução (Hartikainen, 1991;Raven & Hossner, 1993;Tolner & Füleky, 1995), o que pode causar erros de interpretação nas isotermas de adsorção.…”