The Determination of Desorption Isotherms for Soil Phosphate Using Low Volumes of Solution and an Anion Exchange Resin

Abstract

Phosphate desorption isotherms were determined (a) by shaking I g soil with 3 ml O'OIM CaCl, solution plus different amounts of an anion exchange resin, and (b) by diluting soil with different volumes of O-OIM CaCl, solution. Adsorption isotherms were determined using a soil to solution ratio of I g to 3 ml. In soils of intermediate P status adsorption isotherms appeared continuous with desorption by method (a), but not with desorption by method (b), which predicted lower buffer powers than did (a). Method (a) led to increases and (b) to decreases in pH. Additions of dissolved silica had no influence on P desorption by method (b).

Diagnosis & Correction of Soil Nutrient Limitations in Intensively managed southern pine forests

“…Desorption isotherms are developed using sequential extraction with a dilute salt solution (Bhatti[6], Okajima [22], Brewster [9], Fox [15]), dilution (Bhatti[6], Brewster [9]), or exchange resins (Raven[24], Bache [1], Brewster [9]). Resorption, or the sorption of P following sorption and desorption steps, has rarely been investigated.…”

Determination of ‘labile’ phosphate in lake sediments using anion exchange resins: a critical evaluation

“…This parameter can vary with the volume of water present and the amount of exchanger used (Cooke and Hislop, 1963;Bache and Ireland, 1980). In one study (Brewster et al, 1975), the log of the water phase phosphate content (In Ps) was found to be linearly related to the total amount of P desorbed from the soil. In another investigation (Barrow and Shaw, 1977), the soluble P level (P 5 ) was found to be inversely proportional to the volume of solution and weight of exchanger used, and directly related to (Pr) 05 (where Pr was the amount taken up by the exchanger).…”

“…In another investigation (Barrow and Shaw, 1977), the soluble P level (P 5 ) was found to be inversely proportional to the volume of solution and weight of exchanger used, and directly related to (Pr) 05 (where Pr was the amount taken up by the exchanger). The amount of P desorbcd from soils can also be influenced by the amount of Ca 2 + in solution (Brewster et al, 1975;Barrow and Shaw, 1977).…”

“…It has been proposed (Brewster et al, 1975;Bache and Ireland, 1980) that most of the exchangeable P comes from dissolution of sparingly soluble calcium phosphates and displacement {by OH-) of phosphate bound by positively charged sites on hydroxylated forms of Fe and AI. For example:…”

“…It has been noted, however, that near quantitative retrieval of the P taken up by the exchanger requires multi-stage back-extraction procedures or resin destruction. For example, the exchanger phase was either washed repeatedly with small volumes of acidified NaCl (Barrow and Shaw, 1977;Bache and Ireland, 1980); or was boiled with small volumes of I M NazS04 (Brewster et al, 1975). Other approaches used include transfer of P-loaded resin into a small column before elution with IM NazS04 (Cooke and Hislop, 1963); and ashing the resin, followed by dissolution of the ash in HCI (Vaidyanathan and Talibadeen, 1970).…”