Extraction of soil‐available phosphate, nitrate, and sulphate ions using ion exchange membranes and determination by ion exchange chromatography

Abstract

In recent years, ion exchange membranes (IEM) have been used successfully to determine the availability of soil nutrient elements for plants. In general, the procedures proposed are applied to the determination of a single ion, and in only a few of these studies, the selectivity of these IEM was considered. Therefore, this work was conducted (a) to find the most suitable extraction conditions for phosphate (H₂PO₄ ^‐), nitrate (NO₃ ^‐), and sulfate (SO₄ ^2‐) in soils by IEM and their subsequent determination by ion chromatography, (b) to test the effectiveness and selectivity of IEM, (c) to compare the results obtained by IEM with the common procedure for determining the availability of the soil nutrient elements, and (d) to verify whether a relation exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Cambisols located in four forest plots under natural conditions and four plots fertilized with 100 kg P ha^‐1 as triple superphosphate. The efficacy of the IEM was high (85% for SO₄ ^2‐, and 92% for H₂PO₄ ^‐ and NO₃ ^‐). Statistically significant correlations were obtained between the H₂PO₄ ^‐ extracted by IEM and the H₂PO₄ ^‐ obtained by the Bray P1 procedure (r²=0.936) and with the H₂PO₄ ^‐ extracted using Saunders and Williams (1955) procedure (r²=0.370). The correlation obtained between the amount of NO₃ ^‐ extracted with IEM and that obtained using 2M potassium chloride (KCl) was also highly significant (r²=0.828). The IEM extraction allowed to know in a single extraction process and a single subsequent measurement by ion chromatography the concentrations of soil available H₂PO₄ ^‐, NO₃ ^‐, and SO₄ ^2‐ ions, which are of great plant nutrition interest. Phosphorus extractable with IEM yielded a close relationship with biomass production and could be used for determining the P requirement of these forest trees.

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