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

In recent years, ion exchange membranes (IEM) have been used successfully t o determine the availability of soil nutrient elements for plants. In gener al, the procedures proposed are applied to the determination of a single io n, and in only a few of these studies, the selectivity of these IEM was con sidered. Therefore, this work was conducted (a) to find the most suitable e xtraction conditions for phosphate (H2PO4-), nitrate (NO3-), and sulfate (S O42-) in soils by IEM and their subsequent determination by ion chromatogra phy, (b) to test the effectiveness and selectivity of IEM, (c) to compare t he results obtained by IEM with the common procedure for determining the av ailability of the soil nutrient elements, and (d) to verify whether a relat ion exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Ca mbisols located in four forest plots under natural conditions and four plot s fertilized with 100 kg P ha(-1) as triple superphosphate. The efficacy of the IBM was high (85% for SO42-, and 92% for H2PO4- and NO3-). Statistical ly significant correlations were obtained between the H2O4- extracted by IE M and the H2PO4- obtained by the Bray P1 procedure (r(2)=0.936) and with th e H2PO4- extracted using Saunders and Williams (1955) procedure(r(2)=0.370) . The correlation obtained between the amount of NO3- extracted with IEM an d that obtained using 2M potassium chloride (KCl) was also highly significa nt (r(2)=0.828). The IEM extraction allowed to know in a single extraction process and a single subsequent measurement by ion chromatography the conce ntrations of soil available H2PO4-, NO3-, and SO42- ions, which are of grea t 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.