Mike Hedley and Surrinder Saggar¹

Fertilizer and Lime Research Centre, Masssey University
¹Current address Landcare Research, Palmerston North

Mixed anion and cation exchange resin membranes have been shown to be more effective than several widely used soil tests at predicting pasture-growth responses to phosphate (P) fertilizers. These resin membranes have the potential to be used in a multi-element soil test including P, sulphur (S). potassium (K), calcium (Ca), magnesium (Mg) and some trace elements for which soil testing is considered appropriate. This paper reports a preliminary investigation of the relationships between the amounts of resin extractable major cations and amounts of exchangeable cations extracted with 1M ammonium acetate at pH 7.

Mixed resin membranes carrying between 0.20 anion and 0.25 cation meq charge extracted on average 41%, 60% and 58% of the exchangeable Ca. Mg and K from 1g samples of 15 New Zealand pasture topsoils. For each nutrient there was a very strong relationship between amounts of resin extractable cation and exchangeable cation.

In samples of leached and unleached Yellow-grey earth topsoils, which provided a wider range of exchangeable K values than found in the set of 15 soils, the relationship between amounts of resin extracted and exchangeable K was essentially similar to that to that of the set of 15 soils.

Mixed resin extraction provides a rapid method for assessing the available P, sulphate and exchangeable Ca, Mg and K status of New Zealand pasture soils. It's potential as a one-stop multi-element soil test should be evaluated on a wider range of soils and soil fertility situations.

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