The importance of exchangeable cations and resin-sink characteristics in the release of soil phosphorus |
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Authors: | D CURTIN J K SYERS G W SMILLIE |
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Institution: | Fertilizer and Lime Research Centre, Massey University, Palmerston North, New Zealand |
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Abstract: | The significance of exchangeable cations in the release of phosphorus by sequential extraction with water was evaluated in 11 acid (pH 5.0–6.3) New Zealand soils contrasting in P status and P retention. The release of P from Na-saturated soil exceeded that from the original Ca-dominated soils by up to four-fold. Possible explanations for the larger P release in the Na system include: (i) desorption of P induced by increased surface negative potential associated with the exchange of Na for Ca/Mg, and/or (ii) accelerated dissolution of Ca phosphate compounds or complexes resulting from the creation of a sink for Ca. The potential of a series of anion- and cation-exchange resin systems (AER and CER, respectively) as sinks for labile soil P was also examined. For all soils studied, P extracted by AER-HCO3 3 and that removed by sequential extraction with water. Also, the amounts of P extracted by AER-OH/CER-H and NaCl/ H2O were closely correlated ( r = 0.95**), suggesting similar release mechanisms. The results obtained indicate that charge-balancing cations, particularly Ca which is the predominant exchangeable cation in the majority of soils, exerts a more significant control on soil P equilibria in acid soils than is commonly recognized. |
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