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Assessment of Phosphorus, Nitrogen, Sulfur and Potassium Availability in Soil Using Anion and Cation Exchange Membranes

Huang, W. 1991. M.Sc. Thesis. Dept. Soil Science, University of Saskatchewan, Saskatoon, SK

Abstract

Anion and cation exchange membranes (ACEM) were evaluated as a routine soil test for phosphorus (P), nitrogen (N), sulphur (S) and potassium(K) for western Canada soils by comparing the membrane method with conventional tests in terms of i) relative amounts of ion extracted, ii) ability of the tests to predict plant uptake, and iii) operational simplicity. In a range of Saskatchewan soils, similar trends in predicted relative P availability were observed for anion exchange membrane (AEM), water extraction, bicarbonate extractable total P, and bicarbonate extractable inorganic P. Correlations between soil test values revealed AEM and water extractable P to be most closely correlated, consistent with the similar manner of P removal in the two extractions. Phosphorus availability as predicted by the tests was compared to actual P uptake by canola and wheat grown on 14 soils in a growth chamber experiment. P uptake by canola was highly correlated with the P extracted by AEM (r = 0.93 - 0.95), water (0.93 - 0.97), and bicarbonate extractable total (0.95) and inorganic (0.96) P. Uptake of P by wheat was not quite as highly correlated with amounts of P extracted by: AEM (r = 0.85 - 0.88), water (0.85 - 0.88), bicarbonate total (0.91), bicarbonate inorganic P (0.87). Anion and cation exchange membrane(ACEM) extractable N and S were compared to conventional CaCl2 extractable N and S. N and S removal from 8 Saskatchewan soils by the two methods were compared. Similar trends in predicted availability among the soils were observed for the ACEM and CaCl2 extractable N and S. Correlations between soil test values revealed ACEM and CaCl2 extractable N to be most closely correlated. Nitrogen and sulphur availability as predicted by the tests was compared to actual N and S uptake by canola grown on 8 soils in a growth chamber experiment. S uptake by canola was highly correlated with ACEM (r = 0.96) and CaCl2 extractable (0.96) S. Uptake of N by canola was not as highly correlated with test-predicted values: ACEM (r = 0.84) and CaCl2 extractable N (0.88). ACEM extractable K was compared to bicarbonate extractable K. In a range of 8 Saskatchewan soils, similar trends in predicted relative K availability were observed for the ACEM and bicarbonate extractable K. Potassium availability as predicted by the two tests was compared to actual K uptake by canola grown on the 8 soils in a growth chamber experiment. K uptake by canola was highly correlated with ACEM (r = 0.88) and bicarbonate extractable K (0.84). In this study, ACEM was similar to the conventional tests in predicting P, N, S and K availability to canola. The ACEM extractions, unlike the conventional chemical-based soil tests, are independent of soil type and may prove superior when a wider range of soils are being tested, especially for P and K. Simultaneous extraction of P, N, S and K using mixed AEM CEM is highly suitable for a routine soil test laboratory. ACEM was considered superior to the other methods due to low cost, simplicity, independence of soil type, and high correlation with plant uptake.