Use of ion-exchange membranes in routine soil testing
We developed and assessed a method for simultaneous ·extraction of plant available nitrogen, phosphorus, sulfur, and potassium using anion- and cation-exchange membranes (ACEM). The technique was found to be highly suitable for routine soil testing due to its simplicity, rapidness and accuracy. The study compared the amount of nutrients extracted by ACEM with conventional chemical-based extractants for P and K (0.5M NaHCO3) and N and S (0.001M CaCl) for 135 soil samples representing a wide range of soil types in western Canada. The nutrient availability predicted by ACEM was significantly correlated with the conventional methods. The correlation was not affected by the two different shaking times tested (one hour and 15 minutes), suggesting that extraction times as short as 15 minutes could be used in ACEM extraction. To evaluate the relative ability of ACEM and the conventional tests to predict actual nutrient availability to plants, canola plants were grown on soils in the growth chamber and actual plant uptake was compared to test-predicted nutrient availability. Phosphorus and potassium uptake by canola plants was more closely correlated with ACEM extractable P and K (r2= 0.84*** and 0.54***) than with 0.5M NaHCO3 P and K (r2= 0.70*** and 0.37***). Also, nitrogen and sulfur uptake by canola plants was significantly correlated with ACEM extractable-N and SO4 (r2 = 0.60*** and 0.70***) and with CaCl extractable-NO3 and SO4 (r2 = 0.57*** and 0.61 ***). Availability of all four macronutrients can be assessed in a single ACEM extraction. The higher correlation with plant uptake suggests that ACEM is a better index of macro-nutrient availability than conventional methods. The ACEM soil test could be readily adopted in routine soil analysis because of low cost and simplicity as well as its consistency over a wide range of soil types.
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