Evaluating plant-available phosphorus with the electro-ultrafiltration technique
Simard, R.R. | Tran, T.S.
The electro-ultrafiltration (EUF) technique successfully evaluated the short-term and long-term supplying power for many essential plant nutrients of European and Asian soils but has not been evaluated for P in North America. The objective of this study was to compare the capacity of EUF with other extraction techniques to predict the plant availability of soil P and P fertilizer responsiveness of oat (Avena sativa L.) and corn (Zea mays L.) grown in the greenhouse. Increasingly higher average concentrations of soil P were extracted by EUF at 50 V and 20 degrees C (1.53 mg kg-1), water (2.28 mg kg-1), EUF at 200 V and 20 degrees C (4.76 mg kg-1), 0.5 M NaHCO3 (13.0 mg kg-1), HCO3(-) resin (41 mg kg-1), EUF at 400 V and 80 degrees C (44.2 mg kg-1), and Sr citrate (51 mg kg-1). The P desorbed by EUF at 20 degrees C was smaller than the 0.5 M NaHCO3 P in acidic soils while comparable amounts were desorbed by the two methods from neutral to calcareous soils. The total amount of P desorbed by EUF between 30 and 55 min at 400 V and 80 C was equivalent to chemical methods but less precise than HCO3(-) resin in predicting the amount of P uptake by oat and corn as well as the fertilizer responsiveness of oat grown to Zadoks 71 stage. The prediction of P availability by the different EUF fractions could not be improved by the inclusion of selected additional physical and chemical characteristics of the soils studied. The desorption of soil P by EUF provides an evaluation comparable to chemical methods of the P-supplying power of northeastern North American soils. The large amount of time involved in the EUF extraction limits its applicability as a soil-testing procedure.
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