Evaluation of the electro‐ultrafiltration technique (EUF) to determine available P in neutral and calcareous soils

Abstract The electro‐ultrafiltration (EUF) method has been used to evaluate the K supplying power of North‐American soils but has not yet been used for P. 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 by three cuts of Ray‐grass (Lolium multifolium L.) growing over an 8‐wk period. Increasingly higher average concentrations of soil P were extracted by 0.01 M CaCl2 (0.24 mg kg−1), EUF at 50 V and 20°C (1.82 mg kg−1), water for 16 h (1.86 mg kg−1), EUF at 200 V and 20°C (12.0 mg kg−1), EUF at 400 V and 80°C (12.7 mg kg−1), Olsen (13.6 mg kg−1) and Mehlich 3 (33.5 mg kg−1). There was a very close relationship between the amount of P desorbed by EUF at 50 V and 20°C and 0.01 M CaCl2‐extractable P (r = 0.86**). Very significant relationships between the maximum P buffering capacity, as determined by batch equilibration, and the amounts of P desorbed in EUF‐fractions were observed (r = ‐0....