Ion‐Sink Phosphorus Extraction Methods Applied on 24 Soils from the Continental USA

Ion‐sink methods, such as resin membranes or FeO coated strips or filter papers, have been used as soil tests for plant available P. We have standardized a resin procedure and compared extractable soil P with the FeO method for 24 soils from the continental USA. Bray‐1 extractable P ranged from 0.3 to 221 mg kg −1 and Olsen's extractable P ranged from 1.4 to 131 mg kg −1 across all soils. We used anion resin membrane strips (RS) and traditional loose resin (LR) to extract soil P. Total surface area of one RS was 17.3 cm 2 , compared with 47.5 cm 2 for one FeO‐coated filter paper. We used one, two, or three RS saturated with bicarbonate (RS bic ) or chloride (RS Cl ), along with 1.5 g of moist LR saturated with either bicarbonate (LR Bic ) or chloride (LR Cl ). Using LR Bic , the mean P was 64.3 mg kg −1 compared with 52.5 with one RS Bic , 55.2 with two RS Bic , and 63.9 with three RS Bic Using LR Cl , the mean P was 63.2 mg P kg −1 compared with 48.7 with one RS Cl , 54.8 with two RS Cl , and 57.3 with three RS Cl The mean FeO‐P was 36.4 mg kg −1 Resin (Cl) hardly influenced pH of the extracting solution, LR Bic and RS Bic influenced pH most, and FeO‐strips had an intermediate effect on solution pH. This study shows that RS with a total surface area of 51.8 cm 2 can be used to extract soil P in place of more time‐consuming LR methods.