Sequential phosphorus extraction using iron (hydr)oxide-impregnated filter paper strips

Phosphorus (P) is an important element for crop production. A low concentration limits crop growth whereas the residual quantity after fertilization contributes to eutrophication of surface waters. A key to success in the soil P management is its accurate estimation and potential supply to the plant. The objective of this project was to compare the soil P extractability between the Pi- filter strip method and P depletion without a sink (0.01 M CaCl2). The results were compared to those obtained using ammonium lactate (AL), Olsen (OL) soil P tests. The results showed that the efficiency of different methods decreased in the order Pi (62-85%) > OL (25-40%) > 0.01 M CaCl2 (8-24%) of the total P extracted by AL. A strong correlation (r = 0.99) was obtained between the pairs (Pi; AL), (Pi; OL), and (OL; AL). Further, it was found that all methods were equally well correlated (the r was between 0.88 and 0.90) with the depletion method. The soil with the highest P adsorption capacity had higher values of P extracted by the AL, Pi and OL methods but was lower in 0.01 M CaCl2 extractable P. The results indicated that in the soils studied, the efficiency of the Pi-filter strip method in comparison to the routine P tests (AL and OL) was not attributed to the soil properties. It was rather attributed to the length of soil P desorption time and the number of filter strips