Evaluation of Available Phosphorus by Soil Test Methods in an Acidic Soil Incubated with Different Levels of Lime and Phosphorus

Abstract

An incubation study was conducted in laboratory to determine the effect of lime (L) as CaCO 3 and phosphorus (P) as TSP on soil pH and available soil P in an acid soil. Four rates of L equivalent to 0, 1, 2 and 3 ton CaCO 3 ha −1 and four rates of P equivalent to 0, 25, 50 and 75 mg P kg −1 were applied in combinations as treatments. The soil was incubated at field capacity for 8 weeks (wk) after which they were extracted using NaHCO 3 (Olsen), Mehlich-3, Kelowna and Bray & Kurtz-1 extrac-tants and soil pH was determined. Lime significantly (P < 0.001) increased soil pH. Phosphorus decreased it, though not significantly. Both L and P had significant effects (P < 0.001) on P availa-bility irrespective of extractants used. Two ton CaCO 3 plus 75 mg P kg −1 gave the highest available phosphorus. Mehlich-3 method extracted the largest amount of P (14.54 -67.35 mg • kg −1) while Olsen extracted the smallest amount (3.25 -32.77 mg • kg −1). The mean extractable P in soils was found to be in the order of Olsen < Kelowna < Bray & Kurtz-1 < Mehlich-3. Although the four me-thods extracted different amounts of P from soil, values of P extracted by the different methods were strongly correlated among themselves (R 2 = 0.87 to 0.95).