Response of Soybean to Applied Phosphate and Evaluation of Soil Test Methods of Phosphorus in Udic Ustochrepts

In low P soils (< 5 mg kg⁻¹ soil Olsen's P), significant increase in dry matter yield and total P uptake was observed up to 40 mg P₂P₅ kg⁻¹ soil, whereas in medium (5–9 mg kg⁻¹ soil Olsen's P) and high P (>9 mg kg⁻¹ soil Olsen's P) soils it was significant up to 20 mg P₂O₅ kg⁻¹ soil application. A significant and positive correlation was observed between soil phosphorus extracted by Olsen's and AB-DTPA methods. Olsen's and AB-DTPA extractable P and organic carbon content of these soils had significant positive relationship with dry matter yield and P uptake. The critical limit of available Pfor soybean was found to be 7.5 and 7.0 mg kg⁻¹ soil for Olsen's and AB-DTPA extractant, respectively.