Effect of Available P of Soils on Response of Ryegrass (Lolium perenne L.) to Applied Phosphate

A pot experiment on ryegrass with five phosphate levels was conducted to study the response of P on twenty soils differing in available P status. In low P soils (<5 mg kg⁻¹ soil Olsen's P) significant increase in dry matter yield was observed up to 60 mg P₂O₅ 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 40 and 20 mg P₂O₅ kg⁻¹ soil application, respectively. Total P uptake of ryegrass increased significantly in low and medium P soils up to 80 mg P₂O₅ kg⁻¹ soil application, while in high P soils it was significant up to 20 mg P₂O₅ kg_-1 soil. A significant and positive correlation was observed between soil phosphorus extracted by Olsen's and AB-DTPA methods. Olsen's extractable P and AB-DTPA extractable P showed significant positive relationship with control dry matter yield, relative yield, maximum yield, control total P uptake, relative P uptake and maximum P uptake. The critical limit of available P for ryegrass was found to be 8 and 7 mg kg⁻¹ soil for Olsen's and AB-DTPA extractant, respectively.