Response of Lentil to P in Relation to Organic Carbon and Olsen-P in Soil

Field experiments were conducted at 18 different sites over 1986–91 with lentil (var. LL-56) on soils varying widely in organic carbon and Olsen-P contents with graded levels of P (0, 20, 40 and 60 kg P2O5 ha−1). Lentil crop responded significantly to applied P @ 40 kg P2O5 ha−1 in low and medium P soils whereas in high P soils response was significant up to 20 kg P2O5 ha−1 only. Magnitude of response declined sharply with rise in both organic carbon and Olsen-P contents in soil and with level of applied P. Superiority of organic carbon to Olsen-P as an index of P availability to lentil was observed. Predictability of response of lentil to P was found to increase by inclusion of organic carbon besides Olsen-P in the fertilizer response equation. A ready reckoner has been developed to identify P responsive soils.