Abstract
A field experiment was conducted on the Lyallpur soil series (Haplargids) to determine P requirement of canola
for obtaining 95 % relative yield. Phosphorus sorption isotherm was constructed by equilibrating 2.5 g soil with 0,
5, 10, 15, 20, 25, 30, 35, 40 and 50 mg P L-1
for 24 hours at 20°C using KH2P04 in 25 ml 0.01 M CaCI2 solution.
The data obtained was fitted to the modified Freundlich equation to compute P sorption parameters and derive
the equations to attain theoretical solution P levels of 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35 mg L-1with native
solution P level as control. The fertilizer doses were computed against these solution levels by using Freundlich
model and applied to canola crop. Maximum canola grain and oil yield of 2.94 and 1.17 Mg ha , respectively was
recorded at solution P level of 0.25 mg P L-1
which was obtained by adding P20S at 116 kg ha'. Maximum P
concentration in canola grain (0.61 %) was obtained at solution P level of 0.25 mg P L-\while in straw (0.14 %) it
was at 0.30 mg P L-1
• External solution P requirement was 0.215 mg P L-1
and internal P requirement found was
0.51 % for obtaining 95 % relative yield of canola
