effect of sowing date and supplemental irrigation on grain yield and phosphorus distribution and remobilization in two canola (brassica napus l.) cultivars

to study the effect of sowing date and supplemental irrigation on grain yield and distribution and remobilization of phosphorus in canola (brassica napus), this experiment was carried out in 2 years (2005-07) in research station of gonbad. the study was carried out in two types of irrigation treatments (rainfed, supplemental). both experiments were carried out in randomized complete block design (rcbd) arranged in split-plot. the main plot factor was five sowing dates (6 nov., 6 dec., 4 jan., 5 feb., 5 mar.) and sub-plot factor was two cultivars (hyola401 and rgs003). late sowing date increased shoot p concentration. at the beginning of grain filling, p concentration of stem, leaf and pod ranged from 0.12 - 0.22%, 0.26 - 0.44%, and 0.49 - 0.80%, respectively. at maturity, p concentration of stem with pod-sheet, leaf and grain ranged from 0.04 - 0.10%, 0.16 - 0.24%, and 0.56 - 0.74%, respectively, across years and irrigation conditions. at maturity, mean grain p of hyola401 and rgs003 cultivars were 17.2 and 13.8 kg/ha in irrigated; and 13.5 and 11.0 kg/ha at rainfed condition. the existence of positive correlation between grain yield and shoot p remobilization rate shows the importance of shoots p in higher yield. the contribution of stem and leaf p remobilization on seed yield was strong and negative, explaining 90 and 85% of the variation for hyola401 and 93 and 91% of that for rgs003, respectively; indicating the increase of p remobilization contribution in seed yield under stress conditions. early sowing date could accelerate plant growth and phenological stages, hence, plant can escape from terminal heat stress. this led to increase in seed yield.