ارزیابی تاثیر زمان کاشت و آبیاری تکمیلی بر توزیع ماده خشک در ارقام کلزا (Brassica napus L.)

In the area with terminal heat and drought stress such as Gonbad, allocation of produced dry matter to reproductive organs is of great importance. In order to evaluate the effect of different temperature and moisture regimes on dry matter distribution and harvest index ofcanola an experiment wasconducted at Agricultural Research Station of Gonbad during 2005-2007. The experiment was a RCBD arranged in a split-plot in twoconditions, i.e. supplemental irrigation and rainfed. Five sowing dates (6 Nov., 6 Dec., 4 Jan., 5 Feb. and 5 Mar.) were selected as main plots and tow cultivars (Hyola401 and RGS003) werechosen as subplots. In both years of the experiment, at the beginning of seed filling period, the mean accumulated dry matter in reproductive organs, green leaves and stem at supplemental irrigation was more than that of rainfedconditions. There was not any difference for stem accumulated dry matter between the beginning of flowering and seed filling. The considerable differences between these two stages were a decrease in realative proportion of accumulated dry matter in green leaves and an increase in accumulated dry matter in reproductive organs. Supplemental irrigation did not significantly affect the mean harvest index, but it increased seed yield, due to an increase in aboveground dry matter. In all treatments, seed yield of Hyola401 hybrid was more than that of RGS003, due to higher harvest index. The relations of sowing date and supplemental irrigation with dry matter distribution, can be used incrop modeling.