Effect of sowing date and supplemental irrigation on dry matter accumulation, yield and harvest index of two canola (Brassica napus) cultivars

In a two-year study, above-ground dry matter accumulation in canola (Brassica napus), and its relation with harvest index and seed yield were evaluated under vast environmental conditions. The experiment was a randomized complete block design arranged in split plot, conducted at Agricultural Research Station of Gonbad. It was arranged in two conditions, i.e. supplemental irrigation and rainfed. Two cultivars of spring type canola (Hyola 401 and RGS003) as subplots were grown at five sowing dates as main plots. The sowing dates were 6 Nov., 6 Dec., 5 Jan., 4 Feb. and 6 Mar. In both years, the mean above-ground dry matter in supplemental irrigation was more than that of rainfed conditions. The amount of rainfall at flowering and seed filling periods in 2005-6 was less than that of in 2006-7. This resulted that the efficiency of supplemental irrigation to increase above-ground dry matter and seed yield in 2005-6 was considerably more than that of in 2006-7. The increase of air temperature at late sowing dates caused significantly decreases in above-ground dry matter, harvest index and seed yield. Delay in sowing date led to critical periods of flowering and seed filling coincided with terminal high temperature and drought, which resulted in decrease in the number of days to flowering and physiological maturity stages. The amount of accumulated above-ground dry matter (except seed) at physiological maturity stage in Hyola 401 and RGS003 cultivars was 6290 and 6140 kg/ha in 2005-6, and 5795 and 5804 kg/ha in 2006-7, respectively. So the seed yield superiority of Hyola 401, compare to RGS003, was mainly due to higher harvest index, and there was not any considerable difference between two cultivars, for accumulated above-ground dry matter except seed.