| Summary: | A series of field trials were carried out during the following seasons 2000/01,2001/02 and 2002/03 to examine the growth and yield of two varieties of winter oilseed rape (Pronto a hybrid and Lutin a semi-dwarf hybrid). The response to agronomic management was examined in tenns of variation in nitrogen rate, nitrogen timing and seed rate. The semi-dwarf hybrid variety Lutin had a lower total biomass production and yield than the hybrid variety Pronto. In all trials Pronto produced on average 12.78 % higher yield than Lutin. The higher yield of Pronto was associated with a higher fertile pod number per m2 , seed number per pod and thousand seed weight but lower branch number per plant. Pronto had higher biomass production, leaf area index and green area index throughout the season when compared with Lutin. In three growing seasons, the response to nitrogen rate varied considerably with the highest yield achieved at 250 kg Nha-} in all experiments. Increasing nitrogen rate from 100 to 250 kg Nhao } increased yield of both varieties on average by 17.91 and 20.85 % for Pronto and Lutin respectively when averaged across all nitrogen rate experiments. Increasing nitrogen rate increased branch number per plant, fertile pod number per m2 , seed number per pod, and harvest index during each growing season. Although there was no significant effect of nitrogen timing on the growth and/or yield of oilseed rape, the highest yield was achieved in response to a 50150 split with the fust dressing in early March and the remainder at the start ofstem extension in April. Contrasting responses to seed rate were observed during the three seasons. Increasing seed rate up to 120 seeds m-2 increased yield of both Pronto and Lutin varieties in experiments during the 2000101 and 2001/02 seasons. The increased yield in response to seed rate was brought about by an increased number of fertile pods per m2 although branch number per plant decreased with increasing seed rate. Increasing seed rate in the 2000/01 and 2001/02 seasons resulted in higher yield and total biomass production but had no effect on harvest index. High seed rate (100 and 120 seeds m-2 ) increased LAl, GAl, radiation interception and biomass production. In the 2002/03 season, the yield, total biomass production and harvest index of both varieties increased when seed rate was increased from 80 to no seeds m-2 • During the 2002/03 season, increasing seed rate decreased branch number per plant, fertile pod number per plant and thousand seed weight but increased seed number per pod, seed number per m2 and harvest index of both Pronto and Lutin varieties.
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