Studies on rapeseed winter cultivars, nitrogen rates and seeding depths in Northeastern Portugal

Abstract

Field experiments with rapeseed winter cultivars were carried out during the growing seasons of 2007/08 and 2008/09 in the Sta Apolónia farm in Bragança, NE Portugal. In the trial of 2007/08 four cultivars (Lucia, Recital, Nelson, NK Ready) and three N rates [basal+sidedress (0+50, 25+75 e 50+100 kg N ha^-1)] were included in an experimental design arranged as a split-plot. The cultivars were included as main-plots and the N rates as subplots. The trial of 2008/09 included four further cultivars (PR46W10, PR46W14, PR46W31 e PR45D01), of a total of eight, being the experimental set up arranged as a completely randomized design. A germination trial was conducted in a greenhouse with the eight cultivars and four selected seeding depths (1, 4, 8 and 12 cm). In the 2007/08 field experiment, the seed yield was not statistically different among cultivars. An average of approximately 3000 kg seed ha^-1 was achieved for each cultivar, as a result of a rainy and cool spring. In 2008/09 the seed yield was markedly lower in comparison with the previous year, as a consequence of the lack of rainfall in the months of March, April and May. On average, only one third (1000 kg seed ha^-1) of the production of 2007/08 was achieved. In the second year, significant differences among cultivars were observed. The production varied from 851 to 1558 kg seed ha^-1 in the cultivars PR46W14 and Nelson, respectively. No significant differences were found among N treatments. It seems that good rapeseed yields can be obtained with moderate N rates. The poor development of young plants in the autumn recommends an early seeding, preferably in September, in order to enhance the development of the young plants before the winter frost. In spite of the reduced seed size, the results showed the feasibility of seeding between 1 and 4 cm depth without significant reduction in the percentage of emergence.