Sowing date and nitrogen rate effects on growth, yield and yield components of two summer rapeseed cultivars
European Journal of Agronomy 19(3): 453-463
ISSN/ISBN: 1161-0301 DOI: 10.1016/s1161-0301(02)00136-3
Rapeseed (Brassica napus L.) has potential to become an alternate oilseed crop in eastern Anatolia, Turkey. Information on sowing date and nitrogen rate for rapeseed is not available in this region. Therefore, a study was initiated to investigate the effects of sowing date and nitrogen rate on the yield and agronomic characteristics of two genotypes of spring rapeseed (Tower and Lirawell) in Erzurum, eastern Anatolia, during 1994 and 1995. Four sowing dates were established at about 10-day intervals from mid April to lately May (19 April, 29 April, 9 May, and 18 May 1994; and 29 April, 9 May, 18 May, and 27 May 1995). Four N fertilizer rates established; 0, 80, 160, and 240 kg N ha-1. In both years, there were effects on plant growth, yield, and yield components due to sowing dates, nitrogen rates, and cultivars. Cultivars tended to respond similarly to sowing date and nitrogen rate for seed yield in both years of the study. In general, early sowings gave higher yields than late sowings in both years, except the first sowing (9 April) in 1994 growing season. From this study, it appears that seeding rapeseed from 29 April to 9 May gives a greater assurance for higher yields. The present results highlight the practical importance of adequate N fertilization in yield formation in summer oilseed rape and suggest that the rate of 160 kg N ha-1 will be about adequate for the crop to meet its N requirements. The yield differences measured for both sowing dates and nitrogen rates were primarily due to the changes in branch numbers, pod numbers per plant, and 1000 seed weights.