Effects of nitrogen rates on yield, yield components, and other related attributes of different rapeseed (Brassica napus L.) varieties

Rapeseed is one of the most important oilseed crops in the world and, in Morocco, it may contribute to the improvement of food security in edible oils through developing performant cultivars and optimizing the crops management including nitrogen fertilization. The objective of this study was to evaluate the response of different Moroccan varieties to nitrogen application. Field trials were carried out at the experimental station of National School of Agriculture in Meknes, during two cropping seasons (2017–2018 and 2018–2019). Five varieties (“Narjisse”, “Moufida”, “Alia”, “Adila”, and “Lila”) were combined to different nitrogen rates (0, 30, 60, and 90 kg N ha−1). The experimental design adopted is a split split-plot with three replications, where nitrogen treatment was affected to main plot, variety to subplot, and year to sub-subplot. Results showed that dry matter, harvest index, oil content, seed yield per plant and yield components were significantly affected by nitrogen rates, with an upward trend in seed yield as the nitrogen rates increased. On average, seed yield increased by 50.33% for application of 90 kg N ha−1 compared to the control (without N fertilization). However, oil content declined from 41.08% to 37.81% with the increase of nitrogen level from 0 to 90 kg N ha−1. Additionally, for the other traits studied, the highest mean values were observed for 90 kg N ha−1, except harvest index which exhibited the greatest value for 60 kg N ha−1. Variation among the varieties was significantly large for all traits studied with a superiority of the variety “Alia” for seed yield per plant (9.82 g plant−1), number of pods per plant (151), and number of seeds per pod (24.05).