Effects of Nitrogen Fertilizer Levels, Planting and Tillage Methods on Nitrogen Use Efficiency and Grain Yield of Rapeseed (Brassica napus L.) as Second Crop in Rotation After Rice

In order to investigate the effects of tillage, planting method and the levels of nitrogen fertilizer on the grain yield and nitrogen use efficiency in planting Rapeseed (Brassica napus L.), a split factorial experiment in complete randomized block design was conducted with three replications at Research Fields of Rice Research Institute of Iran in Rasht during two cropping seasons of 2016-2018. In the experiment, three tillage methods including the conventional tillage, minimum tillage and no tillage were considered as the main plots and two planting methods of direct planting and transplanting as well as the four amounts of nitrogen fertilizer of 0, 100, 200 and 300 kg ha-1 N from urea source as factorial in sub plots. The interaction between the tillage and nitrogen amount indicated that the treatment combination of minimum tillage at 200 kg ha-1 of nitrogen with the average of 4144.3 kg ha-1 had the highest grain yield. Treatment of 100 kg ha-1 of nitrogen had the highest nitrogen agronomic efficiency (17.68 kg ha-1), nitrogen use efficiency (32.40 kg ha-1), nitrogen apparent recovery (71.85 kg ha-1), nitrogen harvest index (75.48 percent) and nitrogen physiological efficiency (47.98 kg kg-1). Increasing the nitrogen consumption decreased all the traits related to the nitrogen efficiency and these traits were in their minimum values in the treatment of 300 kg ha-1 of nitrogen. The interaction between the tillage and nitrogen showed that the treatment of minimum tillage at 200 kg ha-1 of nitrogen with an average of 4144 kg ha-1 had the highest grain yield. In conclusion, the treatment of minimum tillage at 200 kg ha-1 of nitrogen due to the high seed and oil yields and treatment of minimum tillage at 100 kg ha-1 of nitrogen because of the high nitrogen consumption efficiency, energy saving and observance of the environmental issues are suitable for planting canola in paddy fields of Guilan province.