Impacts of fertilization systems on nitrogen loss and yield of oilseed rape (Brassica napus L.).

Farmyard manure is considered as a source of plant nutrient supply, but high N loss and low N use efficiency are often serious challenges facing this source of nutrient. It is supposed that a combination of manure with inorganic fertilizers can reduce this problem. A two year experiment was conducted in 2004-2005 at Mazandran province of Iran in order to study the effects of manure, inorganic nitrogen and combination of manure-inorganic nitrogen on N loss and yield of winter oilseed rape (Brassica napus L.) under rainfed conditions. Treatments included 0, 50, 100 and 150 kg N ha(-1) urea (F0, F50, F100, F150), 100 kg N ha(-1) urea + 50 kg N ha(-1) manure (F100M50), 50 kg N ha(-1) urea + 100 kg N ha(-1) manure (F50M100), 150 kg N ha(-1) manure (M150). The highest grain yield (3 ton ha(-1)) was obtained with the 150 kg N ha(-1) as urea treatment in both years. Grain yield in M150 treatment was significantly lower (p < 0.05) than F150. However F100M50 and F50M100 resulted in similar yields compared with F150 treatment. Results also showed that F100M50 and F50M100 treatments decreased N loss (4 and 3 kg N ha(-1) year(-1), respectively) compared to application of manure alone (33.5 kg N ha(-1) year(-1)) and F150 (36 kg N ha(-1) year(-1)). Overall, it could be conducted that F100M50 is the best treatment because it produced similar grain yield compared to F150 while resulted in lower N loss as well.