Investigation of growth indices and yield of canola (Brassica napus L.) in competition with wild mustard (Sinapis arvensis L.) as influenced by different amount of nitrogen application

To evaluate the effect of different levels of nitrogen fertilizer on growth indices and competitive ability of canola (Brassica napus L.) against wild mustard (Sinapis arvensis L.), a split plot trial based on a randomized complete block design with three replications, was carried out at Agricultural Faculty of Bu-Ali Sina University, during 2008-2009. Experimental factors were amounts of nitrogen fertilizer of urea at four levels (100, 150, 200 and 250 kgN.ha-1) and five wild mustard plant densities (0, 4, 8, 16 and 32 plants.m-2). The results showed that wild mustard interference led to reduction of leaf area index (LAI), dry matter accumulation, crop growth rate (CGR), leaf area index duration (LAID), dry matter duration (BMD) and seed yield of canola, while these characteristics were increased with more nitrogen fertilizer application. The maximum indices were obtained at 250 kg N.ha-1 and weed-free condition, but generally, the least reduction in maximum LAI, CGR, LAID and BMD of canola affected by wild mustard competition occurred at 200 kg N.ha-1. In conclusion, the results showed that optimum level of fertilizer 200 kg N.ha-1, increased competitive ability of canola against wild mustard and improved yield and growth indices.