Effect of different levels of nitrogen and planting density on rapeseed (Brassica napus L.) and lepyrodiclis (Lepyrodiclis holosteoides Fenzl.) competition

To investigate the effect of different lepyrodiclis (Lepyrodiclis holosteoides Fenzl.) densities on grain yield reduction, as well as qualitative and nitrogen agronomic efficiency of rapeseed (Brassica napus L.), a factorial experiment was conducted in a randomized complete block design with three replications in Karaj, 2016-2017. Factors included nitrogen content from urea fertilizer source at four levels (0, 50, 100 and 150 kg N/h, rapeseed densities (70 and 90 plants/m2) and weed density at four levels (0, 5, 10 and 15 plants/m2). The results showed that maximum yield loss at 70 and 90 plant densities of rapeseed/m2 was 26.54 and 78.45%, respectively, with 150 and 100 kg nitrogen. The highest percentage of oil and oil yield were 77.40% and 1504 kg/ha, respectively that were obtained by 90 plants/m2of rapeseed and 150 kgN/ha and no weed. The highest N-agronomic efficiency (89.19 kg/kg) was obtained by 90 rapeseed plants/m2 and without weed presence. The highest N-partial factor productivity was 36.24 kg/kg that was observed in 90 plants/m2 rapeseed and 50 kgN/ha. The results of nitrogen interaction and lepyrodiclis density indicated that the highest N-partial factor productivity (87.23 kg/kg) was observed in the treatment of 50 kg N/ha and absence of weed.