Agronomical strategy of plant density and nitrogen on winter rapeseed (Brassica napus L.) yield in interference with Lepyrpdiclis (Lepyrodiclis holosteoides Fenzl.) population

Rapeseed management for achieving maximum grain yield and quality is dependent on monitoring nutritional status of plant specially nitrogen accessibility during growth season, determining optimum density and controlling weeds. One important factor in crop management is the control of weeds in order to achieve high yield in canola. The absence of special herbicides for controlling weeds in this product has caused great damage to this product of rapeseedIn recent years, Lepyrodiclis (Lepyrodiclis holosteoides Fenzl.) has been privilege in rapeseed fields as an invasive weed. Despite rapid privilege of this invasive weed there is no research record on evaluating the competitive potential of Lepyrodiclis with rapessed in Iran. Current research was conducted to assessing competitive potential of Lepyrodiclis with rapessed under different nitrogen regimes and density levels.

A factorial experiment was laid out based on RCBD design with three replications in research field of higher education center of Imam Khomeyni in Karaj during 2015-2016 cropping year. Rapeseed was planted by hand and dried in a depth of 2 cm on September, Each plot consisted of six cultivars with a length of six meters and a line spacing of 30 cm. Simultaneously with the planting of rapeseed, the seeds of the mixed seedlings with soft sand were zigzagged on the sides of the rapeseed cultivating lines with respect to the desired densities. With the exception of weed Lepyrodiclis, weeds were continuously weaved with hands. Treatments were consist of nitrogen in form of urea (%46 nitrogen) in four levels 0, 50, 100 and 150 kg ha-1, rapeseed density in two levels 70 and 90 plants per m2 and Lepyrodiclis density in four levels zero, 5, 10 and 15 plants per m2.

Interactive effects of rapeseed density and nitrogen levels indicated that maximum pod per plant, grain per pod and grain yield were obtained when rapeseed density was 90 plants per m2 and 100 and 150 kg N ha-1 were applied. Interactive effects of rapeseed Lepyrodiclis and nitrogen levels revealed that the highest grain yield (3335 kg ha-1) was observed in 150 kg N ha-1 treatment in absence of Lepyrodiclis. Rapeseed grain yield showed 8, 14 and 28% reduction as Lepyrodiclis density increased to 5, 10 and 15 plants per m2 respectively.

It could be concluded that up to 100 kg per ha-1 nitrogen application and 90 plants per m2 rapeseed density not only can improve the grain yield and yield components of rapeseed but also can enhance the competitive ability of rapeseed against Lepyrodiclis.