Evaluation of crop traits and some physiological characteristics in terms of application of humic acid and different plant densities in some cultivars of winter rapeseed (Brassica napus L.)

In order to investigate the effect of different plant densities on yield and yield components on rapeseed cultivars under different levels of humic acid, this factorial experiment as split plot was conducted based on a randomized complete blocks design with three replications at the research field of Seed and Plant Improvement Research Institute located in Karaj during two cropping years 2014-15 and 2015-16. Plant density and humic acid in the form of factorial were placed at main and sub plots, respectively. Densities including (40, 60, and 80 plants per meter square), humic acid (non-application or control and humic acid application) and canola cultivars (Ahmadi, Okapi, Karaj1, Opera, L72, Sw102). The results of the experiment showed that the effect of the interaction of plant density and cultivar were significant for all assessed traits, excluding plant height and seed oil percentage and the highest mean traits was obtained at the density of 40 plants per square meter and L72 line. The highest amount of seed oil yield and seed yield was obtained from the treatment of plant density of 40 plants per square meter and L72 line and whereas the lowest amount of seed oil yield and seed yield was also obtained in this cultivar from the treatment of density of 80 plants per square meter. The obtained results indicated that the traits number of pods per plant, number of seeds per pod and one-thousand seed weight and pod length and grain yield and total chlorophyll were significant with the application of humic acid treatment. In the present research, the application of humic acid through improved soil fertility and nitrogen availability increased yield and yield components, particularly, pod length. Comparison of the average of traits of leaf relative water content and total chlorophyll indicated the superiority of the density of 40 plants per square meter and the highest rank was obtained from this treatment.