Evaluation of Agronomic Attributes of Canola Cultivars under Different Plant Densities and Application of Humic Acid

To investigate the effect of humic acid application on agronomic characteristics of canola (Brassica napus L.) genotypes in different plant densities, a factorial split-plot experiment was performed using a randomized complete block design with three replications in the Seed and Plant Improvement Institute, Karaj, Iran. Plant density at three levels of 40, 60 and 80 plants/m2 and humic acid at two levels of 0 (non-application) and application of 0.3% were considered the main plots and canola genotypes including RGS003, Zafar, Julius, Jerry, Zabol10 and Hyola4815 were the sub-plots. The interaction effect of plant density × humic acid × cultivar was statistically significant for seed yield, oil yield, number of seeds per pod, number of pods per plant, biological yield and harvest index. Moreover, the interaction effect of plant density × cultivar was significant for oil percentage, 1000 seed weight, chlorophyll a, chlorophyll b and total chlorophyll. Generally, increased competition at the highest plant density caused an adverse effect on the tested traits of the canola cultivars. The Jerry cultivar with 40 plants/m2 (lowest density) and application of humic acid had the highest numbers of seeds per pod and pods per plant (with an average of 24.6 and 200.7, respectively) and 1000 seed weight (with the average of 4.9 g). Moreover, in the lowest plant density (40 plants/m2) and application of humic acid, the Jerry cultivar had the highest amounts of seed and oil yields (with an average of 5412 and 2196 kg ha-1, respectively). Accordingly, the examined canola cultivars had a positive reaction to the application of humic acid in different plant densities in particular at 40 plants/m2. Jerry cultivar had the maximum seed and oil yield under humic acid application condition when sown at 40 plants/m2.