Effect of humic acid and drought stress on some of physiological characteristics and agronomic traits of rapeseed (Brassica napus L.) cultivars

In order to investigate the effect of humic acid on some of physiological characteristics and agronomic traits of rapeseed (Brassica napus L.) cultivars under drought stress conditions, the present experiment was carried out as Split-split plot design randomized complete blocks design with 4 replications in Kaleybar city in 2019. The main plot, sub plot and Sub-sub plot included irrigation after 60, 90 and 120 mm water evaporation from class A evaporation pan, bean cultivars divided into 4 categories of Hayola 420, Sarigol, Traper and RJS003, and humic acid application on 5 levels (0, 100, 200, 300 and 400 mg.Lit), respectively. The results showed that the simple effects of drought stress, humic acid and cultivars traits measured at a probability level of 1%. The interaction between water stress and humic acid on chlorophyll content, plant height, number of pods per plant, grain yield and oil yield were significant. The effect of dual interaction (drought stress × humic acid and drought stress × cultivars) on chlorophyll index, plant height, number of pods per plant, grain yield and oil yield were significant. With increasing drought stress, the relative moisture content (20.54%), number of grains per pod (25.32%), 1000-grain weight (16.58%) and oil content (6.75%) decreased; While increasing the proline concentration (35.13%). The highest oil yield and grain yield were allocated to 60 mm of evaporation and 400 mg/l of humic acid and the lowest amount of oil and grain yield was assigned to 120 mm of evaporation and no use of humic acid. Humic acid increased the relative moisture content, number of seeds per pod, 1000-seed weight and oil percentage and decreased the amount of proline (26.31%). As a result, spraying 400 mg/l humic acid at different levels of drought stress improved physiological characteristics and increased production components compared to the control (no spraying). In the four cultivars evaluated, Hayola 420 cultivar had the highest grain yield and yield components. According to the results, humic acid reduces damages caused by drought stress.