The effect of plant growth stimulants on yield and yield components of canola (Brassica napus L.) under drought stress

The purpose of this research was to determine the effects of biostimulats application on the yield and yield components of canola (Brassica napus L.) in a semi-arid region based on Amberje classification in Ilam province. The experiment was carried out as split plots arrangement based on randomized complete block design with three replications. The main plots were two irrigation regimes after evaporation of 80 and 140 mm from class-A evaporation pan and soil moisture compensation to the extent of field capacity in silty clay loam soil texture. The sub-plots were as 1- control (application of chemical fertilizers according to soil test), 2- compound 1 and L-amino acid (glycine, betaine and proline) spraying, 3- compound 1 and fertigation of 5 kg per hectare of humic acid in two stages (after the second irrigation and the beginning of shoot elongation) 4-compound 1 and spraying fulvic acid 5-compound 1 and spraying seaweed extract, 6-compound 1 and the co-application of treatments 2, 3 and 5. In all treatments, foliar spraying was done with a concentration of 5 per thousand at the late rosette stage and the beginning of flowering. Quantitative traits measured were seed yield, number of seeds per pod, number of pods per square meter, thousand grain weight and concentration of nutrient elements. Statistical analysis of data was done with SAS software and mean comparison was done with Duncan's test. The results showed that drought stress caused a significant decrease in yield and yield components, but the combined application of growth stimulants caused a significant increase in grain yield compared to the control. The amount of increase of grain yield without drought stress and under drought stress were 16.2% and 21.1%, respectively. These data indicated the greater effect of growth stimulants on increasing grain yield under drought stress than without drought stress. In normal condition, the application of amino acid significantly increased the grain yield by 14.4% compared to the control. In the condition of drought stress, the best results were obtained by combined application of growth stimulants. The application of growth stimulants improved the absorption of nutrient elements under drought stress. So, in the case of potassium, which is an important element in improving plant growth under drought stress, the application of fulvic acid had a significant effect on the increase of potassium concentration compared to the control, and its concentration increased from 2.9% to 3.8%. Also, the combined application of growth stimulants increased potassium concentration up to 3.6%. The results of this research showed the increase of drought tolerance and the improvement of canola growth with the combined application of growth stimulants.