Effects of foliar application of humic acid extracts and indole acetic acid on important growth indices of canola (Brassica napus L.)

Vermicompost (VC) is a rich source of HA that improves plant growth and yield indices such as fresh and dry weights, plant height, stem diameter, leaf area, and chlorophyll index value. In this study, the effect of foliar application of HA extracted from different types of VC enriched with bacteria and/or fertilizers, commercial HA (CHA) and indole acetic acid (IAA) on the growth characteristics of canola (Brassica napus) in greenhouse conditions were compared. According to the results, the foliar application of HA extracted from VC had complete superiority over CHA and IAA in most traits except for the leaf number. Furthermore, the highest level of foliar application of HA (600 mg L−1) enriched with Azotobacter chroococcum (21Az) + Pseudomonas fluorescens (Ps 59) (HA-AS) generated the highest height, diameter, leaf area, and chlorophyll index value. Also, the highest stomatal conductance and photosynthesis rate were observed with the application of 600 mg L−1 HA extracted from VC enriched with nitrogen, sulfur, and phosphorus (HA-NSP) compared to the other treatments. Besides, dry and fresh weights and seed yield under HA-NSP and HA-AS treatments were at their highest rate. Among the extracted HAs, the one extracted from the nitrogen enriched VC had the lowest efficiency. Based on the present study, the HA extracted from VC enriched with Azotobacter, Pseudomonas and NSP is recommended to increase canola growth and production.