Impact of application method and different levels of humic acid on vegetative growth parameters and yield components of canola (Brassica napus L.)

Application of organic materials, such as humic acid, prevent from environmental pollutionand also increases sustainability by decline the harmful impacts of industrial fertilizers in agroecosystems. Humic acid has quasi-hormonal activity and not only increases plant growth and absorption of nutrients, but also improves plant resistance to stress.
In order to determine the effect of application method and different levels of humic acid on vegetative growth parameters and yield components of rapeseed (variety Hayola 308), a factorial experiment was conducted in a completely randomized design with 10 treatments in 4 replications. Treatments included soil application of humic acid in 3 levels (1, 2 and 4 g/kg soil), spraying of humic acid in 3 levels (0.1, 0.2 and 0.4%) with irrigation water at 3 levels (1000, 2000 and 4000 mg/l) and control (acid humic-free). Soil application in the form of humic acid powder and in cropping time based on the soil weight of the pots and for spraying and consumption along with irrigation water, each of the spraying and together with irrigation water levels is divided into three equal parts and in three stages (establish of the plant, stem elongation and flowering) used. Spraying was performed at the end of the day and in order to make it more effective, several drops of moyan (foliar soap) were used to wet the leaves. The studied traits included leaf and stem fresh and dry weight, height bush, number of leaves and flowers, time to first flowering, silique length, seed per silique and silique per plant and 1000 grain weight, biological yield and harvest index.
The results of variance analysis of vegetative growth parameters, and yield components showed that all traits except leaf number per plant and leaf dry weight were significant at 1% level. The highest height, wet weight of leaf and stem and leaf and stem dry weight were related to treatment with 2000 mg/lit with irrigation water and the lowest was for control treatment. The highest number of flowers and amount of time to the first flowering was associated with 4000 mg/L treatment with irrigation water and control, whereas the lowest values for these traits respectively belonged to control and 4000 mg/L acid humic treatment with irrigation water. Also, the highest yield and yield components were related to treatment with 2000 mg/ L with irrigation water. The treatment of 2000 mg/L humic acid with irrigation water, due to the high dry weight of leaf and stem, seed per silique and silique per plant and 1000 grain weight, had the highest biological yield and harvest index, as well as the highest Biological yield and harvest index were 0.4% for spraying and 4 g/kg soil for soil application and its lowest for control treatment.
Application of humic acid can improve canola vegetative growth parameters and it could be used as a natural organic material to increase crop yield. The results showed that all three methods increased vegetative growth parameters, and yield components compared to control, but in general, 2000 mg/L acid humic with irrigation water was more effective than two methods of soil use and spray application.