Response of Sweet Basil (Ocimum bacilicum L.) to Different Nutritional Sources in Competition with Weeds

It is well accepted that application of chemical fertilizers contaminates the water and soil resources and reduces the quality of agricultural and medicinal products, which subsequently creates serious environmental issues. Currently, to improve soil fertility and have sustainable production, bio-fertilizers as an alternative to the chemical fertilizers have been widely applied. Product quality and production sustainability are very important parameters for medicinal products. In agricultural system, weeds are an inevitable part of the process which can negatively affect the production of the medicinal plant. Weeds can compete with medicinal plant for water, nutrient, light, space, and carbon dioxide access, which subsequently reduces quantitative and qualitative yields of the plant and increases crop yield losses. Therefore, this experiment was conducted to evaluate the effect of different fertilizer sources on biochemical traits of basil plant in control and non-control conditions with weeds.

This experiment was split plot based on randomized complete block design with three replicates and was conducted at Sari Agricultural Sciences and Natural Resources University, Iran. The treatments consisted of competition between plants and weeds (weedy and weed free) as the main factor and sub factors were fertilizer sources as: 1- control (no fertilizer), 2- NPK fertilizer (urea fertilizer (100 kg ha-1) + triple super triphosphate (100 kg ha-1) + potassium sulfate (80 kg ha-1)), 3- humic acid (15 l ha-1), 4- animal manure (20 ton ha-1), 5- NPK fertilizer (urea fertilizer (50 kg ha-1) + triple super triphosphate (50 kg ha-1) + potassium sulfate (40 kg ha-1)) + humic acid (7.5 l ha-1), 6- NPK fertilizer (urea fertilizer (50 kg ha-1) + triple super triphosphate (50 kg ha-1) + potassium sulfate (40 kg ha-1)) + animal manure (10 ton ha-1), 7- animal manure (10 ton ha-1) + humic acid (7.5 l ha-1) and 8- spraying macro and micro elements. The predominant weeds identified in the field included velvetleaf (Abutilon theophrasti), sorghum (Sorghum halepense), euphorbia (Euphorbia maculate) and wild melon (Cucumis melo. Var. Agrestis).

The results showed that the biochemical traits such as total phenol, total flavonoid and antioxidant activities had significant increment in weed infestation compared to weed free condition. Based on the results, the highest total fresh weight in the first harvest (11527 kg ha-1) and second harvest (15077 kg ha-1) belonged to chemical fertilizer + humic acid treatment. Animal manure + humic acid treatment had the highest (P < 0.05) total dry weight in the first harvest (1822.3 kg ha-1) and second harvest (2426.01 kg ha-1) compared to other treatments. According to the results, weed interference reduced (P < 0.05) the total fresh and dry weight of plant compared to weed control, where the total fresh and dry weight in the first harvest was decreased up to 50.31% and 42.29%, respectively and in the second harvest, up to 48.69% and 49.58%, respectively. Weeds density and biomass were affected by treatments, the highest weed density and biomass was observed by chemical treatments at the first and second stages of sampling, (49.33 and 36 plant.m-2, and 188.25 and 155.25 g.m-2, respectively).

Based on the results of current study, the integrated application of organic fertilizers had a positive effect on the production and biochemical traits in basil. Overall, the application of organic fertilizers reduces production costs and environmental pollution that can cause by the use of chemical fertilizers. Organic fertilizer also reduces weed dry weight which consequently decreases the damage caused by herbicides. Therefore, it can be suggested that organic fertilizers can be applied to produce healthy and sustainable products.