The study on the effect of biological and chemical fertilizers and humic acid on the growth, physiological characteristics and essential oil content of catnip (Nepeta cataria L.)

In sustainable agriculture, biological fertilizers are an alternative to chemical fertilizers that they can improve the quality and quantity of medicinal plants. Biological fertilizers are consisting of useful bacteria and fungus that each one is produced for a special purpose, for example nitrogen fixation, releasing phosphate and potassium nutrients from their insoluble compounds. These bacteria are usually existed around the roots and help plant to uptake nutrients. In addition, they can be useful to the plants to uptake other nutrients, decrease diseases, improve soil structure and consequently stimulate more plant growth and increase quantitative and qualitative yield. This research was conducted to study the effects of biological and chemical fertilizers and humic acid on growth and physiological parameters of catnip (Nepeta cataria L.).
A factorial layout based on randomized complete block design (RCBD) with and three replications was conducted at experimental farm of Shahid Chamran University of Ahvaz. The first factor was included five fertilizer (included nitrogen-fixing biofertilizer (Azotobacter vinelandii), Phosphate solubilizing biofertilizer (Pseudomonas putida and Pantoea agglomerans), NF PS, chemical fertilizer), control and the second factor was two humic acid levels (such as 0 and 20 kg.ha-1). Growth parameters (such as plant height, leaf number and leaf area index, fresh and dry weights of aerial parts), photosynthetic pigments (chlorophyll a, b, total, carotenoid) and gas exchanges (net photosynthesis rate, quantum yield, transpiration rate, water use efficiency) were measured at beginning of flowering stage. The plants were harvested at full bloom stage and essential oil extraction was carried out with hydro-distillation method.
The results showed that application of biological and chemical fertilizers had significant effects on the measured traits of Catnip. The highest fresh and dry weights of aerial parts (203.33 and 37/44 g/plant, respectively) and plant height (44.08 cm) were belonged to combination of biological fertilizers. The lowest above traits were observed in control. Humic acid had not significant effect on the most measured traits except leaf area index and fresh weight of aerial parts. The amounts of photosynthetic pigments and gas exchanges were also affected by fertilizer treatments. The results showed that application of combination of NF and PS had significant effect on chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, net photosynthesis rate; water use efficiency and light use efficiency parameters of Catnip but had not significant difference with chemical fertilizer. The highest essential oil content was observed in PS treatment (1.30%) that it had not significant difference with chemical fertilizer (1.22%) and combination of biological fertilizers treatments (1.18%).
According to non-significant difference between chemical fertilizer and combination of biological fertilizers treatments in dry weight of aerial parts and essential oil content, an alternative combination of biological fertilizer NF and PS instead of chemical fertilizers is recommended.