The Effects of Biological, Chemical Fertilizers and Humic Acid on some Microbial Parameters, Elements and Oil Quantity and Quality of Catnip (Nepeta cataria L.)

Catnip (Nepeta cataria L.) is one of the most important medicinal plants belonged to the Lamiaceae family that referred to considerable pharmacological, antimicrobial, antibacterial and pesticides activities of its essential oil in most of the literatures. The harmful effects of chemical fertilizers on the environment and human health and lack of soil organic matter in arid and semi-arid regions have resulted in an increase in the use of chemical fertilizers in these areas.Excessive use of these fertilizers has led to serious environmental pollutions during the last decades. With respect to the hazards of chemical fertilizers and the importance of medicinal plants, researchers have recently considered the application of biofertilizers and organic materials. According to literatures, the application of biofertilizers and organic fertilizers can be recommended as a proper alternation for the improvement of the quantity and quality of essential oil in Catnip.

This research was conducted as factorial layout based on a randomized complete block design (RCBD) with three replications at the research farm of the faculty of agriculture, Shahid Chamran University of Ahvaz, Iran. The first factor was included fertilizer treatments in five levels (Control (C), Azetobarvar-1 (Az), Phosphatbarvar-2 (Ph), Combination of Az and Ph (M), chemical fertilizer (Ch) included 150 kg.ha-1 granular urea (46% N) and 100 Kg.ha-1 triple superphosphate (46% p < sub>2O5)) and the second factor was comprised humic acid in two levels (0 and 20 Kg.ha-1). The studied traits in this research included soil microbial respiration and biomass carbon and soil organic matter contents, leaf nitrogen and phosphorus amounts, number and size of secretory trichomes, essential oil content, yield and composition. Leaf nitrogen and phosphorus concentrations were measured at the beginning of reproductive stage by Kjeldahl method and colorimetric method using a UV-2100-Unico spectrophotometer, respectively. Moreover, the soil microbial respiration and soil biomass carbon were determined by alkali absorption and the fumigated extraction, respectively, and soil organic matter was estimated by the modified Walkly and Blackʼs methods. Furthermore, the number and size of secretory trichomes was registered using Binocular microscope and essential oil was extracted by Clevenger-type apparatus and analyzed using GC and GC-MS at full bloom stage.

According to the results, the sole application of fertilizer treatment was positively affected on soil microbial respiration and biomass carbon, leaf nitrogen and phosphorus contents. The number and size of secretory trichomes, essential oil content and yield and essential oil composition were significantly influenced when fertilizer treatments and humic acid were applied simultaneously. The highest amount of soil microbial respiration as well as biomass carbon was detected in M and the lowest was observed in control. The application of Ch and humic acid was significantly improved the soil organic matter. However, no significant difference was found between these treatments and biofertilizers treatments. The lowest amount of soil organic matter was detected in control. The maximum content of leaf nitrogen element was observed in plant treated by Ch and minimum was registered in control. The highest level of leaf phosphorus element, the size of secretory trichomes and essential oil content were obtained when Ph was applied while there was no significant difference between this biofertilizer and Ch and M. The maximum number of secretory trichomes and essential oil yield was detected in plant treated with M. The most amounts of isomers 1 and 2 of nepetalactone and caryophyllene oxide was observed in Az, Ch and control, respectively, and least was in control, Ph and Ch, respectively. The highest level of trans- caryophyllene and (E,E)–Farnesene  was obtained in the oil of plant treated with M+ and Ch+ and lowest detected in Az+ and Ch-.

According to the results, to improve the quantity and quality of Catnip essential oil, the application of biological fertilizers instead of chemical fertilizers is recommended and further research is also required to investigate both the effects of applying humic acid alone and in combination with biofertilizers on some traits.