Evaluation of Morphological Traits, Yield, and Essential Oil Changes of Basil (Ocimum basilicum L.) under Influence of Organic Fertilizers

Medicinal plants are rich resources for traditional medicines and in this regard play an essential role in the development of human culture. Basil (Ocimum basilicum L.) belongs to the Laminaceae family and can be found in tropical Asia, Africa, Central America, and South America. Basil is traditionally used worldwide as a medicinal herb to treat numerous ailments. The leaves and flowering tissues are traditionally used as antispasmodic, carminative, digestive remedies, to treat abdominal cramps, fever, poor digestion, migraines, insomnia, depression, dysentery, etc. Application of chemical fertilizers in order to eliminate residues of this chemichal substances from crop to ensure consumer health and environmental protection is one of the major challenges in sustainable production of medicinal crops. The application of organic fertilizers such as farmyard, vermicompose, and humic substances as an alternative to chemichal fertilizers to improve soil fertility in sustainable agriculture is currently being discussed. Application of organic fertilizers in addition to modifying soil physical and chemical properties, provides nutrients for the plant in long-term. Various studies have also shown the positive effect of organic fertilizers on increasing the quantitative and qualitative yield of medicinal crops. Therefore, the present study was conducted to investigate the effect of cow manure, vermicompost, and humic acid on some morphological traits, dry matter yield, and production of basil essential oil.

The experiment was conducted as a factorial based on a randomized complete block design with three replications at a farm in Oshnavieh city in the West Azerbaijan Province in 2014. The treatments included organic fertilizers (20 tons ha-1 farmyard, 7.5 and 15 tons ha-1 vermicompost, and control) and humic acid application (soil application, foliar application and not application as control). The measured traits included plant height, lateral stems number, lateral stems length, flowering stems number, leaf number per plant, leaf chlorophyll index, dry matter yield and essential oil percentage. Data analysis was done using MSTAT-C statistical software and means were compared using LSD test at 1% or 5 % probability levels based on the significance level in each trait.

The results showed that application of organic fertilizers significantly increased plant height, lateral stems number, lateral stem length, flowering stem number, and leaf number. The highest essential oil yield (2.94 g m-2) was obtained using 15 tons ha-1 vermicompost. Both foliar and soil application of humic acid treatments had the highest lateral stems number (13.1 per plant) and essential oil yield (2.75 g m-2) and humic acid foliar treatment had the highest flowering stem number (22.9) and essential oil percentage (0.59%). All treatments of organic fertilizer and humic acid increased leaf chlorophyll index compared to control. Application of 15 tons ha-1 vermicompost combined with or without humic acid produced the highest dry matter yield (with an average of 538.6 g m-2) that showed 99.6% increase compared to control (not application of organic fertilizers and humic acid). It seems that the application of humic acid and organic fertilizers increased the absorption and transport of nutrients such as nitrogen, phosphorus, potassium, calcium and magnesium as well as water absorption by the plant and by this way, the morphological and growth traits of plant increased. On the other hand, application of organic fertilizers not only increased the available nutrients to the plant, but also improved soil physical conditions and biological processes and provided a suitable environment for root growth. Consequently, organic fertilizers increased dry matter production and essential oil content and yield.

The findings of this study showed that organic fertilizers and humic acid application had significant effects on morphological traits, yield, and essential oil content of basil. So that, these treatments significantly increased the value of morphological traits. The highest dry matter yield was obtained by application of 15 tons ha-1 vermicompost combined with or without humic acid. The treatment of foliar application of humic acid had the highest essential oil content. The highest essential oil yield was obtained by the application of 15 tons ha-1 vermicompost. Finally, the application of organic fertilizers could be used in sustainable agriculture to improve of quantitative and qualitative yield of basil and reduce the application of chemical fertilizers.