Organic manures enhance biomass and improve content, chemical compounds of essential oil and antioxidant capacity of medicinal plants: A review

The current farming systems strongly depend on chemical fertilizers (CF), which are widely applied to increase crop yield worldwide. However, although CF enhance crop yield in the short term, their excessive and long-term application can have adverse effects on environmental and human health. One of the most important goals of sustainable agriculture is substituting CF with organic manures. Organic manures can be used as a low-cost and safe alternative for CF. They contain essential nutrients for crop growth, improve soil conditions and nutrient availability, increase plant growth, and ultimately enhance yield. The application of organic manures to medicinal plants (MP) is more critical than to other plants, because organic manures not only enhance the growth and productivity of MP but also modify quality of their products. In this review, the effect of different types of organic manures on the biomass, content and chemical compositions of essential oil and antioxidant activity of various MP has been investigated. The included information was gathered from scientific databases such as Science Direct, Google Scholar, PubMed, and Scopus. Many of the collected studies showed that organic manures increase biomass and improve the quality of these plants. The findings of this review indicate that broiler litter (BL) and compost (C) are highly recommended as organic manures to promote biomass. Moreover, C, sheep manure, and vermicompost (VC) are suggested as the optimal organic manures for enhancing the essential oil content. Organic manures significantly changed the aroma profile of the essential oils and in many cases, they enhanced major chemical compositions. The usage of VC raised the content of the linalool of studied MP. Most of the organic manures, especially BL, VC, farmyard manure, and poultry manure increased the antioxidant activity of these plants. Hence, the utilization of organic manures can be recommended for productivity enhancement and quality improvement of MP.