Combining green manure and cattle manure to improve biomass, essential oil, and thymol production in Thymus vulgaris L.

Abstract

Green manure can be used as an alternative to animal manure and organic compounds and can also be part of the management practices for medicinal plant production systems. The objective of this study was to use a combination of sunn hemp (Crotalaria juncea) and cattle manure in the fertilization of Thymus vulgaris L. plants to design better production strategies. The effects on vegetative growth, nutrient accumulation, essential oil production and chemical composition, photosynthetic pigments, and antioxidant activity were investigated. On the basis of four rates of cattle manure (0, 3, 6, and 9 kg m−2), additional four rates of green manure (0, 3, 6, and 9 kg m−2 sunn hemp) were added to each rate of cattle manure plus a positive control treatment (chemical fertilizer), totaling 17 treatments. The combination of organic manures (green and cattle manure) as well as the chemical fertilizer positively affected the dry weight of thyme leaves, stems, and roots. The combination of the highest doses of cattle and sunn hemp manure (9 kg·m−2 and 9 kg·m−2, respectively) resulted in an accumulation of total dry weight 10 times greater than that of the treatment without fertilization, which was significantly higher than that of the control treatment (0 kg m−2 cattle manure and 0 kg m−2 sunn hemp). Only application of green manure (Crotalaria juncea) has positive affected in dry weight. Significant increases in total and a and b chlorophylls and carotenoids were observed in thyme plants with the use of organic fertilizers. The essential oil production and chemical composition were improved by organic fertilization. The highest percentage of thymol (65.42%) was obtained in the group with 9 kg m−2 cattle manure and 3 kg·m−2 green manure. The application of both cattle manure and green manure increased the antioxidant activity of thyme, and this activity was correlated with high levels of carotenoids. The combined use of green and cattle manures is an inexpensive way to increase the yield of thyme and its essential oil and thymol production, and it can reduce the use of chemical fertilizers and thus is ecologically sound for the cultivation of medicinal plants.