The effect of different organic amendments on growth, secondary metabolites and antioxidant properties of Artemisia afra

Abstract

Traditional medicine plays a crucial role in treating various ailments and is frequently used as a primary or supplementary therapy. The increased demand for commonly used medicinal plants, such as Artemisia afra, has put pressure on wild populations and threatens their survival. During the first COVID-19 outbreak, there was a surge in demand for A. afra as a remedy, leading to increased prices and maximum harvesting rates. To address the risk of over-exploitation, this study investigated the effects of different organic amendments on the growth, secondary metabolites, and antioxidant properties of A. afra, aiming to establish a sustainable and feasible cultivation approach. Four organic amendments were selected in response to the increasing demand for organically cultivated medicinal plants. These included vermicompost, mushroom compost, poultry and kraal manure, mixed with coarse river sand at a ratio of 70% sand and 30% organic amendments. The results highlighted a significant improvement in growth parameters with the use of poultry manure, likely due to its rich nutrient content compared to other organic amendments studied. Poultry manure also exhibited the highest concentration of secondary metabolites (polyphenols and flavonols) and antioxidant activities in A. afra, including (ferric reducing antioxidant power (FRAP), 1,1-diphenyl-2-picrylhydrazyl (DPPH) and Trolox equivalent antioxidant capacity (TEAC). Furthermore, there was a strong correlation between secondary metabolites and antioxidant activity, suggesting that the presence of secondary metabolites influenced the overall antioxidant activity of the plant. Substantially, the application of poultry manures positively influenced the growth, secondary metabolites and antioxidant activities of A. afra.