Antioxidant activity and soluble sugars of African ginger (Siphonochilus aethiopicus) in response to irrigation regimen and nitrogen levels

African ginger (Siphonochilus aethiopicus), as a medicinal plant, is known for its medicinal properties, containing various antioxidant compounds and carbohydrates. Rhizome yield is improved by water regimens and fertilizers applied at plant phenological stages. However, the rhizomatous herb, which is traditionally used for the treatment of asthma, inflammation and malaria has limited information on water and nitrogen requirements for its production. This study assessed the effect of irrigation regimens (30%, 50% and 70% allowable depletion level (ADL) and nitrogen (N) levels (0, 50, 100, 150 and 200kgha(-1)) on antioxidant activity and carbohydrates on plant leaf, root and rhizome. The interaction treatment effect of severely stressed (70% ADL) with the N application of 100kgha(-1) had significant effect on leaf phenolic concentration (87.02 +/- 2.51mgg(-1) gallic acid equivalent). Interaction effect of moderately stressed (50% ADL) and severely stressed (70% ADL) treatment with N application rate of 0kgha(-1) had significant effect on plant flavonoids and phenolics in all plant parts. In plant carbohydrates, root had high sucrose content (47.68 +/- 9.0mgg(-1) dry weight) with the application of low N (0kgha(-1)) grown under severely stressed treatment. In conclusion, this implies that different S. aethiopicus parts can produce substantial amount of antioxidants and carbohydrates, as exhibited under low N and reduced water supply applied during the phenological cycle.