| Summary: | Effects of irrigation were studied in Dioscorea hispida Dennst. (ubi gadong) in Terengganu, Peninsular Malaysia, by quantifying selected aerial agro-morphology and underground agronomical parameters in automated irrigation system. The control treatment for the frequency of water supplied was 1) watering at one day interval (T1); 2) watering at every day (T2); 3) watering at two days interval (T3); 4) watering at five days interval (T4); and 5) watering at six days interval (T5). In this research, the results indicated that T2 showed no significant difference with T1 and T3 for all parameters. The phytochemical analysis confirmed that irrigation frequency gave effects to secondary metabolites of D. hispida, where T2 showed the highest green colour index value and lowest yellow colour index value at -5.82 + 0.40 and 30.99 + 1.23, respectively, whilst its aqueous extract was more acidic than other treatments at pH 5.36 + 0.003, respectively. For laboratory bioassay test, aqueous extracts of tubers from T1 and T4 irrigation frequency treatments of D. hispida showed high significant differences from distilled water (control) to stimulate radical length elongations of maize and mustard, respectively. Furthermore, field trial has confirmed that allelopathy of D. hispida tuber aqueous extract of T1 had significantly triggered the highest plant height, total biomass weight and number of kernel of maize than control (distilled water). On the other hand, T4 showed significantly highest weight of total biomass and number of leaf of mustard than distilled water (control). The optimum allelopathic effects of D. hispida that were showed by T1 (control) and T4 (irrigated at five days interval in a week), might be due to the optimum concentration of allelochemicals produced in D. hispida tuber that has triggered the highest radicle elongation of maize and mustard, respectively.
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