Allelopathic Effect of Neem (Azadirachta indica) Leaf Extracts on Germination and Seedling Growth of Some Vegetable Crops

Aqueous leaves extract of different concentrations of Azadirachta indica or Neem was used to study the influence of their allelopathic effects on germination and growth of some vegetable crops namely cucumber, chilli and brinjal during January-July 2019 at the research laboratory of Agricultural Chemistry, Hajee Mohammad Danesh Science and Technology University, Dinajpur, Bangladesh. There were four treatments including control viz. T0=control, T1=3% aqueous extracts, T2=6% aqueous extracts, T3=9% aqueous extracts and T4=12% aqueous extracts of neem. Results showed that 12% aqueous leaf extracts greatlyinhibited the germination of the tested crops compared to other concentrations and showed the germination percentage was decreased with the increasing concentrations of leaf extracts. The highest seed germination percentage of cucumber, chilli and brinjal were 82.22%, 91.11% and 71.11% respectively in control treatment whereas the lowest germination was observed 55.55%, 66.67% and 40% at 12% aqueous leaf extract at cucumber, chilli and brinjal, respectively. Other germination parameters like germination speed, mean daily germination, peak value and germination value were also influenced by the leaf extracts. The highest root and shoot length were found at 3%, 6% and 9% leaf extract over control. Similar results were recorded for biomass allocation like root and shoot dry weight. The findings of the study showed that stimulatory and inhibitory effect of Azadirachta indica aqueous leaf extract may be due to the presence of secondary metabolites (allelochemicals) and the inhibitory effect was more pronounced at higher concentrations.