Allelopathy in jatropha plantation: Effects on seed germination, growth and yield of wheat in north-west India

In-situ and ex-situ allelopathic effects of jatropha (Jatropha curcas L.) were analyzed by studying growth and yield of wheat (Triticum aestivum L.). Ex-situ approach included studying laboratory bioassay of leaf aqueous extract effects on seed germination and seedling growth; and pot experimentation with different jatropha plant parts as soil amendments. Wheat was grown under the jatropha plantation in in-situ approach. To eliminate the shade effects of jatropha, a treatment plot was prepared by cutting jatropha trees to 0.5 m above ground level. Bioassay indicated the inhibitory effects of leaf extracts, particularly at high concentrations on seed germination and seedling growth of wheat. In ex-situ pot experiment, soil amendments with different plant parts enhanced biomasses and grain yields of wheat. Increase in yield and biomass was higher in pots amended with jatropha fruit, followed by leaf and stem. When wheat crop was grown with jatropha in in-situ approach, results were more conclusive as the ill effects of jatropha were not seen in pruned plants plots. Grain yield and biomass declined under the standing jatropha cultivation, with lowest reduction in low plant population density plots. Thus, an inhibitory effect of jatropha on wheat was limited to ex-situ bioassay only. Winter shedding of leaves in jatropha could be a boon for the Rabi (winter season) intercrops, and wheat could be an option for its cultivation under low plant population densities of jatropha with limited irrigation in north-west India.