Dynamics of the functional groups in the weed flora of dryland and irrigated agroecosystems in the Gangetic plains of India
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The relative abundance of the weed functional types in dryland and irrigated rice in the Kharif (summer) crop field and dryland lentil and wheat in the irrigated Rabi (winter) crop field was studied at the agricultural farm of Banaras Hindu University,Varanasi, India. A total of 22 species, belonging to 17 families,was recorded in the dryland and irrigated rice ecosystems and 18 species, belonging to eight families,were recorded in the dryland lentil and irrigated wheat ecosystems.The ImportanceValue Index (IVI) of the hemicryptophytes showed an increasing trend with the crop growth period in the case of the dryland rice, whereas in the irrigated rice plots, a reduction in the IVI of the hemicryptophytes, with a related increase in the importance of the therophytes,was observed as the crop attained maturity.Also, the trend of a decreased IVI was observed for the geophytes in the fertilized dryland rice plots.The principal components analysis (PCA) ordination showed the uniqueness of the crop plot in terms of weed species composition.The PCA analysis of the functional types on the basis of the crop plots indicated that the hemicryptophyte and therophyte weed species composition was heavily altered at the initial and final sampling, although the weed flora was dominated by the therophytes and geophytes. These results suggest the prioritization of hierarchical temporal management options for the functional weed types in different crop plots and that this approach warrants further investigation.