Allelopathy of Faba Bean Cover Crop to Durum Wheat Under a Semi-Arid Environment

Problems facing farmers practicing conservation agriculture in the semi-arid zone of Tunisia include appropriate cover crop selection, management of allelopathic effects affecting subsequent crop performance, and influence of seasonal variation on allelopathy expression. Allelopathy expressed by faba bean (Vicia faba L.) toward durum wheat [Triticum turgidum ssp. durum (Desf.) Husn.] was studied using bioassays during three growing seasons. The role of phenols in the expression of such potential was also investigated. Analyses of plant samples at three phenological stages (flowering, fruiting, senescence) revealed that leaves were most inhibitory. Allelopathic potential differed among plant components and phenological stages, with the greatest inhibitory effects occurring at senescence (49%). Inhibition varied across growing seasons, suggesting an environmental impact linked to inter-monthly water-balance variability. Inter-monthly rainfall appeared to be negatively related to the intensity of the allelopathic potential. The total phenolic content varied among plant components, phenological stages, and growing seasons, and the results implied that climatic variation may impact phenol accumulation in plant tissues. Total phenolics content of roots and stems significantly (p = 0.003 and 0.03, respectively) contributed to faba bean allelopathy. Use of faba bean as a cover crop preceding durum wheat carries a risk of allelopathic effects, which could negatively impact grain yield. Understanding the allelopathy of faba bean as a cover crop is critical for efficient management of residues under conservation agriculture.