الفهرس 
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Abstract
Legume plants play key roles in sustainable agriculture (Jia and Gray, 2008). Faba bean (Vicia faba L.), in particular, is one of the most important legumes in Egypt (Cazzato et al., 2012) and probably in many areas around the world (Crepon et al., 2010 and Boghdady et al., 2017). Its symbiotic relation with N-fixers can raise nitrogen content within different plant parts (Franche et al., 2009), especially protein in grains (Denton et al., 2013). These grains are consumed by both human and animals (Altuntaş and Yıldız, 2007) while crop residues can be used for fodder, silage purposes and to produce green manure (Sharaan et al., 2004; McVicar et al., 2013; and Nassar et al., 2016).
Organic matter (OM) is the life of soil (Reddy and Reddi, 1992) because it acts as a reservoir for macro- (N, P, K) and micro-nutrients (Farid et al., 2014 and 2018; Elshony et al., 2019). Also, organic amendments lessen nutrients losses by leaching from the top soil (Buckman and Brady, 1980; Pardo et al., 2014). Accordingly, it is recommended to amend soils with organic amendments to increase their fertility and supply plants with nutrient needed for their growth (Gomaa. and Attia, 1998 and Rizk and Shafeek, 2000) e.g. faba beans (Mohamed, 2001) and wheat (Farid et al., 2014). Moreover, organic amendments may effectively control soil-borne diseases and pests (Lazarovits et al., 2001; McSorley, 2011), stimulate the activities of beneficial microbes (Liu et al., 2009) and increase plant tolerance to diseases Biogas is one of the most economically viable and environmentally friendly renewable en