Anaerobic Digestion Reduces Seed Germination and Viability of Six Plant Species from the Upper Nile Valley, Egypt

Anaerobic digestion (AD) involves the breakdown of a substrate by mixed microbial communities in the absence of free oxygen. This process has many benefits leading to the production of bioenergy (biogas) and fertilizers (bio-fertilizers). Unfortunately, the bio-fertilizer made using AD may be contaminated with weed seeds and may have the potential of infesting the fields to which it is applied. Thus, the goal of this study is to determine the effects of AD on seed germination and viability of two undesirable crop plants (Triticum aestivum and Sorghum bicolor) and four weed species of reclaimed agricultural land near Qena, Egypt (Schouwia purpurea, Polygonum equisetiforme, Amaranthus viridis, and Lotus arabicus). Vegetative biomass of T. aestivum was used as the substrate, and cattle rumen fluid was used as the inoculum. The seeds of the six plants were placed in culture bottles and subjected to AD at 37 ± 2 °C for up to 16 days. Time to first germination (the time required for the first seed to germinate) and the percentage of seeds that germinated varied among the six species. The percentage germination of all six species decreased with increasing duration of AD, with no seeds germinating at 12 or 16 days of incubation. Seeds of T. aestivum and S. bicolor experienced a rapid and significant decrease in the percentage of viable seeds and an increase in the percentage of non-viable seeds. In contrast, even though they did not germinate, some seeds of the other four weed species remained viable, even after 16 days of incubation. Approximately 32% of S. purpurea seeds remained viable at 16 days of incubation. Overall, our results suggested that the application of anaerobic digestate in the reclaimed agricultural lands near Qena, Egypt, is not likely to exacerbate weed infestations in these fields.