Composting of Sweet Sorghum Bagasse and its Impact on Plant Growth Promotion

The present study was carried out to optimize a protocol to rapidly decompose sweet sorghum bagasse and to evaluate the bagasse compost for plant growth promotion (PGP) in sweet sorghum. A total of ten cellulose-degrading microbes were screened for decomposing sweet sorghum bagasse, of which three (Myceliophthora thermophila ATCC 48104, Aspergillus awamori and Bacillus subtilis ATCC 6633) decomposed bagasse efficiently in 60 days. When these potential microbes were characterized for their in vitro PGP traits, all were found to produce indole acetic acid, cellulase, lipase (except M. thermophila) and siderophore (only A. awamori) and solubilize phosphorous (except M. thermophila). The bagasse compost prepared with the three microbes was evaluated for PGP on sweet sorghum under greenhouse conditions. The results showed that the bagasse compost prepared with potential microbes significantly and consistently enhanced PGP traits including the plant height (37–44%), leaf weight (63–81%), shoot weight (38–66%), root weight (87–89%), leaf area (75–83%) and root length (37–48%) at 35 days after sowing (DAS); shoot weight (40–58%) and root weight (24–38%) at 70 DAS; and shoot weight (30–46%), panicle weight (40–51%), seed number (20–62%) and seed weight (37–65%) at harvest over the bagasse compost prepared without microbes. Among the three potential strains, A. awamori and M. thermophila significantly and consistently enhanced all the PGP traits compared to B. subtilis. It is concluded that sweet sorghum bagasse can be decomposed rapidly and the bagasse compost prepared with microbes can be successfully used for PGP in sweet sorghum.