Sweet sorghum bagasse – A source of organic manure

Abstract

Bagasse or silage is an important byproduct in the sweet sorghumbased ethanol industry. Above ground biomass distribution in sweet sorghum forms 90% of the total biomass produced and that includes stem, leaves and panicle with grain. It is estimated that bagasse makes 30% of the total biomass of sweet sorghum, which is composed of cellulose (1525%), hemi cellulose (3550%) and lignin (2030%) with Net Calorific value: 4,125 Kcal kg1 (ash free); depending on the genotypes (Grassi 2001). Approximate composition of sweet sorghum bagasse is given in Table 1. It is estimated that 67 kg of bagasse will be produced for every liter of ethanol produced from sweet sorghum. Even though bagasse has multiple uses such as being a source for energy cogeneration, animal feed and organic manure, it is important to work out the tradeoffs between its uses as a source of biofuel and carbon balance in the whole productiontoconsumption chain. In this context, recycling of bagasse into organic manure and using it in the crop husbandry is an environmentally safe measure of sequestering carbon in the soil. Sweet sorghum is promoted in the semiarid regions where organic carbon content in the soil is generally low and the application of bagasse as organic manure assumes great importance for sustaining the soil fertility. The direct application of bagasse to the soil causes temporary lock up (immobilization) of soil nitrogen (N) due to wider C: N (~35:1) ratio and hence, it is important to bring down the C: N ratio by vermicomposting to use it as organic manure. Composting is the value addition method for enriching organic residues with low N content and this can be done either through microbial flora or along with earthworms. Generally, composting of organic residues with earthworms is referred to as vermicomposting, which is a rapid and simple method. The composition of vermicompost is superior in terms of macro and micro nutrients; besides, it is rich in plant growth promoting substances. The composting of sweet sorghum bagasse with earthworms is focused in the project and protocol was standardized for the same through laboratory and on farm trials.