Co-composting of sweet sorghum biomass with different nitrogen sources

Composting of waste biomass from sweet sorghum seems to be a good alternative for its valorization in Portugal. The purpose of this work was to establish the best experimental conditions for the aerobic bioconversion of this material, starting with different C:N ratios and using different nitrogen sources. The material came from two fields with a fertilization level of 100 kg N/ha, and it was composted using bovine blood, domestic sludge and yeast extract as nitrogen sources, starting with initial C:N ratios of approximately 20 and 30. The experiment was carried out in a constant temperature chamber at 37°C and lasted for two and a half months. Samples were periodically collected and analyzed. The hygienic state of the product was also evaluated. The best quality compost from a fertilizer perspective was obtained with domestic sludge as a nitrogen source and starting from an initial C:N ratio equal to about 20:1. Starting from this C:N ratio could bring problems with the content of cadmium, so the recommended starting conditions must be about 30:1.