Microbial Degradation of Post-harvest Residues

MANAGEMENT of post-harvest residues, produced during the green-cane harvesting of sugarcane in Louisiana, has become an increasingly important issue for producers, particularly in areas where burning of the residues is banned or restricted. If the residues, which range from 4–8 tonnes per hectare, are not removed prior to the emergence of the subsequent ratoon crop in the spring, yields may be reduced from 4.5 to 13.5 tonnes per hectare. A study was initiated to determine if native bacteria and fungi that were capable of degrading post-harvest residues could be identified and used to accelerate residue decomposition. Soil was collected from five locations, and nine bacteria and seven fungi capable of degrading cellulose were isolated. These isolates were evaluated using wet fermentation techniques, and two bacterial and two fungal isolates capable of degrading from 32–52% of available cellulose were selected for further study. In dry fermentation and in non-sterile greenhouse studies, the most efficient degradation of residue (19–25%) occurred when the isolates were combined into a consortium. Experiments also showed that the consortium degraded dry sugarcane leaves significantly greater (22%) than green leaves (14%), and sterilising the residues prior to incubation did not affect decomposition. When the carbon to nitrogen ratio of the residue was varied from 10:1 to 50:1, the total residue degraded decreased from 28 to 19%. Finally, results from a field study showed that populations of these isolates steadily increased after soil inoculation indicating their successful establishment in the field. Although total residue levels were not significantly affected, soil organic carbon significantly increased where the consortium was applied compared to the control, suggesting that decomposition is being accelerated by the addition of the microbes.