Microbial degradation of post-harvest residues

Authors: Johnson, Richard; Richard Jr, Edward; Viator, Ryan; Grisham, Michael; BOOPATHY, RAMARAJ - NSU, THIBODAUX, LA

Submitted to: International Society of Sugar Cane Technologists Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2007
Publication Date: 7/20/2007
Citation: Johnson, R.M., Richard Jr, E.P., Viator, R.P., Grisham, M.P., Boopathy, R. 2007. Microbial degradation of post-harvest residues. Proceedings of the International Society of Sugar Cane Technologists. 26:365-373.

Interpretive Summary: In the past several years, Louisiana sugarcane producers have increasingly adopted green cane harvesting procedures. This is due primarily to the negative public and environmental impacts associated with burning standing cane, but also were necessitated in several years due to weather conditions unfavorable for burning. The Louisiana industry uses burning as a tool to remove the leafy material from the stalks to increase harvesting efficiency and sugar recovery and to reduce the impact of the plant residue generated at harvest on subsequent crops (ratoons). On-going research by the USDA-ARS-SRRC, Sugarcane Research Laboratory has documented that loses up to 15% of total harvested sugar-per-acre can occur if the leafy residues are not removed from fields prior to the start of a new growing season. In an attempt to find a solution to this problem, 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 9 bacterium and 7 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 these residues (19-25%) occurred when the isolates were combined into a consortium. Experiments also showed that the consortium degraded dry sugarcane leaves more (22%) than green leaves (14%) and sterilizing the residues prior to incubation did not effect 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. If this technology can be successfully developed, growers would inoculate their sugarcane fields a single time to establish the microbial consortium. The organisms would then be available to begin degrading the residues immediately after harvest in the fall well before the start of the subsequent ratoon crop’s growing season. Success in this line of research will allow sugarcane growers to utilize the blanket of post-harvest residues generated during the chopper harvesting of green cane to minimize the potential impact of soil, nutrient and pesticide losses from sugarcane fields without significantly impacting crop yields.

Technical Abstract: 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 9 bacterium and 7 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 these residues (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 sterilizing the residues prior to incubation did not effect 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.