Effectiveness of Post-Harvest Sugarcane Residue and Polyacrylamide on Reducing Soil Deposition in Quarter-Drains

Each spring, small ditches perpendicular to sugarcane rows (quarter-drains) that are responsible for transferring runoff from furrows to main ditches have to be re-conditioned to be effective. Bare soil surfaces in quarter-drains and furrows are exposed to intense rainfalls. Raindrop energy from rainfall causes detachment of soil particles and sediment transport from furrows through quarter-drains to main ditches. In time, sediment transported from furrows that accumulates in main ditches diminishes the capacity of these structures, thus requiring frequent and costly sediment cleanup. On average, yearly cost of sediment cleanup from surface ditches is $293/ha. Present practice in managing post-harvest residue is burning. However, burning is a questionable management practice and has a negative effect on the environment and human health due to discharging toxic gases into the atmosphere. An alternative to burning is to leave sugarcane residue on the surface after harvest. This practice could provide multiple benefits such as reducing soil sediment, enhancing soil quality in terms of increasing soil organic carbon, and decreasing cost for cleanup of surface ditches. To evaluate these benefits, an experiment was conducted to study effects of sugarcane post-harvest residue and Polyacrylamide (PAM) applied directly to quarter-drains in spring 2003. Twelve plots (0.1 ha each) were planted to sugarcane. For the residue treatment, residue was left on site after harvest and swept to furrows. Comparison was made with similar quarter-drains on six plots where residue was removed by burning. Treatments were: (1) residue left on the field; (2) no residue; (3) residue + PAM applied; and (4) no residue + PAM applied. Following each rainfall event, which produced runoff (four events), measurements of erosion/sedimentation depths were obtained. Based on the data, soil deposition in quarter-drains was the main process and the measurements represent the combined effect of treatments on the field and sediment transport through the quarter-drains. The sediment deposited in quarter-drains originated both from furrows and from side walls of quarter-drains. Sediment deposition rather than typically expected soil erosion in quarter-drains was related to unusually dry weather during the experiment. The sediment was measured at four locations along the length of the quarter-drain. A custom-made portable device was used to determine cross-sectional area of each semicircular quarter-drain at selected grid points. Based on four rainfall events with a cumulative depth of 105 mm, sugarcane residue left on the field significantly reduced soil deposition by 28% in quarter-drains compared to residue removed by burning. Results also show that, in addition to residue left on the field, applying an aqueous PAM solution to quarter-drains further reduced soil deposition by 34%; however, no significant difference in soil deposition was found between residue only and residue + PAM treatments. Data suggest that PAM effectiveness was likely inhibited by abnormally dry and hot weather in spring, 2003, and might be related to the polymer's chemical, photo, and mechanical degradation. Leaving sugarcane residue on the field after harvest instead of burning could reduce soil loss from furrows and surface drains by 4.2 tons per year. This type of residue management might also provide economical benefits due to reducing reformation cost of surface drainage ditches within the field with an average yearly savings of $106/ha.