H.P. “Sonny” Viator, Richard Bengston, Steven Hall, Lewis Gaston, Magdi Selim, Jim Wang, Benjamin Legendre, Thomas Hymel, Jimmy Flanagan, Jeff Hoy, Charles Kennedy and Jacqueline Prudente
Environmentally conscientious sugarcane growers voluntarily use best management practices (BMPs) to control runoff from production areas. Sugarcane is generally viewed as a conservation-friendly crop, with more than 20 BMP options for growers. Post-harvest residue management in sugarcane, however, is one area in need of research-based information to determine the best management approach.
Currently, surface residue generated during the harvesting operation is generally burned to minimize potential adverse effects of residue retention on subsequent sugarcane crops in the production cycle. Yield reductions of up to 25 percent can be caused by retaining the residue on the row tops until spring cultivation. The convenience and yield advantage of burning, however, may be offset by the possibility of higher rates of soil erosion and lower accumulation of organic matter on certain soils.
A series of experiments over five years from 2002 to 2007 at three locations – St. Gabriel, Jeanerette and Youngsville – were conducted to determine the influence of several of postharvest residue management practices on sugarcane production and water quality. All three sites included two management approaches – ground burning and full retention of the leafy material – which are currently employed by most growers. The St. Gabriel location also included sweeping the residue off the tops of the rows after harvest. The other locations included two treatments designed to mitigate the residue-retention problems by hastening decomposition of the residue. One treatment was the application of a combination of stabilized urea and composted “tea” (residue-degrading micro-organisms). The other treatment involved shredding the residue.
Edge-of-field runoff collections were sampled for contaminants using automatic water samplers, and runoff volume was measured by flow meters. Water quality parameters measured at St. Gabriel were total solids, total phosphorus, potassium and total nitrogen. Analyses for the Jeanerette and Youngsville sites included total suspended solids, total dissolved solids, turbidity, biological oxygen demand, total nitrogen, total phosphorus, nitrate, nitrite, chloride and sulfate. Total loads were calculated by multiplying concentrations by measured volume.
Loads at St. Gabriel reflected total annual runoff. The other two sites measured runoff only when flow depth and volume reached a prescribed amount. Consequently, load comparisons show relative differences between residue management treatments. Cane yield was measured by weight, and sugar content was determined by laboratory analysis of hand-harvested samples.
The influence on yield of the two common, industry-employed residue management treatments was consistent across the three locations and for all the years for which data were collected. Sugarcane harvested from the burned plots produced numerically higher but not statistically superior yields to the residue-retained plots. Soil loss and concentrations of nutrients in runoff were also similar among the residue-management regimes for all sites. There were, however, seasonal differences in soil erosion between the residue-burned and residue-retained practices, especially at the Jeanerette site.
From harvest until canopy closure in May or June each spring, erosion rates were higher for the burned plots than for the plots with retained residue. Before canopy closure, total suspended solids measured in the runoff water were approximately twice as high for the burned plots as for the plots in which soil was protected by residue. In both winter-spring periods in which runoff was sampled at Jeanerette, however, rainfall amounts were below normal, suggesting that the exposed soil in the burned areas would have been subject to higher erosion rates with higher rainfall.
The other treatments designed to mitigate the problems from residue retention were not effective. Shredding residue led to the highest amounts of soil erosion, and the urea/compost tea treatment generated unacceptable levels of nitrogen in the runoff water. Neither practice fostered yields higher than those of the other management practices. For these reasons, both the urea/compost tea and the residue-shredding treatments have been dismissed as viable practices.
The third practice evaluated at St. Gabriel – sweeping the residue to the furrow bottom – resulted in intermediate yields and water quality similar to those from the other two practices evaluated at St. Gabriel.
The failure of the evaluated practices to influence yield or water quality gives the sugar industry no new options for residue management. Soil losses measured in the series of studies were moderate and within the “acceptable” range of 2 to 5 tons of soil loss per acre per year. Without viable alternatives, growers will continue to burn until a management practice is identified to use the residue to reduce runoff while minimizing the impact of residue on the subsequent crops.
The BMP for prescribed burning encourages growers to use proven guidelines to manage smoke and large particulates. Louisiana sugarcane growers will continue to burn residue in the fields until research identifies ways to eliminate burning without reducing subsequent yields. Currently, LSU AgCenter researchers are looking for sugarcane varieties that tolerate the residue blanket and are evaluating practices that alleviate the yield-limiting effects of the retained residue.
H.P. “Sonny” Viator, Professor and Coordinator, Iberia Research Station, Jeanerette, La.; Richard Bengston, Professor, and Steven Hall, Associate Professor, Department of Biological & Agricultural Engineering, LSU AgCenter; Lewis Gaston, Associate Professor; Magdi Selim, Professor; and Jim Wang, Assistant Professor, School of Plant, Environmental & Soil Sciences, LSU AgCenter; Benjamin L. Legendre, Denver T. Loupe/American Society of Sugarcane Technologists Sugar Heritage Professor and Interim Head, Audubon Sugar Institute, St. Gabriel, La.; Thomas Hymel, Extension Agent, Iberia Research Station, Jeanerette, La.; Jimmy Flanagan, Extension Agent, Iberia Parish, LSU AgCenter, New Iberia, La.; Jeffrey W. Hoy, Professor, Department of Plant Pathology & Crop Physiology, LSU AgCenter; Charles Kennedy, Greenville Technical College, Greenville, S.C.; Jacqueline Prudente, Laboratory Services Division, Louisiana Department of Environmental Quality, Baton Rouge, La.
(This article was published in the spring 2008 issue of Louisiana Agriculture.)