Over the past decade, sugar cane farmers worldwide have considered the options of switching from burnt cane harvesting to green cane harvesting. Researchers have found soil and climate play a part in the efficiency of green cane harvesting vs. burnt cane harvesting. In Florida, switching to green harvesting could both increase the cost of harvesting and reduce the yield.

In Florida, “green” harvesting instead of burning sugar cane fields before the harvest would not be effective during the colder months of the year, according to “The Effect of Harvest Method and Microclimate and Sugarcane Yield in Florida and Costa Rica,” published in 2010 by R.A. Gilbert, G. Kingston, K. Morgan, R.W. Rice, L. Baucum, J.M. Shine and J.F. Subrios.

The study explains, “There is a worldwide pressure on sugarcane industries to adopt ‘green cane’ harvesting systems that do not involve burning. The objective of this study was to compare the effect of sugarcane harvest methods on cane productivity and microclimate in Florida, U.S.A. and Costa Rica.”

Experiments were conducted at three sites: Everglades Research and Education Center (EREC), Belle Glade, Florida, on a muck Histosol with high organic matter; Hilliard Brothers Farms, Florida, on an Entisol with sandy texture; and, Azucarera El Viejo mill in Guanacaste, Costa Rica, on a clay loam Inceptisol.

The researchers found there was a trend for higher biomass yields in burnt cane when harvested early (November through January). Cane yields were not different when harvested late in the season (mid-February through March). However, the study found a significant cumulative three-year difference favoring burnt vs. green cane treatments.

The researches found the fields harvested by the green cane method suffered from lower ground temperatures during frosts. The sun warms the soil during the day in the burnt cane fields, but the cane trash left by green harvesting prevents the sun from warming the soil in those fields. The difference in temperature was shown to be damaging to the young cane shoots, which led to significantly less yield in the first ratoon. (After it is planted, cane can be harvested two to four times, depending on the type of cane. Each growth period is called a ratoon.)

“Our results indicate that green cane residues have a significant effect on microclimate and that green cane harvest in Florida would be better suited for late rather than early harvest time periods,” the authors concluded.

“There are major agricultural concerns with the green cane system because, under specific conditions, it has been shown to reduce sugarcane biomass and sugar yields due to excessive soil wetness, lower soil temperatures, slower ratoon crop regrowth rates, and possible allelopathic effects. Heavy crop residues left on the fields may facilitate higher pathogen and pest pressures,” the researchers found.

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival and reproduction of other organisms.

Additionally, cane trash residue generally impedes effective cultivation, they found: “Twenty-five to 30 percent of the above-ground biomass in sugarcane is present as leaves and tops (commonly referred to by sugarcane growers as the cane trash) and is undesirable from the standpoint of processing for sugar and molasses. Pre-harvest burning destroys the trash, and increases the efficiency and profitability of the harvesting process.”

Sugarcaneresearch.com compared the advantages and disadvantages of green and burnt cane harvesting.

• Burnt cane harvesting results in lower “cane trash” and extraneous matter — 3% to 7%, compared with 4% to 15% for green harvesting.
• Burnt cane harvesting is significantly cheaper than green cane harvesting.
• Burnt cane is easier to harvest.
• With burnt cane harvesting, the harvest must be completed within 24 hours to avoid deterioration.
• Green cane harvesting has better productivity in showery conditions when burning may not be possible.
• In drier areas, green cane harvesting requires less irrigation.
• Green cane losses during harvesting are higher with losses ranging from 5% to 25% depending on extractor fan speed.

• Green cane harvesting is more expensive, as cutting rates are only 60% to 70% of those in burnt cane and fuel costs are higher.
• Green cane trash blanketing may not be suitable for some situations such as: poorly drained blocks which may be slower in ratooning; cool, wet conditions may be slower in ratooning; Burdekin, where furrow irrigation on heavier soils is more difficult.

A 2007 study by Oscar Nunez and Egbert Spaans was detailed in “Evaluation of Green Cane Harvesting and Crop Management with a Trash Blanket.” This study evaluated the green cane harvest at San Carlos Sugar Mill in Ecuador.

“Two sites were harvested green by hand and compared with two adjacent sites that were also harvested manually but burned. Manual, green cane harvesting was found to be not feasible for San Carlos Mill due to the prohibitive increase in harvesting cost caused by the reduction in productivity of 68% of the field laborers,” the authors explain. “Subsequently, an experiment was undertaken with mechanical harvesters, comparing six sites that were cut green and another six adjacent sites that were burned before harvest. In mechanical green-cane harvest, the machine productivity was reduced by 43% and the trash content in the delivered cane was higher by 38%.”

The researchers found some advantages to green cane harvesting in this area. The cane trash left by the green harvest helped return more nitrogen to the soil.

“After considering the impact of all the parameters that were monitored, economic analysis currently favors burned-cane harvest,” they wrote. They also opined green harvesting deserves more study.

“It is necessary to continue the evaluation of mechanical green-cane harvest to understand the conditions under which it is favorable and to assess its long-term effects on soil health and cane yield,” they wrote.