Sugarcane is a perennial grass cultivated globally in tropical and subtropical regions, primarily for its sucrose-rich stalks used in sugar production and biofuels. Harvesting often involves a controversial practice called pre-harvest burning, or “trashing” the cane. This process involves intentionally setting the fields alight just before harvesting to remove the leafy material surrounding the stalk. This tradition was adopted historically to maximize efficiency and lower costs for the grower.
Logistical and Economic Reasons for Pre-Harvest Burning
Farmers burn sugarcane primarily to remove the dense, dry leaf material, known as “trash,” which makes up between 20% and 30% of the total cane mass. This leafy residue impedes the harvesting process, whether the cane is cut manually or mechanically. Burning this biomass ensures that only the heavy, sugar-bearing stalks remain for collection.
Removing the trash greatly increases the speed and safety of the harvest operation. For manual laborers, the fire drives out or kills snakes, rodents, and stinging insects living within the dense cane stalks, making the fields safer to enter. The lack of sharp leaves allows workers to cut the cane more quickly, significantly raising the daily output per person. This efficiency translates directly into lower labor costs and a shorter overall harvest season.
Burning also offers economic benefits related to transportation and milling. The process eliminates tons of non-sugar-producing material, reducing the weight hauled from the fields to the sugar mill. This reduction saves on fuel consumption and wear-and-tear on vehicles and public roads. At the factory, less trash means less material to process, which improves milling efficiency and reduces water consumption before juice extraction.
Environmental and Public Health Impacts
Despite the logistical advantages for the grower, pre-harvest burning creates significant negative externalities for the environment and public health. The fires release a massive plume of smoke containing fine particulate matter (PM), including PM2.5 and PM10. These particles are small enough to be inhaled deep into the lungs and are linked to increased rates of respiratory distress, asthma, and cardiovascular hospitalizations in nearby communities.
The smoke also contains volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and greenhouse gases, contributing to regional air pollution. Sugarcane fires emit carbon dioxide, methane, and nitrous oxide, all of which contribute to climate change. In some regions, the PM2.5 released is comparable to emissions from motor vehicles, contributing to premature mortality rates.
The high heat of the fires severely impacts agricultural soil health. Burning destroys beneficial soil microorganisms and removes the layer of organic matter that would naturally decompose and enrich the ground. This loss of organic material increases the need for chemical fertilizers in subsequent seasons. Without the protective layer of cane trash, the soil is vulnerable to wind and water erosion, leading to sediment and nutrient runoff into nearby water bodies.
Transitioning to Green Harvesting Methods
Growing awareness of these negative health and environmental outcomes has driven a global shift toward green harvesting methods. Green harvesting involves cutting the cane stalks without burning the field first, a process made possible primarily by specialized mechanical harvesters. These machines use powerful fans to separate the green leaves and tops from the stalk, leaving the leafy residue, or “trash,” directly in the field.
This residual cane trash is left on the ground to form a trash blanket or mulch layer. This layer delivers multiple agronomic benefits, starting with improved soil health. The mulch acts as a natural weed suppressant, reducing the need for herbicides and cutting weed control costs. The blanket also conserves soil moisture, reduces evaporation, and helps protect the soil from erosion.
The trash blanket slowly decomposes, returning organic carbon, nitrogen, and other essential nutrients to the soil. This natural nutrient cycling reduces the amount of synthetic fertilizer farmers need to apply over time. Many sugarcane-producing regions, including Australia and Brazil, have largely adopted this practice, and regulatory pressure is increasing in other areas to phase out pre-harvest burning due to its adverse effects on public health and air quality.