Slash and burn agriculture is a widely used method of growing food in which wild or forested land is clear cut and any remaining vegetation burned.
The resulting layer of ash provides the newly-cleared land with a nutrient-rich layer to help fertilize crops. (EcoLogic)
In the Islands, between AD 1100 and 1650, there was a period of expansion and agricultural intensification in Hawaii that accompanied an increase in human population. (Pratt)
Until about 1500 AD, agriculture was shifting cultivation using slash and burn techniques and long fallow periods. Between 1500 and 1800 A.D., agriculture expanded, intensified, and became permanent. (Cuddihy & Stone)
During that period the lowland vegetation below 1,500-feet elevation was almost entirely replaced by cultivated fields, dispersed settlements and grasslands, caused by repeated fires; while upland sites remained little disturbed. (Pratt)
Several of the large field systems have pronounced burn layers that represent wither the original removal of native tree cover or the use of fire for clearing fallow fields.
Fire was the primary tool used by Hawaiians to clear lands prior to cultivation. This was true in areas adjacent to irrigated valleys and windward slopes as well as in the great field systems. Fire may have been repeatedly used to periodically clear the secondary growth on fallow fields. (Cuddihy & Stone)
Fire was also used in marginal cultivations to burn off vegetation and increase the cover of ‘ama‘u ferns used as pig feed. Large expanses of the lowlands were regularly burned to clear woody vegetation and stimulate indigenous pili grass. (Pratt)
Agricultural burning is standard practice for many other kinds of crops on nearly 9-million acres throughout the country, including rice, wheat, corn, cotton, lentils and soybeans. (HC&S)
Fire was later used in the harvesting of sugarcane. Burning the cane before harvesting removes most of the dead vegetation without causing significant damage to the interior of the cane stalk. (James)
The sugarcane plant consists of about 75 percent to 80 percent net cane (stalks) from which the juice is extracted and the sugar crystalized. The other 20 percent to 25 percent of the plant consists of leafy material, including tops, from which little or no sugar is produced.
This leafy material is called trash. Burning sugarcane before harvest (or milling) removes from one-half to two-thirds of this trash that would otherwise contribute nothing to sugar production. (LSUAC)
In many countries, such as Brazil, Guatemala, Mexico, and Costa Rica, pre-harvest burning is a common practice. In the US and Philippines, sugarcane fields are burned either before or after harvest, but in India, most of the sugarcane residues are usually burned in the field only after harvest. (de Azeredo França)
In Australia, sugarcane burning started in the 1930s to combat Weil’s disease (leptospirosis) among cane-cutters. In other cane growing areas, burning was sometimes done to clear the field of snakes before hand-cutters cut the cane. (Cheesman)
There were attempts to use fire to get rid of pests, “When as an experiment, a patch of about nine acres of cane, so heavily attacked by leaf-hopper as to be useless, was set on fire all around to destroy these, it was noticed that the adult hoppers rose from the cane in a cloud and spread to other fields; so this plan for destroying them was of no value.” (HSPA, 1906)
It appears that the practice of burning sugarcane started in the early-1900s (some suggest in 1908.) Prior to that, cane trash (nonproductive leafy parts of the cane) was removed by hand (men chopped the cane; ‘holehole’ work, stripping the dried cane leaves, was deemed ‘women’s work.’)
The sugar in burned cane inverts after 48-hours and the lack of ability to quickly transport burned cane to mills limited its practice until the late-1920s when a macadamized road system and diesel trucks across the islands became widespread. (Hayakawa)
Later, pre-harvest burning, in the field, was the only economical means sugar planters found for removing the dried leafy material from its crop.
Removal of this dried leafy material reduces the quantity of material which needs to be hauled to the factory, including the soil adhering to the harvested material; reduces the number of haulers traveling back and forth and therefore reduces fuel consumption; reduces the amount of material the factory must handle and therefore its energy consumption; and improves sugar recovery. (HC&S)