Slashing and burning is the preferred method of land clearing in the tropics for smallholders and large companies alike because it is cheaper, at least from a private perspective, and easier than available alternatives. In addition, fire eliminates field debris, reduces problems with weeds and other pests and diseases, makes nutrients available in the form of ash and loosens the soil to make planting easier. In some ways it is preferable environmentally compared to some other land-clearing methods.
For example, bulldozers and other heavy machinery cause soil compaction and erosion. Fire has many distinct advantages for low-income households: all other methods are more expensive; fire kills crop pests and diseases; and the ash provides much-needed fertilizer. Results of field experiments and surveys in Sumatra Indonesia demonstrate the key role that phosphorus (P) plays in resource management. Burning at low or medium intensity releases P into soil solution, but high-intensity fires reduce P levels. With greater fuel supply, hence hotter fires, the negative effects of heat on soil mineralogy offset the positive effects of additional ash.
