Final answer:
The major weakness of slash-and-burn farming is its unsustainable nature, which results in soil nutrient depletion and requires extensive land due to the impact of population growth.
Step-by-step explanation:
A serious weakness of slash-and-burn farming is the method's long-term unsustainability due to soil nutrient depletion and the need for extensive land use, which is exacerbated by population growth. In the slash-and-burn approach, a tract of forest is cut down, the vegetation dried, then burned. The resulting ash is used as a fertilizer, adding nutrients to the soil. However, these nutrients get rapidly depleted due to rain leaching. Consequently, the land becomes infertile within a few years, necessitating moving to a new area and starting the process again, which results in further deforestation.
Slash-and-burn can be sustainable in regions with low population densities, as it allows the forest to regenerate during fallow periods. With increasing populations, however, the fallow periods shorten, preventing forest regrowth and leading to a loss of biodiversity and worsening soil conditions. This pressure on the land accelerates habitat destruction and contributes to deforestation, making slash-and-burn an ecologically damaging practice over time.