Since many tropical soils are already heavily weathered, they are highly vulnerable to nutrient loss and this is why many tropical soils are difficult arenas for the establishment of agriculture. Only about 20% of tropical soils are suitable for conventional agriculture, and many of these are found in alluvial plains and volcanic highlands. Disruptions of the nutrient cycle by clearing or burning (usually for agriculture or pasture) can be catastrophic for the soil, as nutrients will be rapidly lost and often the soil cannot support the same species as before, only an impoverished flora. A deforested experimental plot in Peru gave only moderate yields even with substantial inputs of fertilizer, but without them, yields dropped to zero. Even one crop depleted the soil too much for a good yield (Buol, 1995). Then, too, the organic materials contained in the nutrient-rich food crops are removed from the fields, not recycled as in a forest, and so are lost to the soil. Only the “refuse” or nonconsumable parts of the plants remain after harvesting to be decomposed and return to the soil as nutrients
deal is known about them.