Why are tropical rainforest soils usually low in nutrients?

Tropical rainforest soils are typically deep but possess low fertility due to several key ecological factors:

• Leaching: Because rainfall in these regions is high and consistent, there is a nearly permanent surplus of water that moves downward through the soil. This process, known as leaching, washes essential mineral nutrients out of the soil profile and into streams and rivers.1
• Nutrient Cycling: A large proportion of the available nutrients in a rainforest ecosystem is bound up within the living biomass itself rather than being stored in the soil. Consequently, most plant roots are concentrated in the uppermost soil layers, where they can quickly absorb nutrients released from the decomposition of fallen leaves and organic litter.1
• Weathering: The hot, moist climate promotes intense weathering of rock. This leads to the development of deep, acidic soil profiles—often classified as Oxisols or Ultisols—that are rich in insoluble iron and aluminum oxides but depleted of essential nutrients like calcium, magnesium, and potassium.123