Soru

For decades, soil scientists believed that Amazonian soils were universally infertile, depleted of organic nutrients by centuries of intense tropical weathering and leaching. However, the discovery of extensive deposits of Terra Preta de Índio ('Indian dark earth') across the Amazon Basin has challenged this long-held paradigm. Unlike the surrounding nutrient-poor oxisols, Terra Preta exhibits extraordinary fertility, characterized by high concentrations of persistent organic carbon, nitrogen, phosphorus, and calcium.

Recent archaeological and pedological analyses indicate that Terra Preta is not a naturally occurring soil type, but rather an anthropogenic product created by pre-Columbian Indigenous populations between 500 and 2,500 years ago. These ancient agriculturalists systematically enriched the soil through the controlled addition of biochar—a stable form of charcoal produced by low-temperature pyrolysis of organic waste—along with animal bones, fish remnants, and potsherds. The porous micro-structure of biochar acts as a molecular sponge, dramatically increasing the soil's cation exchange capacity (CEC). Consequently, Terra Preta retains essential plant nutrients and prevents them from being washed away by heavy rainfall, allowing nutrients to persist in the soil matrix for centuries without significant degradation.

Moreover, researchers have identified distinct microbial communities within Terra Preta that actively cycle nutrients and enhance soil resilience. While neighboring oxisols rapidly lose fertility after just a few crop cycles following clearing, Terra Preta fields maintain high agricultural yields indefinitely without requiring chemical fertilizers. Modern agronomists are currently examining the biochemical composition of Terra Preta to develop sustainable soil amendment strategies aimed at restoring degraded tropical soils worldwide.

According to the passage, the dramatic increase in Terra Preta's cation exchange capacity is explicitly attributed to which of the following factors?