Final answer:
The most productive soil in the U.S. is found in temperate zones with Type C climates, where the cycle of vegetation growth and die-off creates a rich layer of humus. Tropical rainforest soils are less nutrient-rich over time due to the lack of seasonal die-off.
Step-by-step explanation:
The climate with the most productive soil in the United States is not the tropical rainforest but rather the temperate zones with Type C climates. In these moderate and temperate climates, vegetation undergoes a cycle of growth and die-off, which contributes organic matter to the soil, forming a nutrient-rich layer known as humus. Humus acts as a natural fertilizer, replenishing the soil and making it highly fertile.
In contrast, tropical rainforest soils tend to be less nutrient-dense over the long-term because the vegetation does not die off seasonally, preventing the accumulation of humus. Therefore, temporary methods like extensive horticulture are employed to cultivate crops in nutrient-poor tropical soils, including slashing and burning to mimic the natural cycle of temperate regions.