Which factor is critical in determining the fertility of alluvial plains?

Soil composition and deposition from floodwaters are crucial factors in determining the fertility of alluvial plains. Alluvial plains are typically formed by the accumulation of sediments carried by rivers and streams, which deposit nutrient-rich materials during flooding events. This process enriches the soil with minerals and organic matter, creating an ideal environment for agriculture.

When floodwaters recede, they leave behind these nutrient deposits, enhancing the soil's fertility. The combination of fine particles with organic materials fosters a diverse and productive ecosystem, making alluvial plains among the most fertile lands for farming. The rich soil composition directly supports diverse vegetation and crops, contributing significantly to agricultural productivity.

While rainfall levels can influence agriculture, and temperature variations can affect growth cycles, the inherent soil composition and how it has been shaped by sediment deposition play a more direct role in establishing and maintaining fertility in these regions. Proximity to urban areas may have an impact on land use and access to markets but does not inherently determine the natural fertility of the land itself.