Chapter 6 reveals the ways in which the Columbian Exchange affected global agriculture. It opens with the humble potato, a crop as important to human history as maize or sugarcane. The potato was first domesticated in the Andes. Native Andean peoples ate what was once a toxic tuber; they neutralized its toxins by dipping the cooked potato in a mixture of clay and water. Andean societies were highly developed with great highways and agricultural technologies such as raised fields and agricultural terraces which controlled erosion. The Spanish brought potatoes to Europe via the Columbian Exchange. Europeans were dubious at first about potatoes, unfamiliar with a cultivation process utilizing tubers. However, potatoes soon became an important part of European culture.

Growing seasons had become shorter because of the Little Ice Age. Potatoes were an answer to this agricultural difficulty because they could be planted and ready to harvest in a short period of time. Potatoes provided the answer to the Prussian famine of 1744 and improved Norway’s mortality rates. Most famously, potatoes provided sustenance for Ireland, preventing deaths from famine, and contributing to a population growth of 7 million people in two centuries.

As European farming became the norm—planting single crops in large, plowed fields—the need for fertilizer increased.