The Ancient Science of Rotation
Crop rotation is one of humanity's oldest agricultural innovations. The Roman writer Virgil described two-field rotation in 30 BCE, and medieval European farmers developed three-field systems that sustained populations for centuries. The Norfolk four-course rotation — wheat, turnips, barley, clover — triggered an agricultural revolution in 18th-century England by eliminating fallow years entirely.
Nitrogen: The Limiting Factor
Nitrogen is the nutrient most often limiting crop growth. While the atmosphere is 78% nitrogen gas, plants cannot use it directly. Legumes solve this through symbiosis with Rhizobium bacteria that convert atmospheric N₂ into plant-available ammonium. A single hectare of clover can fix 150 kg of nitrogen — equivalent to several bags of synthetic fertilizer — while simultaneously improving soil structure.
Beyond Nutrients: Breaking Pest Cycles
Rotation does more than manage nutrients. Many crop pests and diseases are host-specific: corn rootworm larvae starve if they hatch in a soybean field. Rotating crops breaks these biological cycles, reducing the need for pesticides. This is why monoculture — planting the same crop year after year — typically requires escalating chemical inputs to maintain yields.
Modeling Long-Term Soil Health
This simulation tracks soil nitrogen through yearly cycles of crop uptake, legume fixation, organic matter mineralization, and leaching losses. Adjust the rotation length, legume fraction, and fallow periods to find strategies that maximize both yield and long-term soil fertility. The sustainability score rewards rotations that maintain stable nitrogen levels without declining yields.