How were legumes used in crop rotation before synthetic fertilizers became common?

Before the widespread use of synthetic fertilizers, legumes were essential to agriculture due to their unique ability to perform nitrogen fixation. Through a symbiotic relationship with Rhizobium bacteria in their root nodules, legumes convert atmospheric nitrogen into compounds that enrich the soil, supporting plant growth.12

In traditional farming, this process was utilized through crop rotation, which typically involved alternating a cash grain crop, such as corn, with a legume, such as alfalfa. This practice provided several agricultural benefits:1

• Soil Enrichment: As legume roots decayed, they released nitrogen compounds into the soil, providing natural fertilization for subsequent crops.1
• Forage Production: Legumes like alfalfa or clover served a dual purpose by providing valuable animal feed in the form of hay or silage.1
• Soil Protection: Legumes were often used as cover crops to reduce soil erosion and could be plowed under as green manure to further improve soil quality.1
• Weed Management: Rotating crops helped disrupt the growing environment, which assisted in controlling weeds.1