Researched
Legumes Fix Nitrogen
Hellriegel and Wilfarth showed in 1886-88 that legumes live on air nitrogen through root-nodule bacteria; Beijerinck grew them in pure culture in 1888.
Open in the interactive tree →Farmers had long seen fields recover after peas, beans or clover, but chemists could not say where the nitrogen came from. Hermann Hellriegel and Hermann Wilfarth grew peas in heated, nitrogen-poor soil: the plants formed root nodules and thrived only when given a soil extract, and otherwise starved. In 1888 Martinus Beijerinck isolated the nodule bacteria, now called rhizobia, in pure culture. Rhizobia are still added to seed on 12 to 20 million hectares of soybeans each year.
Prerequisites
- Crop Rotation (Norfolk System)~1730Farmers had long seen clover and peas restore tired fields.
- Mineral Fertilizer1840The dispute over where plants get nitrogen drove the experiments.
- Germ Theory1861Pure-culture methods showed that root bacteria do the work.
Unlocks
- Nitrogen-Fixing CerealsopenSelf-fertilising cereals would copy the legume-rhizobia partnership found here.