Why do legumes enrich soil?
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Answer: Root bacteria fix nitrogen
Leaves add organic matter — Wrong. All plant leaves decompose to add organic matter. Legumes specifically enrich soil through nitrogen fixation in root nodules with bacteria.
Flowers attract beneficial insects — Wrong. Pollinator attraction doesn't enrich soil. Legumes enrich soil through a symbiotic relationship with nitrogen-fixing bacteria in their roots.
Root bacteria fix nitrogen ✓ — Correct! Legumes (beans, peas, clover) have special root nodules containing Rhizobium bacteria. These bacteria convert atmospheric nitrogen gas into ammonia—a usable nitrogen form for plants. In exchange, the plant provides sugars. When legumes die or shed roots, this fixed nitrogen enriches soil. That's why farmers rotate crops with legumes!