Back To Top Recognize Effective Nodules Nodule size, shape and number vary with the host plant and Rhizobium strain. Red and white clovers have club-shaped and lobed nodules. Alfalfa nodules are more branched and longer, while cowpea, peanut and soybean nodules are spherical. Nodules on lateral roots may also be effective. If nodules have green or white centers, they are not actively fixing nitrogen and are ineffective.
Ineffective nodules are usually small and scattered over the entire root system.
Nodules form only on new roots and first appear evident when the first trifoliate or compound leaves appear, or within two to three weeks after seedling emergence. The exact lifespan of a given nodule is not known. This helps explain why ineffective and effective nodules may occur on legume roots at the same time. The pattern of nodule growth, decay and shedding is not the same in all legumes. Following cutting, nodules of most legumes are usually shed and new nodules form when root growth is renewed.