Transfer of rubidium‐86 (potassium) from deeply‐rooted alfalfa (Medicago sativaL.) to associated, shallow‐rooted maize (Zea maysL.) or grain sorghum (Sorghum vulgarepers.).

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Abstract
Circumstantial evidence exists for non‐N‐mineral element transfer in legume‐grass associations. Three experiments were conducted in an effort to directly demonstrate transfer of a non‐N‐mineral element in alfalfa (Medicago sativa L.)‐maize (Zea mays L.) and alfalfa‐grain sorghum (Sorghum vulgare Pers.) associations in two rooting media. Associations were established in double‐tube apparatus so that a single alfalfa plant was rooted in media of top‐ and bottom‐tubes, while an associated grass plant was rooted exclusively in the top‐tube (Intact treatment). Severed treatments (the control) were identical to the Intact treatments except the alfalfa roots in an air gap between the top‐and bottom‐tubes were excised. 86Rb was dispensed onto the medium of bottom tubes with movement of the radioisotope determined by analyzing the legume and grass tissues over time. 86Rb was detected in: i) soil‐grown maize associated with alfalfa within a 40‐day treatment period; ii) sand‐grown maize associated with alfalfa within 20 days after treatment and iii) sand‐grown sorghum associated with alfalfa within 10 days. Detection of 86Rb in grass plants associated with alfalfa demonstrated that transfer of this potassium analog can occur via the root systems of legume‐grass associations.