Massive Accumulation of Calcium Carbonate and its Relation to Nitrogen Fixation of Sainfoin 1

Sainfoin ( Onobrychis viciifolia Scop.) has many desireable qualities as a legume forage, but it is not widely grown because of its lack of persistence and poor N‐fixation on many sites. The effect of competition by non‐N‐fixing soil microorganisms on N‐fixation was studied at 0, 50, 80, 95, and 100% levels of autoclaved soil sterization. Plants were grown aseptically for 30 days, dipped in Rhizobium inoculum, and transplanted to the sterilized soil. After 47 and 87 days in the growth chamber at 24/18 C, the plants were harvested. Nitrogen fixation was determined by the acetylene reduction capacity of the complete root system. Unexpectedly, root distortion accompanied by massive accumulation of CaCO 3 was stimulated in sainfoin roots that were grown in autoclaved soil to reduce the soil microorganisms. The purpose of the data presented is to describe the accumulation of Ca and its affect on N‐fixation in sainfoin. Distorted roots of plants grown in 100% sterilized soil contained up to 33% Ca. High levels of Ca in the roots were accompanied by low levels of Ca in the plant forage. Number of nodules produced and the capacity of roots for reducing acetylene decreased as root distortion and CaCO 3 accumulation increased. The properties of sterilized soil that stimulate CaCO 3 accumulation were not determined, but several possibilities are discussed. Root distortion also occurs in field‐grown plants and may be related to the decline of sainfoin stands in the field.