Nitrogen Fixation and Nitrate Assimilation of Determinate, Semi-determinate and Undeterminate Soybeans (Glycine max L.)

Soybean ( Glycine max L.) nitrogen nutrition is ensured by both symbiotic nitrogen fixation and mineral nitrogen assimilation. The relationship between these two modes of N nutrition was analysed in 3 growth types (determinate, semi-determinate and undeterminate) of soybean. The nitrate reductase activity and nitrogenase activity (acetylene reduction) of plants grown in the field and greenhouse showed that these enzymatic activity acted simultaneously or successively during the growth cycle, depending on the availability of inorganic nitrogen in the growing medium. Undeterminate soybean types had a higher potential nitrate reductase activities than determinate types.
The proportion of N₂ fixed as measured by ¹⁵N labelling or stem ureide content indicated that determinate soybeans derived a higher proportion of their N from N₂ fixation than the undeterminates.